Re: 475a no trace

 

On Mon, 24 Apr 2017 20:30:40 +0000, you wrote:

was using my scope the other day and it just quit showing a trace, so i cracked it open and started looking around, and found the -8vdc rail to be in the mv range.

so i start out at U1464A and see that pin3 is in mv range so i look at R1464 and see on the far side its 50v but the closer side is in mv range, so i check it in circuit and don't really get a good resistance reading, so i yank it out and its bang on at 50K, so i put it back in and low and behold i have trace back, turn it off for dinner, and come back and turn it on and its back to no trace.

rechecking things after shutting off then turning back on i see that R1464 far side is still the 50v as it should be, but now on the closer side of that resistor is 6v.

so what could be the issue? a capacitor? or?
6 volts on pin 3 just means that the feedback divider is working and
the output is 0 volts.

So the output is stuck at 0 volts either because the output of the
regulator is not working or because there is a short on the output.

Measure the voltage across R1468 to find the output current. If the
output current is high, probably about 1/2 amp, then there is a short
on the output which is a common problem; look for a shorted solid
tantalum capacitor.

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