Ok, next try unplugging the readout board power connector. P-2171 is the
power. If that doesn't help, then try the output board power
connector.P-1066.
?
You might also plug in a good pair of modules just to give it some
additional load.
?
Per the schematic, there are four unused pins on the protection
board.
?
?
Tom
?
?
?
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----- Original Message -----
Sent: Tuesday, May 22, 2012 10:20
PM
Subject: [TekScopes] Re: Help with R7903
needed to diagnose PS protection problem
?
Hi Tom-
Thanks for the suggestion. I did as you suggested and lifted
one side of R1603 (it's 2.2K), but with the same result. Of course the neon
bulbs don't light since they are on the HV circuits, but I can see the fan
still pulsing. So if I understand you correctly this eliminates that part of
the circuit as the culprit.
I thought I might mention this, though it
may be completely irrelevant: in looking around the scope, I see that the A22
Readout Protection Board, which is a small board connected to A21 Readout
Circuit Board and has a load of diodes on it, has the bottom four pins
unconnected to anything. Can anyone say if that's
normal?
Keith
--- In TekScopes@..., "Tom
Miller" wrote:
>
> Hi Keith,
>
> You might try lifting one end of R-1603 on the high voltage board
A-18 and seeing if the power supply will come up. Note the value of the
resistor as it is a selected part. This would isolate a shorted HV multiplier.
The schematic says it is a X14 multiplier which is the highest I have seen in
a Tek scope. There would be many diodes and caps in that device and any one
can take it out.
>
> I do not have a 7903 to open up and look at
to see how much is involved with accessing the HV section.
>
>
> Tom
