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I've got a Randall RG50TC stuck in the clean channel. While playing, it switched on its own from overdrive to clean. However, the overdrive and clean channel LEDs were lit simultaneously.
When I attempt to put the amp in the overdrive channel (footswitch or switch on the control panel), the gain 1/2 LEDs of the overdrive channel(s) do not illuminate, both clean and overdrive channel LEDs are illuminated (only clean LED is illuminated in clean channel). Clean channel seems to work fine.
Capacitors C27, 28, and 30 are fine but the three capacitors adjacent to those three (can't see the numbers, C29 seems likely to be one of them) are blown (tops are convex). C27, 28, and 30 appear to be the same cap specs. I'm fairly sure the caps are unrelated.
Reverb seems not to be working (though Reverb LED/switching works fine so this also seems unrelated - I have not had a good look at the circuit diagram to trace this out). Wish I'd tried it before disassembly to try to resolve the channel issue (see below regarding disconnecting internal connection for the footswitch). Can't be sure if I did that or if it is related. I hadn't used this amp in a very long time, can't say I know reverb was working before channel issue...
Disconnected the internal wiring harness (inside the amp) for the channel switch on the footpedal. Stays in clean channel, no LED or other noticeable changes when front panel switch is toggled. Looking at the schematic it would seem to me disconnecting this harness should have had no effect. However, connectors do not appear to be shown in the circuit diagram so it is hard to say what effect this had exactly.
Reconnected footswitch internal harness and previous symptoms reappear. Noted that clean channel LED dims (hardly noticeable) when I try to switch channels and there is a slight buzzing noise.
Q4 seems like a logical point to start at. Not sure how best to check it though (I'm a mechanical engineer who has taken an extra electronics course or two not too far in the past...). This area of the circuit (mid height left side of the linked schematic - rotated such that the text is upright) seems sure to be my area of interest.
Diagram is here:
http://www.echostar.pl/~zelman/RG50TCSchemat.pdf
Any advice would be very much appreciated.
When I attempt to put the amp in the overdrive channel (footswitch or switch on the control panel), the gain 1/2 LEDs of the overdrive channel(s) do not illuminate, both clean and overdrive channel LEDs are illuminated (only clean LED is illuminated in clean channel). Clean channel seems to work fine.
Capacitors C27, 28, and 30 are fine but the three capacitors adjacent to those three (can't see the numbers, C29 seems likely to be one of them) are blown (tops are convex). C27, 28, and 30 appear to be the same cap specs. I'm fairly sure the caps are unrelated.
Reverb seems not to be working (though Reverb LED/switching works fine so this also seems unrelated - I have not had a good look at the circuit diagram to trace this out). Wish I'd tried it before disassembly to try to resolve the channel issue (see below regarding disconnecting internal connection for the footswitch). Can't be sure if I did that or if it is related. I hadn't used this amp in a very long time, can't say I know reverb was working before channel issue...
Disconnected the internal wiring harness (inside the amp) for the channel switch on the footpedal. Stays in clean channel, no LED or other noticeable changes when front panel switch is toggled. Looking at the schematic it would seem to me disconnecting this harness should have had no effect. However, connectors do not appear to be shown in the circuit diagram so it is hard to say what effect this had exactly.
Reconnected footswitch internal harness and previous symptoms reappear. Noted that clean channel LED dims (hardly noticeable) when I try to switch channels and there is a slight buzzing noise.
Q4 seems like a logical point to start at. Not sure how best to check it though (I'm a mechanical engineer who has taken an extra electronics course or two not too far in the past...). This area of the circuit (mid height left side of the linked schematic - rotated such that the text is upright) seems sure to be my area of interest.
Diagram is here:
http://www.echostar.pl/~zelman/RG50TCSchemat.pdf
Any advice would be very much appreciated.