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2022-01-22, 15:27:29
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Author Topic: Can anyone help GRUMAGE fix his scope PLEASE  (Read 28513 times)
Group: Elite
Hero Member

Posts: 3539
It's turtles all the way down
Dear ION.

Yes the squeal continues until I press the power off button.

Cheers Grum.

This tells me either:

1) the scenario I outlined earlier is correct or

2) the squeal occurs because the optoisolator is not pre-emptively shortening the ramp cycle because one of the secondary supplies is not available. If the secondary voltage collapses for some reason (shorting part) the opto isolator will turn off, allowing the ramp to run to the end until SCS trips from overcurrent in the CSR resistors.

The function of the optoisolator H1045 is to shorten the ramp by turning on the SCSS before it reaches fault trip current on each cycle, thus regulating the supply since it is driven by sensing two of the voltages, the +10 and the -12 as reference. If it is not pre-emptively shortened, the inductor has not enough time to dump its remanance magnetism, therefore it saturates causing the squeal.

This does not necessarily mean the opto is bad, it could be any of the parts in the feedback loop or non of the feedback parts since you stated earlier that the squeal starts when the secondary +/- 12 collapses. The feedback loop may actually be trying to do its job by allowing extension of ramp time until it senses the target voltage is acquired. In this case, target votage is never achieved so it runs on to the end of the ramp, then trips out on over current, then starts another cycle.

Understanding how this part of the circuit works is crucial and will lead you to the goal.

Check the voltage on C1012, it should be around +15 volts per the schematic or the ramp shortening via the opto will not occur.

Then test all of the power supply secondary voltages to see which of those collapse completely and which try to survive.

"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

Group: Moderator
Hero Member

Posts: 2449

Buy me a cigar
Dear ION.

Thank you for taking the time, it is really appreciated.

It is late now so will take a look at the points you have raised tomorrow.

Again thanks, Cheers Grum.

Nanny state ? Left at the gate !! :)
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