Trace Elliot - Rescue & Restore (and bargain finds)

[Sparky Mark]

20 minutes ago, Rosie C said:

 

My friend is a knowledgeable amp tech     

 

She explained it to me (though I've since been to Google to make sure I get it right here)...

The 50Hz AC mains is rectified, converting it into a series of positive DC pulses, and the capacitors smooth the pulses into a steady DC voltage. If the capacitor isn't working properly, the ripples aren't fully smoothed and you can hear a ripple frequency in the speakers. But because it's between the peaks of the rectifier wave the frequency has been doubled to 100Hz.

 

I found this drawing which sort of shows the frequency doubling...

 

That's good information; no disrespect intended towards your friend. I recently replaced some swollen but still working capacitors in a 1980s NAD amplifier because I could see they were damaged. The good news is that new capacitor technology has moved on and you should be able to find replacements in smaller packages.

[Rosie C]

1 minute ago, Sparky Mark said:

That's good information; no disrespect intended towards your friend. I recently replaced some swollen but still working capacitors in a 1980s NAD amplifier because I could see they were damaged. The good news is that new capacitor technology has moved on and you should be able to find replacements in smaller packages.

 

 

None taken!

 

Nice work! I did look on ebay earlier for new capacitors, but immediately realised that I don't know what sort of pins they have soldered to the PCB - some of the new ones have wires, while some of the larger values have flat blades - so I can't progress until we open the amp again and this time look at the underside of the PCB.  

[Sparky Mark]

3 hours ago, Rosie C said:

 

None taken!

 

Nice work! I did look on ebay earlier for new capacitors, but immediately realised that I don't know what sort of pins they have soldered to the PCB - some of the new ones have wires, while some of the larger values have flat blades - so I can't progress until we open the amp again and this time look at the underside of the PCB.  

Cheers. Hopefully you won’t need to do too much disassembly to get to the underside of the PCB. Old solder joints and connectors can be rather fragile and crack when disturbed, causing more issues. Desoldering large caps can also be a bit of a PITA, due to needing a fair amount of energy from the soldering iron to melt the solder sufficiently to remove without lifting the PCB track/pad.

You are very lucky to have a friend with the knowledge to help fix your amp. 

Edited 13 hours ago by Sparky Mark

[tauzero]

9 hours ago, Rosie C said:

While we had the case open, I took a photo of the power supply capacitors. There's a bit of 100Hz hum on the speakers and we're suspecting dried out capacitors. There's a bit of work to do to remove them though.

 

 

That's either "5 go mad with the heated glue gun" or there was a bukkake party while they were building the amp.

[Rosie C]

7 hours ago, tauzero said:

 

That's either "5 go mad with the heated glue gun" or there was a bukkake party while they were building the amp.

 

I know! For bonus fun there's that little capacitor beside them, just asking to be damaged