sci.electronics.repair@googlegroups.com

Today's topics:

* EDC 521 DC calibrator blowing fuses - 2 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/5fd358d9fe0d0a0c?hl=en
* Nikko Alpha 220 - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/6d4cff546b52714e?hl=en
* The common ThinkPad powerup problem - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/9730825a5202a5fd?hl=en
* Tube Amp 6L6GC Valve Peavey Mace VT Guitar Amplifier - 3 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/9ad57064b3ab9e7f?hl=en
* How to find semiconductor replacements? - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/dcb181e80eb71a20?hl=en
* Arcam amp ... - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/7cc228c388c21ebf?hl=en
* Proview 986M 19" monitor fixed - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/dd7c6160c5c07e36?hl=en

==============================================================================
TOPIC: EDC 521 DC calibrator blowing fuses
http://groups.google.com/group/sci.electronics.repair/t/5fd358d9fe0d0a0c?hl=en
==============================================================================

== 1 of 2 ==
Date: Thurs, Feb 17 2011 4:17 pm
From: Jamie

Jim Yanik wrote:

> "N_Cook" <diverse@tcp.co.uk> wrote in
> news:ijj5kg$3bn$1@news.eternal-september.org:
>
>
>>JW <none@dev.null> wrote in message
>>news:35upl6lr8suad9btcu6jskug49oel94vod@4ax.com...
>>
>>>Here's one I haven't seen before. Bought an EDC (now Krohn-hite) 521
>>>DC calibrator on the surplus market that was blowing fuses. There
>>>were two power supplies that seemed to be causing the problem +-150V.
>>>Turns out that there were two 22K 2W carbon comp resistors that are
>>>used as bleeders across the two 470uF filter caps. Both had changed
>>>resistance - one was about 2K, the other was 150 ohms! I've seen
>>>carbon comps drift, but never saw ones that drifted *that* far. Also,
>>>in circuits like this where they are dissipating over a watt, they
>>>usually drift high; at least in my experience...
>>>
>>>Well, after replacement it seems to be working well. May need a
>>>calibration though.
>>
>>
>>If you still have them , try a neat 0.5mm thick Dremmelgrinding disc
>>cut across the middle and see if there is a gradation of resistance
>>developed across the material , and so along the length. Just under
>>the surface coating you may find the high conductivity path.
>>I keep a "black museum" of such oddities , don't know if anyone else
>>does
>>
>>
>>
>>
>>
>
>
> I used to see 2W carbon comp resistors change values drastically all the
> time in TEK 520 and 520A vectorscopes. I believe it's heat-related.
> (it also might depend on how much V drop across them)
>
> They used to char the PCB even with a 1/2" standoff spacing and some even
> dropped off the PCB.
>
>

Electronics isn't fun unless you have some flames, forehead contact with
debris, and escaping blue smoke!

Jamie

== 2 of 2 ==
Date: Thurs, Feb 17 2011 4:29 pm
From: dplatt@radagast.org (Dave Platt)

> I used to see 2W carbon comp resistors change values drastically all the
> time in TEK 520 and 520A vectorscopes. I believe it's heat-related.
> (it also might depend on how much V drop across them)
>
> They used to char the PCB even with a 1/2" standoff spacing and some even
> dropped off the PCB.

Sounds as if they used a bunch of recycled SWTPC Tigersaurus power
amplifier PCBs to make those vectorscopes (or, possibly, a couple of
recycled SWTPC designers).

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

==============================================================================
TOPIC: Nikko Alpha 220
http://groups.google.com/group/sci.electronics.repair/t/6d4cff546b52714e?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Feb 17 2011 5:03 pm
From: "Mark Zacharias"

"Tim Schwartz" <tim@bristolnj.com> wrote in message
news:ijji70$gam$1@news.eternal-september.org...
> Hello all,
>
> I've got a Nikko Alpha 220 power amp here, and need to know the value of
> R751/752/753/754. I'm pretty sure they are all the same value. If
> someone has a service manual or schematic to share, that would be terrific
> too.
>
> Regards,
> Tim Schwartz
> Bristol Electronics

Eserviceinfo.com has a 440 manual - maybe that is similar?

