sci.electronics.repair@googlegroups.com

Today's topics:

* another puzzler - 5 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/b80657d8be4c22cd?hl=en
* What kills a valve rectifier? - 11 messages, 5 authors
http://groups.google.com/group/sci.electronics.repair/t/3452d3f8314c6ded?hl=en
* GOOD STUDY METERIAL - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/f752940733af7245?hl=en
* PC Power Supply Recommendations? - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/5d9c672c7593977e?hl=en
* Wall Warts - 6 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/de407a5056a54ee0?hl=en
* Discount Wholesale Affliction Jeans Armani Jeans Christian Audigier Jeans
True Religion Jeans and so on <free shipping > (http://www dot 24hours-online
dot com/ ) - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/0a15200ee5975ba8?hl=en

==============================================================================
TOPIC: another puzzler
http://groups.google.com/group/sci.electronics.repair/t/b80657d8be4c22cd?hl=en
==============================================================================

== 1 of 5 ==
Date: Tues, May 24 2011 12:06 am
From: "Trevor"

"Trevor" <trevor@home.net> wrote in message
news:4ddb578e$0$22471$afc38c87@news.optusnet.com.au...
> "Don Pearce" <spam@spam.com> wrote in message
> news:4dd79a03.316359700@news.eternal-september.org...
>>>>>> Suppose for the moment that there are two contestants. One picks door
>>>>>> two, and the other picks door one. Then the moderator opens door
>>>>>> three
>>>>>> and shows everyone that there is a donkey behind that door. Now, will
>>>>>> it
>>>>>> make any difference if the other two switch their initial picks or
>>>>>> not?
>>>>>> And, if they do swap doors, with they both enjoy a 2/3 chance of
>>>>>> winning?
>>>>>
>>>>> In this scenario, once the third door is opened, they each have a
>>>>> 50/50 chance of winning, and there is no advantage in swapping
>>>>> choices. Before the revelation their chances of winning were 1/3. If
>>>>> it seems illogical that the odds are changed by this revelation,
>>>>> remember that one time in three the host will reveal, not a goat, but
>>>>> the car.
>>>>>
>>>> Only if the host opens a door at random, which isn't the case in the
>>>> classic Monty Hall problem. The host knows where the car is, and always
>>>> opens one of the other doors.
>>>
>>>Er, the host can't open one of the other doors now, since they have both
>>>already been selected by the two contestants. If he does however, and
>>>reveals a goat, then that contestant now has a ZERO chance of winning
>>>obviously, with the remaining contestant on 66%.
>>>Try actually re-reading the new scenario presented.
>>>
>>>
>> I think maybe you need to re-read. Each contestant picks a door, then
>> the host opens the remaining door. If he exposes a goat, then at least
>> one of the contestants gets a car. In fact either of the contestants
>> will get the car, with a 50/50 chance.
>
>
> NOPE, IF the host picks the remaining door he now has a 1/3 chance of the
> big prize, and the other two also have only a 1/3 chance each of the big
> prize, NOT 50:50.

I should have added that yes IF (and only IF) the host reveals a goat, the
other two will now have a 50:50 chance, but surely that is obvious, and
remains so whether they both switch or both stay, so is NO Longer like the
original MH problem at all.

Trevor.

== 2 of 5 ==
Date: Tues, May 24 2011 8:26 am
From: spam@spam.com (Don Pearce)

On Tue, 24 May 2011 17:00:57 +1000, "Trevor" <trevor@home.net> wrote:

>
>"Don Pearce" <spam@spam.com> wrote in message
>news:4dd79a03.316359700@news.eternal-september.org...
>>>>>> Suppose for the moment that there are two contestants. One picks door
>>>>>> two, and the other picks door one. Then the moderator opens door three
>>>>>> and shows everyone that there is a donkey behind that door. Now, will
>>>>>> it
>>>>>> make any difference if the other two switch their initial picks or
>>>>>> not?
>>>>>> And, if they do swap doors, with they both enjoy a 2/3 chance of
>>>>>> winning?
>>>>>
>>>>> In this scenario, once the third door is opened, they each have a
>>>>> 50/50 chance of winning, and there is no advantage in swapping
>>>>> choices. Before the revelation their chances of winning were 1/3. If
>>>>> it seems illogical that the odds are changed by this revelation,
>>>>> remember that one time in three the host will reveal, not a goat, but
>>>>> the car.
>>>>>
>>>> Only if the host opens a door at random, which isn't the case in the
>>>> classic Monty Hall problem. The host knows where the car is, and always
>>>> opens one of the other doors.
>>>
>>>Er, the host can't open one of the other doors now, since they have both
>>>already been selected by the two contestants. If he does however, and
>>>reveals a goat, then that contestant now has a ZERO chance of winning
>>>obviously, with the remaining contestant on 66%.
>>>Try actually re-reading the new scenario presented.
>>>
>>>
>> I think maybe you need to re-read. Each contestant picks a door, then
>> the host opens the remaining door. If he exposes a goat, then at least
>> one of the contestants gets a car. In fact either of the contestants
>> will get the car, with a 50/50 chance.
>
>
>NOPE, IF the host picks the remaining door he now has a 1/3 chance of the
>big prize, and the other two also have only a 1/3 chance each of the big
>prize, NOT 50:50.
>
>trevor.
>
>
>
>
The host doesn't pick the remaining door, he opens it. He reveals a
goat/donkey whatever. That means the two contestants have door each,
one of which has a car behind it. They now each have 50/50 odds. There
is nothing in this scenario that puts one contestant's odds higher
than the other since they both picked a door each at the start.

