Tweet
I'm working on a friend's 2003 Marshall TSL 100, which he just bought off of Ebay (doh!) and which was DOA. It has a revision 6 mainboard and seems to have stable bias, no NTC issues. Turned out the infamous C46 had vaporized, the 16-ohm switching jack was nicely toasted, and the OT had a shorted primary. I've fixed all of that (new OT, 3kV cap, bypassed jack) and the amp plays nicely now,
EXCEPT
sometimes it won't switch back to the clean channel. Switching AWAY from the clean channel, or between either drive channel, works fine. Switching from either drive channel BACK to the clean channel occasionally doesn't work. The green LED will flicker momentarily and then go out, and there will be no sound from the amp. Switch back to one of the drive channels, and it's fine. It doesn't happen all the time, often with some back-and-forth I can get the clean channel to work, and it sounds fine except for a tiny little crackle at first.
The fact that the sound and the green LED seemed to come and go together, and that the problem comes and goes, made me think that relay RL1 might be the culprit. Could bad contacts in that relay be responsible for this? The green LED and the opto-isolators that control the clean channel are in series with each other and controlled by one side of that DPDT relay. I can hear the click when switching, even when the clean channel doesn't come on... but it could be other relays making the sound.
Seems too simple, and I haven't encountered this issue before on one of these amps. I don't want to make this guy wait a week for a replacement relay from Mouser, only to find out that's not the issue and have to start over. Is there anything I'm missing here? Other common problems that could be responsible?
EXCEPT
sometimes it won't switch back to the clean channel. Switching AWAY from the clean channel, or between either drive channel, works fine. Switching from either drive channel BACK to the clean channel occasionally doesn't work. The green LED will flicker momentarily and then go out, and there will be no sound from the amp. Switch back to one of the drive channels, and it's fine. It doesn't happen all the time, often with some back-and-forth I can get the clean channel to work, and it sounds fine except for a tiny little crackle at first.
The fact that the sound and the green LED seemed to come and go together, and that the problem comes and goes, made me think that relay RL1 might be the culprit. Could bad contacts in that relay be responsible for this? The green LED and the opto-isolators that control the clean channel are in series with each other and controlled by one side of that DPDT relay. I can hear the click when switching, even when the clean channel doesn't come on... but it could be other relays making the sound.
Seems too simple, and I haven't encountered this issue before on one of these amps. I don't want to make this guy wait a week for a replacement relay from Mouser, only to find out that's not the issue and have to start over. Is there anything I'm missing here? Other common problems that could be responsible?
Comment