Products > Test Equipment
Test Equipment Anonymous (TEA) group therapy thread
tautech:
--- Quote from: Robert763 on June 02, 2023, 07:39:09 pm ---Anyway, one of the primary windings was open circuit.
--- End quote ---
Had the glue corroded the winding ?
factory:
--- 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
Robert763:
--- Quote from: tautech on June 02, 2023, 07:48:26 pm ---
--- Quote from: Robert763 on June 02, 2023, 07:39:09 pm ---Anyway, one of the primary windings was open circuit.
--- End quote ---
Had the glue corroded the winding ?
--- End quote ---
No. When the MOSFET when short due to the snubber failure the main (300V DC) filter capacitor discharge path included the winding and it fused.
Robert763:
--- 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.
[ Specified attachment is not available ]
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
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