No Signal, no presence or depth lights, post repair - what's the damage

Power Amps LXII
1

Hi All,
I just got back from a tour where my LXII may have been exposed to bad power. Plugged in one day and got no signal out. Presence and Depth switches would not illuminate. No external fuses appeared blown. Took it Torrence Electronics (amazing place) the following day to see if we could get it working before than evening’s show. Spoiler: we did. They opened it up and tested through component by component, and couldn’t find any bad internal fuses, or anything that tested badly. However, one of the connectors from the input power transformer was scorched, so they tested the power tubes for shorts. There were none. All power tubes were fully operational, though they tested as being close to the end of their useful lives. I replaced the power tubes, and we hooked everything back up, and it then it just worked. We finished the tour without incident. Played another show back back home. When I plugged it in after that, same issue. Haven’t opened it up yet, so couldn’t tell you about the state of the almost new power tubes. Anyone had anything like this happen before? Can the amp be saved? My backup doesn’t bring the thunder the same way.

Thanks

2

Welcome to the forum!

The culprit is that connector from the power transformer to the tube PCB. The two conductor one with green leads. You described that as burnt looking, which would indicate that the contacts were oxidized, causing high resistance, leading to excess heat followed by connection failure.

I recommend clipping off the connector and soldering the leads directly to the PCB. Takes 10 minutes.

Later units have a connector with better, more oxidation resistant pins.

Dave

3

Thanks Dave! Is there any risk of creating further damage down the line if whatever caused the oxidation happens again with the soldered connection?

4

No, The soldered connection won’t give you issues as long as the connector is carefully removed first.

The connector shouldn’t have had that issue either. Unfortunately the contact plating on the earlier part didn’t hold up very well. That got replaced with a more oxidation resistant part.

Dave