d

== 3 of 5 ==
Date: Tues, May 24 2011 8:27 am
From: spam@spam.com (Don Pearce)

On Tue, 24 May 2011 17:06:22 +1000, "Trevor" <trevor@home.net> wrote:

>
>"Trevor" <trevor@home.net> wrote in message
>news:4ddb578e$0$22471$afc38c87@news.optusnet.com.au...
>> "Don Pearce" <spam@spam.com> wrote in message
>> news:4dd79a03.316359700@news.eternal-september.org...
>>>>>>> Suppose for the moment that there are two contestants. One picks door
>>>>>>> two, and the other picks door one. Then the moderator opens door
>>>>>>> three
>>>>>>> and shows everyone that there is a donkey behind that door. Now, will
>>>>>>> it
>>>>>>> make any difference if the other two switch their initial picks or
>>>>>>> not?
>>>>>>> And, if they do swap doors, with they both enjoy a 2/3 chance of
>>>>>>> winning?
>>>>>>
>>>>>> In this scenario, once the third door is opened, they each have a
>>>>>> 50/50 chance of winning, and there is no advantage in swapping
>>>>>> choices. Before the revelation their chances of winning were 1/3. If
>>>>>> it seems illogical that the odds are changed by this revelation,
>>>>>> remember that one time in three the host will reveal, not a goat, but
>>>>>> the car.
>>>>>>
>>>>> Only if the host opens a door at random, which isn't the case in the
>>>>> classic Monty Hall problem. The host knows where the car is, and always
>>>>> opens one of the other doors.
>>>>
>>>>Er, the host can't open one of the other doors now, since they have both
>>>>already been selected by the two contestants. If he does however, and
>>>>reveals a goat, then that contestant now has a ZERO chance of winning
>>>>obviously, with the remaining contestant on 66%.
>>>>Try actually re-reading the new scenario presented.
>>>>
>>>>
>>> I think maybe you need to re-read. Each contestant picks a door, then
>>> the host opens the remaining door. If he exposes a goat, then at least
>>> one of the contestants gets a car. In fact either of the contestants
>>> will get the car, with a 50/50 chance.
>>
>>
>> NOPE, IF the host picks the remaining door he now has a 1/3 chance of the
>> big prize, and the other two also have only a 1/3 chance each of the big
>> prize, NOT 50:50.
>
>I should have added that yes IF (and only IF) the host reveals a goat, the
>other two will now have a 50:50 chance, but surely that is obvious, and
>remains so whether they both switch or both stay, so is NO Longer like the
>original MH problem at all.
>
>Trevor.
>
>
Of course - and that is precisely the new scenario presented. As I
said - re-read. And no, it is nothing like the original MH problem.

d

== 4 of 5 ==
Date: Tues, May 24 2011 6:57 pm
From: "Trevor"

"Don Pearce" <spam@spam.com> wrote in message
news:4ddbcd36.591611280@news.eternal-september.org...
> The host doesn't pick the remaining door, he opens it. He reveals a
> goat/donkey whatever. That means the two contestants have door each,
> one of which has a car behind it.

ONLY if it is not behind the one the host already opened. Since he no longer
has a choice of doors, he must have a 1/3 chance of showing the car.

>They now each have 50/50 odds. There
> is nothing in this scenario that puts one contestant's odds higher
> than the other since they both picked a door each at the start.

Right, where did I say otherwise, IF the host has not already shown the car?
The whole point is that the game is now no longer like the Monty Hall
scenario in any way.

