I haven't looked for the actual cause of failure yet, but it's likely that there is one since resistors rarely 'just fail' unless overloaded (though very rarely, they do, and if one went the other would quickly follow), and it could be anywhere from the rectifier IC onwards.Īre the fans running on your one? They aren't on this one, they're driven from that part of the supply. This is clearly an intended/expected failure since there's an instruction printed on the board that the resistors must be spaced at least 10mm from it. The initial problem is that two 2.2-ohm resistors (R202 and R223, at the end of the rear board), which appear to be 'pseudo fuses' on the lower-voltage rectifier, have gone open circuit. Interesting - the internal fuse is OK (and there is only one).
![marshall avt 50h 2000 marshall avt 50h 2000](https://www.libble.eu/bestanden1/60077/bg1.png)
You're not in Glasgow by any chance are you Matt? and I wasn't convinced, with the standard module.Ĭlick to expand.By an odd coincidence, one of the jobs waiting for me at the shop today is an AVT150 with exactly this fault! The second amp belonged to the shop - bought in very cheap, dead - so I wanted to make sure it could be properly warrantied for resale. and it's bad for my reputation if I fix something and it breaks again.)
#MARSHALL AVT 50H 2000 FOR FREE#
(Marshall were good enough to send a replacement module for free the last time this happened, but I still have to do the labor again. which is the important part as I was already eating the cost of the repair after I fixed it the first time. It didn't cost as much for the kit or take as long to build and fit it as you might think - around four times what using the standard Marshall replacement module would have done on both counts, if you include testing (which I would do even if using the 'official' part) - but I'm pretty sure after that sort of test that it's never going to fail again. The time and trouble wasn't for the amp, it was for me.
#MARSHALL AVT 50H 2000 FULL#
I tested the rebuilds by cranking them at absolutely full volume (way above what anyone would run the combo at, I hope!) into a Powerbrake for an hour, continuously, during which the Powerbrake's fan went about as fast as the amp's - but the MG100 chassis got only mildly warm, even right under the power transistors. I did leave the fans in the amps as well - though obviously not now blowing directly on the power module, which is heatsinked by the chassis - it seemed pointless to take them out or leave them not doing anything, although they do make a fair noise. Good design should not require emergency measures like this on a simple low-powered (which 100W is, nowadays) audio output stage, IMO. It's incredibly borderline component spec'ing. "which is why all the AVT power amps, from the AVT50X upwards, are fan cooled for optimum reliability."Īctually they're fan cooled - really 'forced' cooling too, we're not talking about a fan gently blowing air around the amp - because if they aren't, the chip has a life expectancy in minutes at most.
#MARSHALL AVT 50H 2000 SERIES#
Unfortunately the AVT series are a bit more complicated inside and I don't think there would be room to do the same thing.Īnd yes, they are serious that the little black thing in the first pic is the entire output section for a 100W amp. I did the second one as well once I'd found out how well the first one turned out.) (The really sharp eyes will spot that those are actually two different amps. It not only stopped the thing blowing up, it sounds way better than stock too.
![marshall avt 50h 2000 marshall avt 50h 2000](https://media.musiciansfriend.com/is/image/MMGS7/Valvestate-2000-AVT-50H-Guitar-Amp-Head/000000117103228-00-500x500.jpg)
I purposely used the rectifier diodes and filter caps that come with the kit as well, even though that's duplicating the ones on the main board - I thought it might be an idea to add more, and separate from the preamp. It fits perfectly in the space in the chassis - six holes to drill, and it hooks up to the main circuit using the same points as the old module did (you just have to identify which of the multiple wires do what). That's a Velleman/Maplin (UK electronics chainstore) 100W power module kit. Just a little experiment after the same amp blew its module twice and I really didn't want to just keep throwing modules at it, even at the tiny amount of money they cost (annoying for the customer, too).