Products > Test Equipment
Test Equipment Anonymous (TEA) group therapy thread
factory:
--- Quote from: Robert763 on June 02, 2023, 08:26:06 pm ---
--- Quote from: factory on June 02, 2023, 08:10:13 pm ---
--- Quote from: Robert763 on June 02, 2023, 04:53:03 pm ---HP 8920A Radio test set PSU repair update.
On the mains side we have literally blown up IRF 840 main switch MOSFET, ZXT650 driver bipolar, 0.1R 1W, 4.7R 1/4W resistors and 47nF RIFA. Not obvious is 9.1V 1.3W zener short circuit. Replacing those got it running but output voltages ar a bit off and a couple of output electrolytics getting warm ::)
Most of the output electrolytics were starting to leak physically and electrically. So replaced all those too. Just having a cup of coffee before a final check and putting the PSU back together and plugging in...
Robert.
--- End quote ---
Having read your repair, I'm glad I replaced the RIFA madness snubber cap, in the HP 54615B* scope when I acquired it, seems to also use a Computer Products PSU, but not the same one.
Are you going to name & shame the peeing capacitors?
*Seems Scottrade has a basket case 54615B, described as missing the power socket, nope missing the whole PSU more like. :-BROKE eBay auction: #325678748332
David
--- End quote ---
The Failed parts. Not much left of the ZTX650. he fuse just did it's job.
(Attachment Link)
--- End quote ---
Thanks, will have to take a closer look at the PSU next time I work on it, seems to mostly have Nippon Chemi Con LXF, with some Rubycon, but lots of glue hiding the details.
David
Neomys Sapiens:
It is power supply season, isn't it?
I had another look at the Analogic 2030 sythesizer/function generator and the culprit seems to be the PSU for the analogue board. More on this soon..
Robert763:
--- Quote from: factory on June 02, 2023, 08:40:17 pm ---
--- Quote from: Robert763 on June 02, 2023, 08:26:06 pm ---
--- Quote from: factory on June 02, 2023, 08:10:13 pm ---
--- Quote from: Robert763 on June 02, 2023, 04:53:03 pm ---HP 8920A Radio test set PSU repair update.
On the mains side we have literally blown up IRF 840 main switch MOSFET, ZXT650 driver bipolar, 0.1R 1W, 4.7R 1/4W resistors and 47nF RIFA. Not obvious is 9.1V 1.3W zener short circuit. Replacing those got it running but output voltages ar a bit off and a couple of output electrolytics getting warm ::)
Most of the output electrolytics were starting to leak physically and electrically. So replaced all those too. Just having a cup of coffee before a final check and putting the PSU back together and plugging in...
Robert.
--- End quote ---
Having read your repair, I'm glad I replaced the RIFA madness snubber cap, in the HP 54615B* scope when I acquired it, seems to also use a Computer Products PSU, but not the same one.
Are you going to name & shame the peeing capacitors?
*Seems Scottrade has a basket case 54615B, described as missing the power socket, nope missing the whole PSU more like. :-BROKE eBay auction: #325678748332
David
--- End quote ---
The Failed parts. Not much left of the ZTX650. he fuse just did it's job.
(Attachment Link)
--- End quote ---
Thanks, will have to take a closer look at the PSU next time I work on it, seems to mostly have Nippon Chemi Con LXF, with some Rubycon, but lots of glue hiding the details.
David
--- End quote ---
Well I'm not a fan of "shotgun" capacitor replacement but this one could have caught me out. There was no sign of any issues with them. When removed it was obvious they were leaking. Even worse a couple were starting to burn the PCB. I didn't replace the main high voltage filter capacitors as they checked out fine when removed.
[ Specified attachment is not available ]
The Advance manual arrived yesterday thank you very much. I've not looked at it yet. Been busy. New rule to keep workhop tidier, no starting new projects until the current one is finished or put away in a Really Useful Box.
Robert.
Robert763:
The 8920A is fixed and passes all tests.
£75 and some parts I had in stock :D I claim the Jammy Git.
[ Specified attachment is not available ]
m k:
--- Quote from: factory on June 02, 2023, 08:40:17 pm ---will have to take a closer look at the PSU next time I work on it, seems to mostly have Nippon Chemi Con LXF, with some Rubycon, but lots of glue hiding the details.
--- End quote ---
Glue under big reservoir capacitor also, not snap in then?
At least easier to remove, if that finally is a positive thing.
Is bottom right also glued between mains choke and the bridge?
Is there some other glue inside a heatsink?
Seems that they really tried to put everything possible in for the machine soldering.
Some coils seem to be without any glue, maybe the glue is just hiding.
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