Trevor.

== 5 of 5 ==
Date: Tues, May 24 2011 7:00 pm
From: "Trevor"

"Don Pearce" <spam@spam.com> wrote in message
news:4ddcce1b.591839525@news.eternal-september.org...
>>> NOPE, IF the host picks the remaining door he now has a 1/3 chance of
>>> the
>>> big prize, and the other two also have only a 1/3 chance each of the big
>>> prize, NOT 50:50.
>>
>>I should have added that yes IF (and only IF) the host reveals a goat,
>>the
>>other two will now have a 50:50 chance, but surely that is obvious, and
>>remains so whether they both switch or both stay, so is NO Longer like the
>>original MH problem at all.
>>
> Of course - and that is precisely the new scenario presented. As I
> said - re-read. And no, it is nothing like the original MH problem.

Why do I need to re-read, that is exactly what I said!!!!!!!!!!!!!!!!!
What the hell are you objecting to??????????????????

Trevor.

==============================================================================
TOPIC: What kills a valve rectifier?
http://groups.google.com/group/sci.electronics.repair/t/3452d3f8314c6ded?hl=en
==============================================================================

== 1 of 11 ==
Date: Tues, May 24 2011 3:42 am
From: "N_Cook"

Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is failed
both sides, 0 percent output . Inspecting the fuse it has failed at an end ,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast make/break
intermittant action of the fuse wire at an end , would that knock out an RR
valve? What in general happens in the failure of RRs ? I've only ever seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.

== 2 of 11 ==
Date: Tues, May 24 2011 4:04 am
From: "Arfa Daily"

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irg1t5$bvd$1@dont-email.me...
> Amp used for the first time, in 2 years of regular mains use, with a
> generator. Works fine with no problems. Coincidence ?, next gig back to
> usual mains supply, at power up, blows the mains fuse. The GZ34 is failed
> both sides, 0 percent output . Inspecting the fuse it has failed at an end
> ,
> not the central (T) section and otherwise complete wire shows no sag or
> discolouration. So possibly mechanical failure of fuse. If fast make/break
> intermittant action of the fuse wire at an end , would that knock out an
> RR
> valve? What in general happens in the failure of RRs ? I've only ever seen
> 75 percent , same as new, or 0 percent "goodness" at prescribed current
> settings of the Avo valve tester.
>
>

I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this down
to saggy filaments or whatever, where the valves are mounted horizontally,
or upside down.

Arfa

== 3 of 11 ==
Date: Tues, May 24 2011 4:38 am
From: "Phil Allison"

"Nutcase Kook "

>
> Amp used for the first time, in 2 years of regular mains use, with a
> generator. Works fine with no problems. Coincidence ?

** Spooky................

> next gig back to
> usual mains supply, at power up, blows the mains fuse.

** Noooooo...........

> The GZ34 is failed
> both sides, 0 percent output . Inspecting the fuse it has failed at an end
> ,
> not the central (T) section and otherwise complete wire shows no sag or
> discolouration. So possibly mechanical failure of fuse.

** Chemical fuses are notorious for that.

> If fast make/break
> intermittant action of the fuse wire at an end , would that knock out an
> RR
> valve?

** Rolls Royce do not make valves.

> What in general happens in the failure of RRs ?

** They " fail to proceed " ..................

> I've only ever seen
> 75 percent , same as new, or 0 percent "goodness" at prescribed current
> settings of the Avo valve tester.

** Well, you ain't seen nuthin' - pal.

..... Phil

== 4 of 11 ==
Date: Tues, May 24 2011 6:35 am
From: "N_Cook"

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:mhMCp.7026$Ky.3031@newsfe24.ams2...
>
>
> "N_Cook" <diverse@tcp.co.uk> wrote in message
> news:irg1t5$bvd$1@dont-email.me...
> > Amp used for the first time, in 2 years of regular mains use, with a
> > generator. Works fine with no problems. Coincidence ?, next gig back to
> > usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed
> > both sides, 0 percent output . Inspecting the fuse it has failed at an
end
> > ,
> > not the central (T) section and otherwise complete wire shows no sag or
> > discolouration. So possibly mechanical failure of fuse. If fast
make/break
> > intermittant action of the fuse wire at an end , would that knock out an
> > RR
> > valve? What in general happens in the failure of RRs ? I've only ever
seen
> > 75 percent , same as new, or 0 percent "goodness" at prescribed current
> > settings of the Avo valve tester.
> >
> >
>
> I've had a number of GZ34s fail short circuit, or suffer from serious
> flashover, and knock out fuses over the years, but I've always put this
down
> to saggy filaments or whatever, where the valves are mounted horizontally,
> or upside down.
>
> Arfa
>

What is the state of the fuse with a flashover? vapourised and blackened
fuse barrel presumably.

