Electronics > Repair
HP 54502A repair once again
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vanhouten:

--- Quote from: wn1fju on October 25, 2014, 11:00:56 pm ---On my Boschert supply, I replaced ALL the electrolytics, the switching transformer, the opto-isolator, pulled and checked all the flyback diodes, checked all the FET/BJT regulators they put in the back end, and on and on.
I got close at one point, but never completely fixed it.  I keep it around in plain view to keep me humble.

--- End quote ---

This sounds like a lot of fun... that I am probably going to miss.
Maybe my Boschert will get framed an have its place on the wall of shame as well  ::)
Just went through the spec-sheets of the Meanwell PSUs and they read like the most reasonable solution to me.
The service manual of the 54502A does not mention the 3.5V-rail to be of any particular use either.
I think I am going to order a new fan as well while I am at it.
Thanks again!
Shock:
Some photos of the board would be nice.
Smith:
As for accetable PSU noise:
Set the scope on the most sensitive level and watch the noise level. You might check the calibration outputs for noise too. I guess noise figures should be noted on the service / calibration manual. If those are not exceed it shouldn't be any problem.

As for the repair, yes repairing this PSU is a pain in the @$$.  Most repairs I heared about failed and ended up with buying a replacement. Thankfully I have access to lots of professional tools, doing this at home would have been a nightmare.
vanhouten:

--- Quote from: Shock on October 26, 2014, 02:00:29 am ---Some photos of the board would be nice.

--- End quote ---
Indeed, sorry for the shortcoming but my lab-camera is somewhat outdated.
There has been a well documented tear-down of the 54502a in this post including the PSU.
https://www.eevblog.com/forum/reviews/hp-54502a-nearly-vintage-digitizing-scope/
wn1fju:
As described earlier, here's a picture of my replacement power supply for my HP 53310A.  The general layout of the unit (main board, CRT board, CRT, etc.) should be close to the HP 545xx series.  The only part I re-used from the original Boschert supply was the female connector from the AC filter.  I couldn't find a suitable replacement for the output connector so I just tacked extra wires on the cable going down to the main board (after snipping off the male connector).

My only concern is whether or not all the nice wiring acts like antennas and transmits the switching noise.  I suspect it does a little and I suppose I should try to cover the entire supply with some more sheet metal.
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