LP125sa - plate fuse blown.. now what?

[AlexM]

Hi All,

I recently replaced the output tubes in my LP125sa, and after about three days of successful running, I have found that I have no output on the left channel, and the plate fuse indicator is illuminated.

The instructions on how to replace the fuse are somewhat opaque in the manual, although all becomes clear when you remove the base cover.

Sure enough, the left channel plate fuse is open circuit. Is it ok just to replace it and hope for the best?. I am presuming that there must have been some fault on one of the replacement tubes to cause it to blow. Am I running the risk of a problem by replacing it to test the tubes?

Regards,
Alex

[edkoz]

If it was me, I would remove the new tubes from the channel that blew and replace them with the old tubes to begin with. If the fuze blows again I would disconnect all IC/speaker wires and try again

[AlexM]

Thanks - that sounds like a sensible plan.

I hve had a look at the circuit board, and it looks like there is a lot of flux around the base of the of the sockets, and what looks like some possible scortching on the board. I'm going to examine it more closely tomorrow, and if I don't like the look of it it will be going back to the dealer for inspection and a check-over before I run it again.

I do hope there isn't an issue as I would be unlikely to get it back this side of Christmas

Regards,
Alex

[John49]

Originally Posted by AlexM

Thanks - that sounds like a sensible plan. I hve had a look at the circuit board, and it looks like there is a lot of flux around the base of the of the sockets, and what looks like some possible scortching on the board. I'm going to examine it more closely tomorrow, and if I don't like the look of it it will be going back to the dealer for inspection and a check-over before I run it again. I do hope there isn't an issue as I would be unlikely to get it back this side of Christmas Regards, Alex

AlexM... Hope you get it fixed before Christmas. Not much ho-ho-ho if you have no music to listen to... Happened to me one year. Had a dreadful time, reduced to using a portable Radio / CD player.

[AudioGremlin]

Remember that generally tube power amplifiers require that the speakers are already connected on power up. It may not be a good idea to disconnect everything.

[AlexM]

OK, so I've had a closer look, and it isn't good news. there is a blown track around the base of v10, so the amp is a non-runner. I am engaging with the distributor about a return for repair, but it isn't going to be pretty - will need a hard-wired repair to the board, which I'm conceptually unhappy with.

[Briz Vegaas]

Bummer. Sorry to hear about your amp woes. I just replaced the KT120 s in my LP70s. Maybe i should keep my fingers crossed. Its been very settled now for a while ( touch wood). Glad i didn't upset the apple cart, so to speak. I have only one suggestion for you. Mono Beatles. Have a very 60 s retro Christmas.

PS oh, sorry, you have the stereo version, not the monos. I was think SE not SA.

Bummer.

[AlexM]

Hi Briz,

That's ok - I still had one working channel so the Beatles in glorious mono was still an option .

Actually, thanks to the highly responsive distributor the amp has been repaired already and will be back with me imminently. Cause was an undisclosed manufacturing issue and was repaired FOC - can't say fairer than that, I suppose.

Cheers,
Alex

[AlexM]

Amp is back from repair and installed in the system, and sounding very nice indeed.

The damaged track has been repaired, presumably with a patch wire. It wasn't a tube related problem, but an issue with the solder mask being damaged that allowed a flash over, which is what caused the track to burn before the plate fuse blew. Not very happy with that, but it was fixed under warranty so no complaints about the service support.