Marshall VS265 Speaker Issue

[Valvestate]

Hi,

I have a Marshall VS265 guitar amp which seems to work really well on the whole. Clean channel is great, boost 1 and 2 work fine etc.

I noticed recently that it stated sounding a bit "off". This amp has 2 12 inch speakers so I unplugged one at a time and noticed that one speaker sounded great and the other sounded kind of distorted the whole time (but at the same level of volume as the other).

My first thought was that the speaker had blown or something so I plugged the speaker leads from that bad speaker into the "good" speaker. Unfortunately the problem did not go away so it's obviously an AMP issue...

I tried headphones and it seems as though the problem exists there as well.

I would be really appreciative if anyone could point me in the right direction here. I have had amps like this apart before to do minor maintenance so I don't mind cracking it upon - I'm just not sure where to start looking...

Thanks!

[J M Fahey]

Hi.
Being a "two"65 seems to imply it's a 2x65W amp, probably a Srereo Chorus type.
If that's so, it has two separate 65 power amps there, apparently one of them is misbehaving, bu "unfortunately" still working.
You should be able to scope its output, or it will be quite difficult to solve it otherwise.
Sorry.

[Valvestate]

Guys,

Yes it is a 2 x 65W Chorus amp. I don't have a scope so I decided to crack the amp open this evening and see if there were any visual issues. Luckily for me I detected the problem within a few seconds of opening it.

This amp has a motherboard with the preamp stage and tube etc. The power transistors and heat sinks all seem to sit on a separate "daughter" board or whatever you would call it.

Next to the power transistors there are about six large rectangular white 7W resistors. One of these was so loose it was flopping about in the board! I imagined this was the issue to I removed the daughter board and re-soldered all of the large resistors and gave the rest of the underside of that board a visual once over.

I put it all back together and now it's fully functional again!! I guess I got lucky on this one! An easy fix that took 30 minutes to deal with. I'm pleased it wasn't something more serious as my diagnostic skills are limited to say the least.

Thanks for your input and support!