sci.electronics.repair@googlegroups.com

Today's topics:

* Contactor coil: 50 Hz vs. 60 Hz - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/0d1a06068779ce43?hl=en
* Dark strip on LCD... - 4 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/131fd0ca19572f97?hl=en
* Yellow Glue strikes again - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/9d8bded3db582b06?hl=en
* SPAM -- ELECTRONICS REPAIR PROBLM SOLVING MATHOD - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/5aa00cfd22c7e05d?hl=en
* Tips How to Reinstall P4 CPU & Heat Sink or Separate P4 CPU from Heat Sink? -
1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/707e8e7589f93af2?hl=en
* The nuts are becoming dominant - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/b6dfa94787754a55?hl=en

==============================================================================
TOPIC: Contactor coil: 50 Hz vs. 60 Hz
http://groups.google.com/group/sci.electronics.repair/t/0d1a06068779ce43?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Sep 7 2011 10:33 am
From: Jamie

ehsjr wrote:
> NT wrote:
>
>> On Sep 2, 8:41 pm, John Fields <jfie...@austininstruments.com> wrote:
>>
>>> Snipped a lot of repetitious, self serving nonsense.
>>>
>>>
>>>>>>> and if the relay is
>>>>>>> designed to operate on AC with a certain RMS current in its coil,
>>>>>>> how
>>>>>>> can it possibly overheat if that current is DC?
>>>
>>>
>>>>>> With the same current it wont, with higher curren ti will. IIRC you
>>>>>> proposed using 174v rms,
>>>
>>>
>>>>> No, I merely added a capacitor across the output of _your_ proposed
>>>>> full wave rectified 120 VRMS 60Hz source (170V peak) in order to get
>>>>> smoothed DC closer to the relay's must-make current.
>>>
>>>
>>>> fwliw I said use diodes, you came back with a FW BR. I dont think it
>>>> matters.
>>>
>>>
>>> ---
>>> Then show me your circuit.
>>>
>>> Just in case you've forgotten, your suggestion was to use a 240V AC
>>> relay using diodes and 120V mains.
>>> ---
>>>
>>>
>>>>>> that would be ok on your specific relay, but
>>>>>> not a universal solution.
>>>
>>>
>>>>> ???
>>>
>>>
>>>> Your proposd BR+C delivers the right i for one specific relay. For
>>>> some relays it will fry them.
>>>
>>>
>>> ---
>>> Show me.
>>
>>
>>
>> If you want to go get some specs of other relays, you can. This is
>> starting to get silly.
>
>
> Worth investigating, to me. JF gave a specific relay & numbers. I
> tried to find a relay to support the idea that an AC/DC relay would
> be happy with DC voltage about 50% of AC rating. Can you please
> provide a reference?
>
> Meanwhile, what I did find was an ap note from Tyco entitled
> "Operating DC Relays from AC and Vice-Versa" .
> http://relays.te.com/appnotes/app_pdfs/13c3250.pdf
>
> It does not agree with the DC at ~50% of AC rating idea. It uses
> the example of a KR series relay coil. Their example uses a 12
> volt AC relay fed by DC. The example states that the "DC voltage
> cannot exceed 9.8 volts", and "should not be lower than 7.35 volts".
> Thus the DC range would be ~61%(minimum) to ~81% (maximum) of the
> 12VAC rating.
>
> Extrapolating, it does agree with the idea of BR+C fed by 120 for
> the 240 volt relay, insofar as the DC voltage:
> ~146VDC min to ~194VDC max, which makes the midpoint ~170VDC.
> That's very close to ~168 from the BR+C
>
> Regarding coil ratings, I've worked with DC relays, and I've worked
> with AC relays, but I haven't worked with AC/DC coil relays, so
> I can't speak from experience with them, and I haven't found
> anything yet specifically dealing with that, other than the
> link I found to Tyco. So a specific link or links would be
> most helpful.
>
> Thanks,
> Ed
You must remember that AC coil relays are wound a little different,
its not just induction here. Inter pole windings help keep the AC coil
from chattering the armature. I am sure under DC operation, this may
effect the calculations.

There are some AC coil relays that do not do this and thus the 50%
voltage for DC should come close, but then again, DC R in the coil also
plays a role in this.

Jamie

==============================================================================
TOPIC: Dark strip on LCD...
http://groups.google.com/group/sci.electronics.repair/t/131fd0ca19572f97?hl=en
==============================================================================

== 1 of 4 ==
Date: Wed, Sep 7 2011 1:34 pm
From: "Deke"

TV is a Polaroid 42" 1080p LCD, model TLX-04244B.
It was purchased on 11/28/08, at Wal-Mart, with an extended warranty.
It has developed a horizontal dark strip, about 3 inches wide, about 1/4 of
the way down on the screen, running from one side of the screen to the
other. A technician from the insurance company is coming to check it out on
the 13th of this month.
I think one of the backlights has failed. Is it repairable?

