Re: HP 8643A IO board fault
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On Sun, Oct 28, 2018 at 13:51 Sigur?ur ?sgeirsson < siggi@...> wrote:
Ok, that is good. I find them to be very useful for these
kinds of problems. Also, you might try unplugging modules as you monitor the
current. Something is dragging it down.
Maybe not - I don't find anything getting hot. However, the -15V rail is MIA from the near end of R41, which has gone open. Dead short to ground on the -15V rail, I guess that's my problem :). It's going to be those axial tantalum caps C46/C47 I bet. All the analog MUXes use the -15 rail, so if it's out that'd throw the diagnostics for a real spin.
It was C29, a .22uF 35V SMD tantalum capacitor. All better now, though I need to order a suitable replacement.
So I guess nothing too unusual here. The original fault was a shorted tantalum in one of the RF modules. After that I needed to recap the PSU, then back to a tantalum...
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