== 5 of 11 ==
Date: Tues, May 24 2011 10:16 am
From: "Arfa Daily"

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irgc22$ai2$1@dont-email.me...
> Arfa Daily <arfa.daily@ntlworld.com> wrote in message
> news:mhMCp.7026$Ky.3031@newsfe24.ams2...
>>
>>
>> "N_Cook" <diverse@tcp.co.uk> wrote in message
>> news:irg1t5$bvd$1@dont-email.me...
>> > Amp used for the first time, in 2 years of regular mains use, with a
>> > generator. Works fine with no problems. Coincidence ?, next gig back to
>> > usual mains supply, at power up, blows the mains fuse. The GZ34 is
> failed
>> > both sides, 0 percent output . Inspecting the fuse it has failed at an
> end
>> > ,
>> > not the central (T) section and otherwise complete wire shows no sag or
>> > discolouration. So possibly mechanical failure of fuse. If fast
> make/break
>> > intermittant action of the fuse wire at an end , would that knock out
>> > an
>> > RR
>> > valve? What in general happens in the failure of RRs ? I've only ever
> seen
>> > 75 percent , same as new, or 0 percent "goodness" at prescribed current
>> > settings of the Avo valve tester.
>> >
>> >
>>
>> I've had a number of GZ34s fail short circuit, or suffer from serious
>> flashover, and knock out fuses over the years, but I've always put this
> down
>> to saggy filaments or whatever, where the valves are mounted
>> horizontally,
>> or upside down.
>>
>> Arfa
>>
>
>
> What is the state of the fuse with a flashover? vapourised and blackened
> fuse barrel presumably.
>
>

Yes, vapourised

Arfa

== 6 of 11 ==
Date: Tues, May 24 2011 2:20 pm
From: Meat Plow

On Tue, 24 May 2011 11:42:05 +0100, N_Cook wrote:

> Amp used for the first time, in 2 years of regular mains use, with a
> generator. Works fine with no problems. Coincidence ?, next gig back to
> usual mains supply, at power up, blows the mains fuse. The GZ34 is
> failed both sides, 0 percent output . Inspecting the fuse it has failed
> at an end , not the central (T) section and otherwise complete wire
> shows no sag or discolouration. So possibly mechanical failure of fuse.
> If fast make/break intermittant action of the fuse wire at an end ,
> would that knock out an RR valve? What in general happens in the failure
> of RRs ? I've only ever seen 75 percent , same as new, or 0 percent
> "goodness" at prescribed current settings of the Avo valve tester.

If I pop a new valve back in, take some measurements and all seem
respectable, I don't try to dive further in and create scenarios in my
head as to the failure mode. UNLESS it comes back a few hours of usage
later with the same failure. However, after it is placed in a cabinet
I stress test all amps into a non-reactive 300 wrms 8 ohm resistor, one
of two I have mounted on a large heat sink from a CNC power supply. I use
a 400 hz tone and monitor the output adjusting the output until I see
just a taste of crossover distortion. I leave it this way until I can
smell and feel the amplifier/ output transformer, choke, mains
transformer etc get more hot than under normal use. Then it's tested
with a guitar and cabinet if it's just a head. I'm a musician so I have
those things laying around. I usually use my 4x12 Peavey cabinet for
amps that aren't combos. And a Fender 4x10 for Bass. I know what the
instruments should sound like though both cabinets with good amps.

--
Live Fast Die Young, Leave A Pretty Corpse

== 7 of 11 ==
Date: Tues, May 24 2011 2:25 pm
From: Meat Plow

On Tue, 24 May 2011 12:04:48 +0100, Arfa Daily wrote:

> "N_Cook" <diverse@tcp.co.uk> wrote in message
> news:irg1t5$bvd$1@dont-email.me...
>> Amp used for the first time, in 2 years of regular mains use, with a
>> generator. Works fine with no problems. Coincidence ?, next gig back to
>> usual mains supply, at power up, blows the mains fuse. The GZ34 is
>> failed both sides, 0 percent output . Inspecting the fuse it has failed
>> at an end ,
>> not the central (T) section and otherwise complete wire shows no sag or
>> discolouration. So possibly mechanical failure of fuse. If fast
>> make/break intermittant action of the fuse wire at an end , would that
>> knock out an RR
>> valve? What in general happens in the failure of RRs ? I've only ever
>> seen 75 percent , same as new, or 0 percent "goodness" at prescribed
>> current settings of the Avo valve tester.
>>
>>
>>
> I've had a number of GZ34s fail short circuit, or suffer from serious
> flashover, and knock out fuses over the years, but I've always put this
> down to saggy filaments or whatever, where the valves are mounted
> horizontally, or upside down.
>
> Arfa

What do you think about subbing the 5AR4 with a 5U4?

