Electronics > Repair
HP34401A: Just bought one. Do I need to change the caps?
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IDontKnow:
While I totally agree not to touch running systems more than necessary: My one and only HP mixed signal oscilloscope (from the late 90s) just broke due to a single failing tantalum capacitor - the same variety that can be found in the HP34401A. Very annoying. Very frustrating when it happens.

So I will swap the Tantals in the HP34401A.

I had failing Tantals (burning or blowing up) in other test gear from the 80s and 90s occasionally. I agree that they fail much less than some think - but they do sometimes fail. In my W&G signal generator each and every tantalum was secured by a small series resistor (100R) that blew with the tantalum.
And three tantalums blew there up to know.

Not a bad idea to change them every 30 years or so.  Especially in the case of HP34401A they are super easy to change.

My first post here. Very nice content and company on this web site, I have to say.

Gerd.
coromonadalix:
had 3x 34401a,  i measured the supply lines for any problems

only one who had an very dim vfd, i recapped this one,  removed chemicals and tants,  redone completly, new clone vfd,   sent to cal lab with flying colors, still in specs

others 2  where fine, EDIT  oh yeah  one had a defective x-former (wrong voltage put on it)  and in specs too,   no recapping

some say  don't change, some say change them,  i would say :  evaluate and test before ...  if the supply lines are noisy ....

if you are not well equipped, or have experience with smd   be careful, damage can be done pretty easily  ...
iMo:
Mine is 1999, US made, I replaced the original 4 big elyts this spring, the old ones did not leak and afaik were still good.
IanJ (IanScottJohnston) advices in his great YT repair vids to replace the 4x or 5x 22u/25V yellow tantalum bricks with 22u/35V ones as the original ones are at 15V "too close" to 25V considering their age.. (..and showing in one of his 34401A repair videos one of the tantalum bricks smoking nicely)..
Cyclotron:
I have repaired two of my acquired 34401a meters by replacing CAPs. They were both from the 1995-1999 range as I recall.  Neither had signs of leaking but I suspected each had a dry cap. Honestly, I'd never seen caps that appeared dry without leakage till I found these two.
chilternview:
I'm a firm believer of 'if it ain't broke, don't fix it'.

34401A's hold their cal and last for years without any special attention, as long as they are not fiddled with. Replacing caps just because something is old is like saying everyone over 60 should have a heart transplant 'just in case'.

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