TIA!

Picture of the Day http://apod.nasa.gov/apod/

== 2 of 4 ==
Date: Wed, Sep 7 2011 1:58 pm
From: Sparky

> TV is a Polaroid 42" 1080p LCD, model TLX-04244B.
> It was purchased on 11/28/08, at Wal-Mart, with an extended warranty.
> It has developed a horizontal dark strip, about 3 inches wide, about 1/4 of
> the way down on the screen, running from one side of the screen to the
> other. A technician from the insurance company is coming to check it out on
> the 13th of this month.
> I think one of the backlights has failed. Is it repairable?
>
> TIA!

*Anything* is repairable. Is it economically worth it? Only your insurance
company can tell you. ;-)

It's probably not a backlight. Can you see video in the dark band (look very
closely -- shine a bright flashlight at the area to help you see)? If the
backlight has failed you should still be able to see video in that dark band.
If not...

Your LCD display is probably bad. The display is made up of wide bands (about
3" -- depends on the model) running horizontally and vertically. Each of
those areas is controlled by a driver IC. If one of the driver ICs fail you
get a dark or light band (horizontal or vertical).

This PDF has some symptoms, causes, and fixes:

<http://preher-
tech.com/Documents/LCD%20TV%20Display%20failure%20symptoms%20and%20possible%20
causes.pdf>

== 3 of 4 ==
Date: Wed, Sep 7 2011 2:02 pm
From: "Deke"

"Sparky" <see@thesig.net> wrote in message
news:0001HW.CA8D291200228F8EB01029BF@news.eternal-september.org...
>> TV is a Polaroid 42" 1080p LCD, model TLX-04244B.
>> It was purchased on 11/28/08, at Wal-Mart, with an extended warranty.
>> It has developed a horizontal dark strip, about 3 inches wide, about 1/4
>> of
>> the way down on the screen, running from one side of the screen to the
>> other. A technician from the insurance company is coming to check it out
>> on
>> the 13th of this month.
>> I think one of the backlights has failed. Is it repairable?
>>
>> TIA!
>
> *Anything* is repairable. Is it economically worth it? Only your insurance
> company can tell you. ;-)
>
> It's probably not a backlight. Can you see video in the dark band (look
> very
> closely -- shine a bright flashlight at the area to help you see)? If the
> backlight has failed you should still be able to see video in that dark
> band.
> If not...
>
> Your LCD display is probably bad. The display is made up of wide bands
> (about
> 3" -- depends on the model) running horizontally and vertically. Each of
> those areas is controlled by a driver IC. If one of the driver ICs fail
> you
> get a dark or light band (horizontal or vertical).
>
> This PDF has some symptoms, causes, and fixes:
>
> <http://preher-
> tech.com/Documents/LCD%20TV%20Display%20failure%20symptoms%20and%20possible%20
> causes.pdf>
>

Yes, video is visible in the dark area, its only about half as bright as the
rest
of the screen. In dark scenes its not noticeable, but on light screens its
easy to see it.

== 4 of 4 ==
Date: Wed, Sep 7 2011 2:08 pm
From: "Deke"

"Sparky" <see@thesig.net> wrote in message
news:0001HW.CA8D291200228F8EB01029BF@news.eternal-september.org...
>> TV is a Polaroid 42" 1080p LCD, model TLX-04244B.
>> It was purchased on 11/28/08, at Wal-Mart, with an extended warranty.
>> It has developed a horizontal dark strip, about 3 inches wide, about 1/4
>> of
>> the way down on the screen, running from one side of the screen to the
>> other. A technician from the insurance company is coming to check it out
>> on
>> the 13th of this month.
>> I think one of the backlights has failed. Is it repairable?
>>
>> TIA!
>
> *Anything* is repairable. Is it economically worth it? Only your insurance
> company can tell you. ;-)
>
> It's probably not a backlight. Can you see video in the dark band (look
> very
> closely -- shine a bright flashlight at the area to help you see)? If the
> backlight has failed you should still be able to see video in that dark
> band.
> If not...
>
> Your LCD display is probably bad. The display is made up of wide bands
> (about
> 3" -- depends on the model) running horizontally and vertically. Each of
> those areas is controlled by a driver IC. If one of the driver ICs fail
> you
> get a dark or light band (horizontal or vertical).
>
> This PDF has some symptoms, causes, and fixes:
>
> <http://preher-
> tech.com/Documents/LCD%20TV%20Display%20failure%20symptoms%20and%20possible%20
> causes.pdf>
>

Case 18 is similar, but not vertical, horizontal.