--
Live Fast Die Young, Leave A Pretty Corpse

== 8 of 11 ==
Date: Tues, May 24 2011 6:16 pm
From: "Arfa Daily"

"Meat Plow" <mhywattt@yahoo.com> wrote in message
news:pan.2011.05.24.21.25.01@emutt.macspoofer.lmao...
> On Tue, 24 May 2011 12:04:48 +0100, Arfa Daily wrote:
>
>> "N_Cook" <diverse@tcp.co.uk> wrote in message
>> news:irg1t5$bvd$1@dont-email.me...
>>> Amp used for the first time, in 2 years of regular mains use, with a
>>> generator. Works fine with no problems. Coincidence ?, next gig back to
>>> usual mains supply, at power up, blows the mains fuse. The GZ34 is
>>> failed both sides, 0 percent output . Inspecting the fuse it has failed
>>> at an end ,
>>> not the central (T) section and otherwise complete wire shows no sag or
>>> discolouration. So possibly mechanical failure of fuse. If fast
>>> make/break intermittant action of the fuse wire at an end , would that
>>> knock out an RR
>>> valve? What in general happens in the failure of RRs ? I've only ever
>>> seen 75 percent , same as new, or 0 percent "goodness" at prescribed
>>> current settings of the Avo valve tester.
>>>
>>>
>>>
>> I've had a number of GZ34s fail short circuit, or suffer from serious
>> flashover, and knock out fuses over the years, but I've always put this
>> down to saggy filaments or whatever, where the valves are mounted
>> horizontally, or upside down.
>>
>> Arfa
>
> What do you think about subbing the 5AR4 with a 5U4?
>
>
>

Never tried it, but looking at the specs, they look rather different from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

and

http://www.r-type.org/exhib/aaa0504.htm

The 5U4 appears to be able to handle more current, but at a lower max plate
voltage. Also, the heater requires substantially more current. Might be an
issue for the transformer supplying it ?

Arfa

== 9 of 11 ==
Date: Tues, May 24 2011 6:38 pm
From: "Phil Allison"

"Arfa Daily"
>
>> What do you think about subbing the 5AR4 with a 5U4?
>
>
> Never tried it, but looking at the specs, they look rather different from
> one another, see -
>
> http://www.r-type.org/exhib/aaa0997.htm
>
> http://www.r-type.org/exhib/aaa0504.htm
>

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the plates
and the cathodes - so there is a much bigger drop in voltage, more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.

..... Phil

== 10 of 11 ==
Date: Tues, May 24 2011 9:25 pm
From: spamtrap1888

On May 24, 6:38 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
> "Arfa Daily"
>
>
>
> >> What do you think about subbing the 5AR4 with a 5U4?
>
> > Never tried it, but looking at the specs, they look rather different from
> > one another, see -
>
> >http://www.r-type.org/exhib/aaa0997.htm
>
> >http://www.r-type.org/exhib/aaa0504.htm
>
> ** Useless info.
>
> The big difference between the 5AR4 and the 5U4 is in amount of voltage drop
> across each diode when conducting.
>
> The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
> and the voltage drop is very low, about 35 volts at 700mA peak.
>
> The 5U4 uses a directly heated cathode with lotsa space between the plates
> and the cathodes -  so there is a much bigger drop in voltage,  more like
> 100 volts at peak current.
>
> So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts DC
> straight off the B+.
>
> Also, the 5AR4 is rated to work reliably with a large filter cap on the
> cathodes ( 60 uF) compared to the 5U4 ( 40uF).
>
> So the proposed sub is bad news all around.
>

Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?

== 11 of 11 ==
Date: Tues, May 24 2011 10:28 pm
From: "Phil Allison"

"spamtrap1888"

Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?

**See:

http://www.guitaramplifierblueprinting.com/rectifiers.html

** Hard to find a single, technically correct statement in the whole blurb.

But that is what these loonies believe.

