Greetings !
I have a HP4396A network/spectrum analyzer, and yesterday the power supply failed.
The diagnostics tells me there is a problem in the post-regulator.
The symptoms have included a sour smell for some time and unstable RF level on the display that stabilizes as something warms up.
Now the RF level jumped outside the display area, so I suppose some OP-AMP voltage is wrong.
I have gathered that the power supply is fully undocumented and the post -regulator is quite complex,
with a lot of pins towards the backplane.
But in the best case I could find a physically damaged component and swap it for a working one.
I saw that "mark03" attempted to repair a AGILENT 4396B which seems to have the same/similar post-regulator board.
https://www.eevblog.com/forum/repair/agilent-4396b-spectrumnetworkimpedance-analyzer-repair/To begin with it would be useful to know if the input voltages to the post-regulator are fine.
The measured voltages on the "10 pin rainbow cable" are as follows.
1: -18 VDC
2: +17.8 VDC
3: GND
4: GND
5: +7.6 VDC
6: -7.9 VDC
7: +70.5 VDC
8: +25.6 VDC
9: +2.5VDC, 3VAC
10: GND
So I was wondering if anyone could help me verify if those voltages are fine ?