Electronics 2000

Hi there, Only just registered here please be gentle.

I've started repairing guitar related electronics as a bit of a side hobby. I used to work on large valve radio TX/RX's when I was in the TA back in the 80's (yes the army was still using valves then) and I've been asked to repair what appears to be a mono power amplifier manufactured by Cloud / Johnson Soundaround. The model number on the main board is JSA 5003.

I've contacted Cloud via email but I have a feeling they may not be helpful in releasing schematics.

It looks like the internal (HT??) F4A fuses have both blown which is consistent with the last know behaviour of the device. But I'd like a schematic so I can do a thorough check.

Does anyone have any experience of this equipment?

Google is probably your best starting point for schematics.

Are the fuses in the mains supply, or the HT supply? Check any capacitor that is connected directly across the mains, and electrolytic smoothing capacitors. If the fuses are in the HT supply, check for shorts in the smoothing caps. These capacitors are in highly stressed positions, and all too often do not have a substantial enough safety margin (often the case in consumer electronic equipment). Btw, if the fault is on the HT line, the rectifier diodes/tube will probably need replacement as well.