.... Phil

==============================================================================
TOPIC: GOOD STUDY METERIAL
http://groups.google.com/group/sci.electronics.repair/t/f752940733af7245?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, May 24 2011 6:20 am
From: SRAVANTHI LOVE

GOOD STUDY MATERIAL FOR KIDS
http://studymaterialforu.blogspot.com
UNIX INTERVIEW QUESTIONS
http://studymaterialforu.blogspot.com/2011/04/unix-interview-questions.html
JAVA INTERVIEW QUESTIONS
http://studymaterialforu.blogspot.com/2011/04/java-interview-questions.html
C ++ INTERVIEW QUESTIONS
http://studymaterialforu.blogspot.com/2011/04/c-interview-questions.html
CIVILS INTERCIEW QUESTIONS
http://studymaterialforu.blogspot.com/2011/04/civils-interview-questions-and-answers.html
DIGITAL LOGIC INTERCIEW QUESTIONS
http://studymaterialforu.blogspot.com/2011/04/digital-logic-design-interview.html
MICROPROCESSOR INTERVIEW QUESTIONS
http://studymaterialforu.blogspot.com/2011/04/microprocessor-interview-questions.html

==============================================================================
TOPIC: PC Power Supply Recommendations?
http://groups.google.com/group/sci.electronics.repair/t/5d9c672c7593977e?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, May 24 2011 7:53 am
From: Jeff Liebermann

On Mon, 23 May 2011 12:41:19 -0700 (PDT), KenO <kenitholson@yahoo.com>
wrote:

>"What I look for is power factor correction.  That will drop the
>efficiency somewhat, but is well worth it (and will soon be
>mandatory).
>Any idea when it will become mandatory?

In Europe, IEC 555-2 currently requires power factor correction to
reduce harmonics on power mains in power supplies. It's been around
for at least 15 years.

I don't know anything about the US status. Googling returned a muddle
which will require more time to untangle than I'm willing to burn.
Sorry(tm).

>"I forgot exactly what I used: <www.formfactors.org/developer/specs/
>ATX12V_PSDG_2_2_public_br2.pdf>
>Tried to use the link but only got "404. That's an error."

Very strange link. See ATX 2.2 link at:
<http://www.formfactors.org/FFDetail.asp?FFID=1&CatID=2>
The URL is a mix of / and \ in the path. That usually works, but not
this time. There are some links here:
<http://en.wikipedia.org/wiki/ATX#External_links>
which seem to work better. Here's my copy in case you can't get the
link to work:
<http://802.11junk.com/jeffl/crud/atx2_2.pdf>

>Do you know who makes the Dell PSU with the 120mm fan?

It won't work for building your own machine. The case has exactly one
120mm fan and it's not inside the power supply. It's near the bottom
of the case and acts as an air intake. The hot air gets blown out
through the power supply vent holes.
<http://img.villagephotos.com/p/2003-7/271271/Opt960%20Inside2.jpg>
The fan is the black thing above the disk drives. Air flow is from
left to right. There's no fan in the power supply.

More on PFC
<http://www.nist.gov/pml/quantum/power_121509.cfm>
<http://www.xbitlabs.com/articles/cases/display/atx-psu5.html>
This should explain power factor:
<http://www.xbitlabs.com/articles/cases/display/atx-psu5_3.html#sect0>
<http://www.silverstonetek.com/tech/wh_pfc.php>
More here:
<http://en.wikipedia.org/wiki/Power_factor>
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

==============================================================================
TOPIC: Wall Warts
http://groups.google.com/group/sci.electronics.repair/t/de407a5056a54ee0?hl=en
==============================================================================

== 1 of 6 ==
Date: Tues, May 24 2011 10:55 am
From: Puddin' Man

On Mon, 23 May 2011 20:24:18 -0400, "Wild_Bill" <wb_wildbill@XSPAMyahoo.com> wrote:

>The reply from whit is a good suggestion, but I suspect that the cells in
>the drill are shorted, which will damage a charging power supply. It seems
>that the old supply became overheated and failed, which will happen if the
>cells are shorted.
>I believe this is the reason for the substitute wall wart getting hot.

Certainly possible, for all I know.

I shoulda mentioned, I'm not an electronics guy, just a tinker. Limited
(make that -very- limited) skills, eqpt.

I might've charged with the new supply 20 min. before I noticed the heat.
The drill worked a little thereafter.

>To find out if the cells are shorted, the cells need to be accessed, and
>individually checked with an ohm meter or an instrument capable of measuring
>battery cell impedance or ESR.
>Also, a reading for individual cells with voltmeter reading of zero volts
>generally indicates shorted cells.

The drill still works a little. I measure about 4v aggregate from the
battery pack.

