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Originally Posted by Tim Farrant The circuit driving the leds might have lost it's power supply bypassing and is oscillating when switching the leds. This might be a LM339 quad comparator chip singing away to itself. Have you got any schematics for this unit? |
Thanks for the reply Tim. Found a schematic on the Symetrix website, bless 'em. There's a LM339 running the 5 gain reduction LEDs, but these don't seem to be noisy.
The chip driving the three threshold LEDs is a 4560 (not socketed), pins 2 and 6 grounding through C20 (.056 mylar). Might replacing C20 be a good (and easy) place to start?
Pots have cleaned up nicely, Cailube to the rescue...
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Have you got a scope you can hang onto the led legs and take a look?
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No, afraid not.
John Pitcairn