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Test Equipment Anonymous (TEA) group therapy thread

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Wow, thats so spooky Robert, your trip adds up to to 140 miles, which I take it will be double that for the return journey, and my trip is going to be 145 miles each way unless I also combine it with a trip to RAF Conningsby for some Typhoon action and possible some BBMF action as well as they practise for the forth coming display season, in which case I'll be doing around 330 miles altogether. :-+

Good luck with the HP 8920A and I hope that the surgery is a success for your dog.

Road trip complete. Dog has several fewer teeth and bank balance proportionally fewer pounds  :(

8920A picked up. Looks good. Cal seals are intact so hasn't been robbed or messed with. It also has the high stability reference (050) and Spectrum Analyser / Tracking Generator (102) options.  :)

Less useful is 007 low power input (4W max) but not a huge problem an external attenuator sorts that. I may actually have the high power option in my stock of bits.
Next is extraction of the PSU and see what the damage is. Report is it was working OK and then went "pop" and emitted smoke.


So an hours dissasembly later... Did I say these things are a pain to work on? The failure mode is obvious. We have a blown RIFA 47nF. Unfortunatly this is not in a filter circuit it's a snubbber. The failure start a chain reaction so we have a blown main switch transistor. Literally bits blown off the encapsulation. Blown driver and two smoked resistors.
Now for some parts identification....


m k:
For the backplane,
I've many times wondered how speed and frequency vs. backplane style is sort of misguiding.
Like when bus terminators are needed and wires are carefully placed on PCB and then the wire wrapped backplane is sort of what ever.

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...



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