>Replacing all of the cells is the most effective solution, and cells with
>tabs can be soldered together in the original order, and restore full (or
>even better) operation of the drill (or most cordless tools).

The usual case, not practical. Wierd cell shapes, very old unit.

>If you have the ability to make good solder connections, replacement is
>usually less costly than paying someone else to do the work.
>
>There are numerous online sellers with reasonable prices for replacement
>cells.

If I can't tinker-fix it, it goes in the trash. Any replacement parts
either won't fit or are too expensive or both. I hate to throw
potentially useful tools away, but ...

Thanks,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

== 2 of 6 ==
Date: Tues, May 24 2011 11:22 am
From: spamtrap1888

On May 24, 10:55 am, Puddin' Man <puddingDOT...@gmail.com> wrote:
> On Mon, 23 May 2011 20:24:18 -0400, "Wild_Bill" <wb_wildb...@XSPAMyahoo.com> wrote:

> I shoulda mentioned, I'm not an electronics guy, just a tinker. Limited
> (make that -very- limited) skills, eqpt.
>
> I might've charged with the new supply 20 min. before I noticed the heat.
> The drill worked a little thereafter.
>
> >To find out if the cells are shorted, the cells need to be accessed, and
> >individually checked with an ohm meter or an instrument capable of measuring
> >battery cell impedance or ESR.
> >Also, a reading for individual cells with voltmeter reading of zero volts
> >generally indicates shorted cells.
>
> The drill still works a little. I measure about 4v aggregate from the
> battery pack.
>
> >Replacing all of the cells is the most effective solution, and cells with
> >tabs can be soldered together in the original order, and restore full (or
> >even better) operation of the drill (or most cordless tools).
>
> The usual case, not practical. Wierd cell shapes, very old unit.
>

> If I can't tinker-fix it, it goes in the trash. Any replacement parts
> either won't fit or are too expensive or both. I hate to throw
> potentially useful tools away, but ...
>

If the pack didn't consist of 8 AA-sized NiCds I would be muchly
surprised. Anybody who can plug new AAs into a remote control, and
knows which end of a soldering pencil to hold, likely has the skill
level to rebuild a battery pack.

== 3 of 6 ==
Date: Tues, May 24 2011 11:35 am
From: Jeff Liebermann

On Mon, 23 May 2011 15:54:46 -0500, Puddin' Man
<puddingDOTman@gmail.com> wrote:

>I've a Skil Mod 2375 3/8" cordless drill (9.6v) thats nearly an antique.

The charger was involved in a safety recall. I have a similar model
with the same problem. The xformer will overheat when trying to
charge a dead battery. If you call the 800 number, you might get a
free charger.
<http://www.all-cordless.com/skilrecalls.html>
However, if it's a later replacement, then all you did is blow the
thermal fuse inside the charger. You can crack it open and replace
it, but my guess(tm) is you also have some very dead batteries.

>Are there any guidelines for substituting these things? I'd like to keep the drill,
>but can hardly afford to burn the house down. :-)

Not without knowing where the charge controller (probably just a
resistor) is located. If it's inside the wall wart, you'll need to
add an identical resistor. If it's inside the drill, you can probably
get away with your 12VDC substitute. Measure the current drain at the
charger output. My guess(tm) is you should have a mess of AA size
NiCd batteries inside the drill, which are usually rated at 750ma-hr.
Using the 0.1C rule, that would be a charging current of about 75ma
max.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

== 4 of 6 ==
Date: Tues, May 24 2011 3:03 pm
From: Puddin' Man

On Tue, 24 May 2011 11:35:26 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote:

>On Mon, 23 May 2011 15:54:46 -0500, Puddin' Man
><puddingDOTman@gmail.com> wrote:
>
>>I've a Skil Mod 2375 3/8" cordless drill (9.6v) thats nearly an antique.
>
>The charger was involved in a safety recall. I have a similar model
>with the same problem. The xformer will overheat when trying to
>charge a dead battery. If you call the 800 number, you might get a
>free charger.
><http://www.all-cordless.com/skilrecalls.html>
>However, if it's a later replacement, then all you did is blow the
>thermal fuse inside the charger. You can crack it open and replace
>it, but my guess(tm) is you also have some very dead batteries.

Thanks. That was worth checking into.

They have no replacement parts for the 2375. They say that they'll
send paperwork so, if I send 'em the charger, they'll
send more paperwork so, if I buy a new Skil drill, they'll refund
$25 or somesuch -if- I send 'em the UPC code -and- the orig.
receipt, etc, etc ad nauseum. I don't think they really wanna
honor the recall.