Mark Z.

==============================================================================
TOPIC: The common ThinkPad powerup problem
http://groups.google.com/group/sci.electronics.repair/t/9730825a5202a5fd?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Feb 17 2011 5:03 pm
From: D Yuniskis

Hi Adrian,

On 2/17/2011 4:07 PM, Adrian C wrote:
> On 17/02/2011 22:35, D Yuniskis wrote:
>>
>> Since this is such a common remedy for ThinkPads,
>> I started wondering what the actual *reason* (cause)
>> behind it might be.
>
> Try here
>
> <http://forums.lenovo.com/t5/T61-and-prior-T-series-ThinkPad/T23-won-t-power-up-with-good-battery/m-p/230682>
> and also the thinkpads forum.
> http://forum.thinkpads.com/viewtopic.php?f=28&t=87401
>
> Some good speculation & answers given :)

Thanks, but these describe a different type of problem(s).

Each time I have encountered a "powerup problem" on a
thinkpad, the symptoms have been:

Disk light flashes (less than one second) when power
button is pressed -- no other activity is noticed.
A second press gives the same result. Holding
power button *down* makes no difference, etc.

The behavior is the same whether plugged into AC
power or running on battery.

If you unplug the unit, remove the battery pack
and lean on the power button for a while (I hold it
for 20 seconds) and *then* plug in the AC power, it
boots right up and runs WITHOUT PROBLEM for hours/days.
You can then install the battery while it is running.
Then, disconnect power. Etc. I.e., the battery is
fine, the AC adapter is fine, the laptop itself is
fine (once it has powered up).

BIOS is at the latest revision, etc.

It is as if something has a charge on it that must be
dissipated before the normal reset/startup will work.
I seem to recall this behavior often begins when the
laptop has been left on AC power (yet powered *off*)
for a prolonged period. I will start noting the various
conditions in which the problem presents itself.

>> Which prompted a web search for a schematic (so I
>> can see what *might* be going on when this happens).
>> Of course, no luck on that score...
>
> I have a schematic for the similar T23 I could mail you.

What's the difference between T23 and T22 (I guess I can
go googling... :> )

Thx,
--don

==============================================================================
TOPIC: Tube Amp 6L6GC Valve Peavey Mace VT Guitar Amplifier
http://groups.google.com/group/sci.electronics.repair/t/9ad57064b3ab9e7f?hl=en
==============================================================================

== 1 of 3 ==
Date: Thurs, Feb 17 2011 5:05 pm
From: "Phil Allison"

"Meat Plow the FUCKWIT "
>
>>> Could refit with two EL34s.
>>
>> ** Make any issues worse not better.
>>
>>> My Musicman 112 combo uses a pair of Mullards at around 700v plate.
>>
>> ** And only half that voltage on the screens.
>>
>> Not relevant at all - fuckhead.
>
> It's very relevant,

** Get stuffed.

> Any moron knows you wouldn't
> just drop a pair of EL34s in without some slight modification.

** Total red herring.

..... Phil

== 2 of 3 ==
Date: Thurs, Feb 17 2011 5:41 pm
From: "Arfa Daily"

"Fred" <nobody@home.com> wrote in message
news:Xns9E8F934CEDD51nobodyhomecom@74.209.131.13...
> "Phil Allison" <phil_a@tpg.com.au> wrote in news:8s4emqFgqmU1
> @mid.individual.net:
>
>>
>> "Fred the Fuckwit "
>>>
>>>
>>> Hmm....I don't think this is a good idea. These amps are built really
>>> cheap with common cathode bias,
>>
>>
>> ** No they are not.
>>
>> Strictly grid bias.
>>
>> You trolling imbecile.
>>
>>
>>
>>
>> .... Phil
>>
>>
>>
>>
>
> Geez, Phil, asshole....thanks!
>
> Assholes like you is the reason someone who comes here gets no help....

Well, that's a bit unfair on the rest of us ...

Arfa

== 3 of 3 ==
Date: Thurs, Feb 17 2011 6:47 pm
From: Jeff Urban

It's obvious you are looking for that sweet distortion at a lower
level. Whether the reason is to avoid a visit by the cops, or that the
speakers can't handle all the output doesn't matter.

