Switch mode PA Amp PSU fault

[Yorkie]

Thanks for the info Nick. I think the dry joint on the PCB has cased arcing between the track and the lead-out wire of the cap. The cap itself isn't swollen and has no physical signs of any problems, but over time, (five years), as is all too common, it has developed a high ESR, which I think SMPSUs are particularly intolerant to. In another thread I mentioned that I had a TV antenna amp which had developed a fault. It had a simple conventional PSU and a separate amp unit in the one case. The electrolytic cap on the PSU had a high ESR and when I fitted a new one, the amp was fine and is now back in use.

I'll report progress, and I hope it will be good news, but I'm not going to spend too much time on this - the amp is still in production, so I'm assuming that a replacement PSU will be available.