>>Are there any guidelines for substituting these things? I'd like to keep the drill,
>>but can hardly afford to burn the house down. :-)
>
>Not without knowing where the charge controller (probably just a
>resistor) is located. If it's inside the wall wart, you'll need to
>add an identical resistor. If it's inside the drill, you can probably
>get away with your 12VDC substitute. Measure the current drain at the
>charger output.

Lost me there. Measure the *drain* at the charger output? But I'm
pretty sure it is inside the buggered charger.

>My guess(tm) is you should have a mess of AA size
>NiCd batteries inside the drill, which are usually rated at 750ma-hr.
>Using the 0.1C rule, that would be a charging current of about 75ma
>max.

It's evidently all original: charger is 92950, power pack is 92955,
and is a *sealed* unit. I see no way to take it apart.

Am I missing something here?

Thx,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

== 5 of 6 ==
Date: Tues, May 24 2011 9:28 pm
From: spamtrap1888

On May 24, 3:03 pm, Puddin' Man <puddingDOT...@gmail.com> wrote:
> On Tue, 24 May 2011 11:35:26 -0700, Jeff Liebermann <je...@cruzio.com> wrote:

> >My guess(tm) is you should have a mess of AA size
> >NiCd batteries inside the drill, which are usually rated at 750ma-hr.
> >Using the 0.1C rule, that would be a charging current of about 75ma
> >max.
>
> It's evidently all original: charger is 92950, power pack is 92955,
> and is a *sealed* unit. I see no way to take it apart.
>
> Am I missing something here?
>

The battery packs I've repaired consisted of two shells epoxied
together. Does this one not look like it could be knifed apart?

== 6 of 6 ==
Date: Tues, May 24 2011 10:36 pm
From: Jeff Liebermann

On Tue, 24 May 2011 17:03:17 -0500, Puddin' Man
<puddingDOTman@gmail.com> wrote:

>I don't think they really wanna
>honor the recall.

<http://www.cpsc.gov/cpscpub/prerel/prhtml03/03082.html>
Looks like the $25 rebate is all that they are offering.

Maybe calling them back and asking for the name of the company
attorney and whether this recall is defacto admission of their
responsibility if your garage burns down, might get their attention.

>>>Are there any guidelines for substituting these things? I'd like to keep the drill,
>>>but can hardly afford to burn the house down. :-)
>>
>>Not without knowing where the charge controller (probably just a
>>resistor) is located. If it's inside the wall wart, you'll need to
>>add an identical resistor. If it's inside the drill, you can probably
>>get away with your 12VDC substitute. Measure the current drain at the
>>charger output.
>
>Lost me there. Measure the *drain* at the charger output? But I'm
>pretty sure it is inside the buggered charger.

I guess it might be difficult to measure the current if the charger is
dead.

The problem is that we don't really know how the charging system works
without tearing it apart. If the blown charger has a resistor in
series with the output, there's no way to know at this point without
cracking it open, or comparing it with another working unit.

Start by using an ohms-guesser on the charger base. Cut the cord. Is
there DC continuity between the two wires and the contacts on the
charger base? If there's a measurable resistance, then the charger
base has either a resistor, or complexicated charge controller in the
base. I would therefore guess(tm) that the wall wart is just a simple
wall wart with nothing more complex than a thermal fuse inside.
However, if there is DC continuity between the leads and the battery
terminal connections, then the charge controller is inside the wall
wart, and a simple replacement isn't going to work.

Since the power supply is obviously blown and useless, tearing it
apart should reveal if there's anything inside. You'll probably find
a thermal fuse. If it's blown, just replace it with a similar thermal
fuse, glue the case back together, and continue charging. However, if
there's a series resistor inside (which is what I suspect), then use
the 12V adapter, add a similar resistor in series, measure the
charging current, and see if it's reasonable 0.1C. If not, adjust the
resistor value for 0.1C charging current.

>>My guess(tm) is you should have a mess of AA size
>>NiCd batteries inside the drill, which are usually rated at 750ma-hr.
>>Using the 0.1C rule, that would be a charging current of about 75ma
>>max.
>
>It's evidently all original: charger is 92950, power pack is 92955,
>and is a *sealed* unit. I see no way to take it apart.
>
>Am I missing something here?

Most chargers and charging bases are solvent welded together. They
can usually be cracked open with brute force. Place a masons chisel
along the glue line, and beat on it with a hammer. The glue line
should crack as the plastic bends. If not, just use a hack saw to saw
along the glue line. Do the repair, and then glue the case back
together.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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==============================================================================

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