JCM 600 FX LOOP

Richard Neill

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Hi, I'm wondering if anyone can point me in the right direction with this amp. I genuinely love this amp, however it's had an issue since purchasing it second hand and clearly had a lot of repairs/bodges through its life. Originally it would pop fuses so I changed the valves and set the bias and all was working apart from the serial FX loop. I opened it back up and removed all the connections and then used the schematic to put them back. I noticed that the serial loop was now working but the parallel loop wasn't so I assume one of the connections was the wrong way round originally.

I would love to get the parallel fx loop working again (even though I don't use it very often) but not sure where to look and what to change first. I've replaced the sockets for both the serial and parallel loop with no change (serial loop works, parallel doesn't). Is there any caps, resistors or diodes I should be looking to test or change and if so which ones? Is anyone familiar with the schematics and can point me to the area I should be looking at to resolve this issue? Thanks in advance.

Kind regards,

Rick.
 

Richard Neill

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It really is a special and underrated amp Mark. I can see why people get fed up with it, though, does have some reliability issues. Still this amp will be staying with me for life.
 

Richard Neill

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Found the schematic, changed a couple of resistors but still no dice.
 

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  • JCM600 PSU PCB SCHEMATIC.pdf
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