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On Jan 5, 2021, at 17:30, Bruce Atwood <CCDman1@...> wrote:

My new (to me) s/n B041515 7904 arrived DOA. (ebay, "not working, for parts".) With the help of my mostly trusty DSO138 I found the shorted 47/25V dipped tantalum on the -15 supply. Replaced it with a 470/25V aluminum electrolytic, 'cause that's what I had. It now has a beautiful and bright trace. I have ordered what I hope is an original paper manual for the early 7904s. The read outs do not work and all the manuals I have found online are for the later version, s/n B26000 and up. While waiting for USPS is there a downloadable version of the early manual somewhere? Point me to it please. thanks
PD I'm in the market for a 7A19 and a 7A26, any advice welcome.

Re. recapping 2465B

Youre on the cusp of learning the *hard way* why advice to
NOT replace caps is extremely bad.

Out of the multiples of semi load after semi load of equipment
I worked on "back in the day" (very high volume consumer electronics
from tube to fine pitch SMT)Ive seen too many electrolytics and some
tantalums go 'knees up'
and leak, explode, literally take off like rockets and stick in a ceiling 8
feet up,
blow confetti across the room, destroy power supplies and even
turn power transformers into smoking piles of tar and iron.

And do circuit board damage...

Only a* FOOL* thinks they can get away with NOT recapping
and I do mean ALL of the caps. Its a crap shoot, a losing gamble
to trust any old cap.

Its a false Meme from the antique radio world that says
"I can get away with not replacing caps/ just testing them"

That Meme is from the world of working on an old AM broadcast or SW
receiver and attempting to keep it as near "stock " as possible.
The adventurous remove old caps and hide new ones inside.
The foolish ignore old caps...

Its EXTREMELY bad practice in anything worth keeping, such as high
end equipment like Tek.

Its a second Fools Errand and false meme to play the "bring it up on a
variac"
or "Ill reform a 50 year old cap." Delusional. The "bring it up on a
variac" meme was
for finding shorts that were hiding in equipment with linear power supplies
where just turning the thing on instantly blew the fuse. It is NOT a valid
or useful procedure for dealing with old caps, no matter how hard the
True Believers want it to be.

Ignore those advising anything but a total recap. *They wont be paying for
the damage their foolish advice causes.*

This is (presumably) high end, near scientific Tek (and other) test
equipent. If its not
worth $100 in caps and a days work, why bother? Just throw it in the
dumpster.

Signed, replaced more leaky, shorted and open caps than " theyll" see in 5
lifetimes...,

Hey Guys,

I'm in the process of (mostly done I think) repairing a 7904 power supply that goes into pulse mode. I replaced a number of the bad tantalums on the cap rectifier board which brought some supplies closer to where they needed to be but but did not keep the supply from going into pulse mode. Continuing to diagnose things I found that pulling C1511 on the LV regulator board solved the problem, however the cap I pulled isn't reading as a short and replacing with a known good causes the pulse mode to return. C1511 seems to be working as a speed up capacitor for the regulator (allowing high frequency transients to bypass R1514 in the ladder) but seems awful high at 0.1 uF for that purpose. I'm considering replacing with a much smaller value ceramic (like 100 pF). Does anyone have any experience/thoughts/suggestions with this? Could my -50V supply have a lot of noise on it from somewhere else that it shouldn't which is causing this cap to be a problem? I'm currently running the supply into a bank of resistive loads so it would have to come from a connection to one of the other supplies if this was the case.

Thanks for the help.
Ricky

Re. recapping 2465B

Youre on the cusp of learning the *hard way* why advice to
NOT replace caps is extremely bad.

Out of the multiples of semi load after semi load of equipment
I worked on "back in the day" (very high volume consumer electronics
from tube to fine pitch SMT)Ive seen too many electrolytics and some
tantalums go 'knees up'
and leak, explode, literally take off like rockets and stick in a ceiling 8
feet up,
blow confetti across the room, destroy power supplies and even
turn power transformers into smoking piles of tar and iron.

And do circuit board damage...

Only a* FOOL* thinks they can get away with NOT recapping
and I do mean ALL of the caps. Its a crap shoot, a losing gamble
to trust any old cap.

Its a false Meme from the antique radio world that says
"I can get away with not replacing caps/ just testing them"

That Meme is from the world of working on an old AM broadcast or SW
receiver and attempting to keep it as near "stock " as possible.
The adventurous remove old caps and hide new ones inside.
The foolish ignore old caps...

Its EXTREMELY bad practice in anything worth keeping, such as high
end equipment like Tek.

Its a second Fools Errand and false meme to play the "bring it up on a
variac"
or "Ill reform a 50 year old cap." Delusional. The "bring it up on a
variac" meme was
for finding shorts that were hiding in equipment with linear power supplies
where just turning the thing on instantly blew the fuse. It is NOT a valid
or useful procedure for dealing with old caps, no matter how hard the
True Believers want it to be.

Ignore those advising anything but a total recap. *They wont be paying for
the damage their foolish advice causes.*

This is (presumably) high end, near scientific Tek (and other) test
equipent. If its not
worth $100 in caps and a days work, why bother? Just throw it in the
dumpster.

Signed, replaced more leaky, shorted and open caps than " theyll" see in 5
lifetimes...,

Hi EJP,

You are probably not missing much by not having the tracking
information. USPS tracking has been virtually useless for months.
Since April or May as I recall one simply sees a couple of steps in the
shipping process and then a departure from the last station Then days
after days of no further reports since it left Podunk or wherever.
Podunk may be only 150 miles away but no new statuses are reported for
days on end. It is more of a frustration than a help.

Jack

On 1/3/2021 9:48 PM, EJP wrote:

Dennis

Rather than create more work for yourself with tracking, why not just
scan the ticket and upload it here so people can find their own
tracking numbers? I always like to have this information anyway, not
just for overdue mail, so I can track it in and know what day it will
arrive.

Just a thought.

EJP