I was given this amp with the story of they had recapped it but apparently put C334 in the wrong way, replaced it then they tried it with full mains power after and nothing went pop, I put it on the bulb first as no idea if that was all true.
Any how where to test / troubleshoot first? Apart from confirm psu voltages? I'll attach schematics.
Attachments
I would expect C334 would just explode if fitted incorrectly. Ultimately it is only a small rail decoupler and the power supply should have blown it out of existence and a normally working amp carry on as normal.
An unknown history is never good when something has been worked on by persons unknown in the past.
We have to go back to post #1 and the the bulb being bright even with the amps disconnected. If you are certain the -/+ 52 volt rails are isolated from the output stage then there is really only the bridge rectifier and the reservoir caps.
I can't see any issue with the -/+55v regs and their output loading the supply that much (because I would have thought the 10 ohm 1watt fusibles would fail) but I suppose it is worth at least looking. Removing the fusibles isolates the regs.
An unknown history is never good when something has been worked on by persons unknown in the past.
We have to go back to post #1 and the the bulb being bright even with the amps disconnected. If you are certain the -/+ 52 volt rails are isolated from the output stage then there is really only the bridge rectifier and the reservoir caps.
I can't see any issue with the -/+55v regs and their output loading the supply that much (because I would have thought the 10 ohm 1watt fusibles would fail) but I suppose it is worth at least looking. Removing the fusibles isolates the regs.
That all sounds promising.
Next check would be the output voltage from the -/+55 volt regulators. Note this output voltage is higher than the main rails. The input side to the regulators consist of a 'voltage doubler' and so you could see -/+100 volts or more on the 330 ohm fusibles.
If all that checks out then the power supply would seem to be OK.
Next check would be the output voltage from the -/+55 volt regulators. Note this output voltage is higher than the main rails. The input side to the regulators consist of a 'voltage doubler' and so you could see -/+100 volts or more on the 330 ohm fusibles.
If all that checks out then the power supply would seem to be OK.
That all sounds good.
If you disable the bias generator on both channels and provided there are no obvious shorts then the amp should power up when its all reconnected. Each channel will happily work for testing with just a single pair of output transistors fitted. It would also be fine for being driven to pretty high levels with just one pair.
Lifting this resistor disables the bias generator.
If the bulb lights brightly you most likely have a fault and that would have to be looked at under bulb conditions.
If you disable the bias generator on both channels and provided there are no obvious shorts then the amp should power up when its all reconnected. Each channel will happily work for testing with just a single pair of output transistors fitted. It would also be fine for being driven to pretty high levels with just one pair.
Lifting this resistor disables the bias generator.
If the bulb lights brightly you most likely have a fault and that would have to be looked at under bulb conditions.