Aphex 207 issues

Hey guys. Long time lurker here, and first post!

I just copped one of these Aphex with the usual issue: the unit takes input signal, shows in both meters, but, the "power" light stays yellow and never turns to green. So I get signal but absolutely no output.

Aphex says there is a warm-up delay for the tube but in this case, it's perpetual. Any idea how this circuit works?

On the PSU I found:
U1 is a PWM chip UC3945
U2 optocoupler chip CNY17F-2
D8 diode that has been resoldered on a trace

There's also an array of transistors 2N3986 that have also been resoldered.

Any input would be appreciated! Or a schematic, of course.

Thanks to anybody that can shed some light on this!

It's a 2-channel unit. Are both channels the same or is the indicator for both?

If the indicator is for both channels then it's likely a power supply fault as the PSU will be common to both

Check the various voltage rails to see what's not working. Aphex may well have provided test points for this. There is likely ± 15 V plus whatever voltage is used for the valve section. If there's any logic in it there will be a +5 V rail as well

If you're seeing meters moving with signal you'll probably find that the ± 15 is working but one of the other rails isn't

Nick Froome

Check solder joints on the cables that connect the boards, this solved some issues on one I serviced.