One option is a power soak. These are just banks of high wattage
resistors in a box with switches to configure them for different
amounts of attenuation. This option removes the interaction between
the tubes/output transformer and speaker(s). For the purist, this
interaction is part of the sweet sound and is important.

Of course if you have to have it all that is not good enough. You have
options. Use a lower capacity speaker system to start with. The VC and
output Xfmr interaction is part of the cone excursion of the speaker.
To the amp is looks like saturation in a way, but it's not quite the
same. Much has been devoted to this and I am not prepared to go into
seventy years of history. But decoupling the VC from the amp will not
get you the same sound. Also, running the amp at a lower power will
never saturate the output transformer core, but eh, we do the best we
can.

Actually the best way one might think is to somehow reguilate the
plate voltage down. Doesn't matter voltage or current. But there is
another way. This will get you closest to what you want. I really
don't know how it will affect the output tubes, but I can guarantee
they won't overheat.

Lower the G2 voltage. Now if the amp is grid biased you will have to
adjust that, but if it is cathode biased it will adjust itself.
However, being familiar with cathode stripping in CRTs, I can't say it
won't happen to the output tubes. I don't THINK it's a big concern,
but don't take that to the bank.

The lower G2 (screen grid) voltage makes the tube behave more like a
triode. Thus it's output impedance is higher. This allows every
abberant change in current drawn by the load to interact. You could
literally have a switch on the back. If the outputs are cathode
biased, it should work just fine. Flip it one way for low power and
the other for high. If you're concerned about cathode stripping there
are two options. One is a simple megohm resistor in series with each
G1. To get fancy you could use a diode with the anode connected to the
control grid (G1). If you use the diode put about a ten meg across it,
no tube is perfect. But you do this separately for each of the six
tubes.

I think a one meg, or even a 2.2 meg would work just fine. In fact you
can go as high as you want until the interelectrode capacitance comes
into play. Always use a scope, because it could be oscillating. You
don't want that.

I don't think cathode stripping is the issue, but the operative word
here is think. Nobody wants to wreck $100+ worth of pentodes.

JURB

==============================================================================
TOPIC: How to find semiconductor replacements?
http://groups.google.com/group/sci.electronics.repair/t/dcb181e80eb71a20?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Feb 17 2011 5:14 pm
From: "Phil Allison"

"Charles the Expert"
>
> JEDEC part numbers used to mean something for discrete devices, now they
> relate more to memory devices (ICs) and the like.

** Huh ???

>> JEDEC still suggests package outlines, but they appear to have backed off
> from other details that used to help repair technicians select reasonable
> replacements for solid state devices.

** Do tell us more.

> The 1N, 2N, 3N system is now officially dead?

** Plenty on sale last time I looked.

( Wot is this wanker on ??? )

.... Phil

==============================================================================
TOPIC: Arcam amp ...
http://groups.google.com/group/sci.electronics.repair/t/7cc228c388c21ebf?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Feb 17 2011 5:43 pm
From: "Arfa Daily"

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ijjhae$8fn$1@news.eternal-september.org...
> Arfa Daily <arfa.daily@ntlworld.com> wrote in message
> news:uzc6p.13691$Ga7.9010@newsfe16.ams2...
>> Anyone by any chance got schematics for an Arcam Alpha 10 amplifier ?
>>
>> TIA
>>
>> Arfa
>
>
> Not motorized function sw prob I hope.
>
>

No, it's not. But why do you ask, I wonder ? I did one of those on an Alpha
9 just yesterday. It was no particular problem, as has been the case with a
few I've done in the past.

Arfa

==============================================================================
TOPIC: Proview 986M 19" monitor fixed
http://groups.google.com/group/sci.electronics.repair/t/dd7c6160c5c07e36?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Feb 17 2011 11:39 pm
From: JR North

Replaced C635 10uf 250V . Monitor back up-runs fine. I know-a cap; big
deal. But since I'm not an electronics whiz kid, resurrecting this
thing 3 times since new makes me feel kinda good.
JR

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