==============================================================================
TOPIC: Yellow Glue strikes again
http://groups.google.com/group/sci.electronics.repair/t/9d8bded3db582b06?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Sep 7 2011 1:42 pm
From: dewar

On Aug 30, 8:59 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
> ** I had hoped that the dreaded Yellow Glue peril had gone away - but it is
> still with us.
>
> Most of you will have seen it holding parts down to PCBs on Asian made
> equipment and many of those will have seen what happens if the parts
> involved get hot.
>
> The example on my bench is the SMPS from an Alesis powered monitor ( M1
> Active, Chinese made) ) which has blown up big time because of the damn
> Yellow Glue used to secure a ferrite toroidal coil.  All the glue used had
> gone brown or back ( ie carbonised ) on this coil and arced across nearby
> tracks taking out the main switching MOSFET, its drive IC and associated
> transistors, high speed diodes and even the AC bridge rectifier diodes.
>
> The toroidal coil had to be un-wound, cleaned up and re-wound. The same glue
> was attacking parts elsewhere on the board too ( it corrodes copper) and had
> to be laboriously scraped off.
>
> Are the dickheads who squirt this horrible goop all over PCBs  NEVER  going
> to wake up ??
>
> .....  Phil

Sony had a problem with this glue on broadcast video recorders years
ago. Their tech bulletin blamed "CHLOROPRENE GLUE". One current mfr
data sheet shows a reduction in resistance from 10^13 to 10^8 after
500 hours at 100C. Unfortunately, the resistance just keeps dropping
after that.

==============================================================================
TOPIC: SPAM -- ELECTRONICS REPAIR PROBLM SOLVING MATHOD
http://groups.google.com/group/sci.electronics.repair/t/5aa00cfd22c7e05d?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Sep 7 2011 3:15 pm
From: JeffM

x-no-archive: Yes
Evan Platt wrote:
>My God, where did you learn to spell, idiot spammer?
>
Judging from the header:
NNTP-Posting-Host: 180.178.4.146

that would be India.
route: 180.178.0.0/19
descr: Unitech Wireless (Tamilnadu) Pvt. Ltd.
origin: AS23870
mnt-by: MAINT-UNITECH-WIRELESS-IN
changed: varinder.singla@ uninor.in 20100930

You might want to contact his provider and bitch at them
--but, with as much crap as 123maza continues to post,
it would be naive to expect
that his provider is any less rogue than he is.

Everyone else using Usenet has learned to ignore his posts
and just let them fall off the bottom of the list
or has blacklisted his nyms/domain.
You, OTOH, seem to be a bit slow on the pickup.

Another point about posting to Usenet:
If you recognize something as spam
yet just can't resist the urge to respond to it,
add SPAM (all caps) to the Subject line
so that others can filter out your idiocy.

==============================================================================
TOPIC: Tips How to Reinstall P4 CPU & Heat Sink or Separate P4 CPU from Heat
Sink?
http://groups.google.com/group/sci.electronics.repair/t/707e8e7589f93af2?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Sep 7 2011 3:45 pm
From: KenO

Hi G²,

"You  have no choice but to separate the heat sink and processor so
you can release the lock lever on the socket. I would warm the heat
sink up with a hair dryer which will likely soften up the thermal
'adhesive' so yo can pry it apart. It is IMPERATIVE that you do not
put any force  between any layers of the processor as that will
destroy it. An Xacto knife or razor blade between the processor top
and the heat sink can crack it loose."

Thanks for the tip!

"BTW why did you want to pull the heat sink?"

It was accidental I needed to get to the P4 Heat Sink Retainer and
thought the Heat Sink would just pop off when pulled up on it.

Instead I pulled off the Heat Sink and P4 CPU!!!

So may have already killed it?

"I have removed heat sinks more times than I can remember usually for
installing a faster processor. When I release the heat sink retainer
clamp I rotate the heat sink a little to get it loose as the thermal
pad on the sink can be a little stubborn."

Agree the Dell 2350 adhesive seems like a black rubber? Have you had
any experience with it?

Thanks again for your help!

Ken

==============================================================================
TOPIC: The nuts are becoming dominant
http://groups.google.com/group/sci.electronics.repair/t/b6dfa94787754a55?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Sep 7 2011 3:57 pm
From: "Charles"

Poor signal to noise ratio, lately. Sad to see as this usenet group has
(had?) a lot to offer.

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