20210915_134426
PelliX

20210915_134426

Intermittent loop bypass switch?... with nothing in the loop, i assume you'd only hear the relays....
 
Yes, sort of. What was happening (and, doesn't happen anymore however much I try) was that RL1 was flipping into the 'energized' position which switches the Return on. Because it was only doing so for a split second, the signal (entering the front of the amp) wasn't actually dying in time for it to become very apparent.
I've checked
  • the switch itself, seems absolutely fine.
  • the resistors involved. In circuit, but the voltage drop and measured resistances remain stable.
  • the smaller electrolytic caps in the middle of the board and to the right around IC2 (TL072CP buffer). All dead on spec.
  • the solder joints for all components involved by optical inspection, chopsticking and even lightly bending the board.
  • the voltages on the relays in rest and energized states - stable and fine, certainly didn't witness any current leaking in while the FX loop is set to off.
  • the cable/wires between the mainboard (CN18) and the board for the FX loop, switch and DI out. No fault found.
  • the flyback diodes (D13, D14) for the relays - same forward voltage, both measure correctly.
  • the voltages on the secondaries of the PT. I'm not sure what they should be as I'm lacking a datasheet for the transformer and the heaters seem a bit high, but stable.
I'm at a loss right now, honestly. When/if the problem rears its head again, I'll see what I can do... :shrug:
 
... ah... so that's where my comment went...I ment to comment on the thread, then couldn't see it and went on with other things... hope you get it sorted..
 

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JCM800 SC20h
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