Marshall TSL 100 clean channel muted need help please

[xjbear]

doing some small tweaks to a friends TSL100, new OT, cut some treble, fix footswitch retube and bias. There are some switching mods, remove a few transistors and fets off the board to improve switching time out there, i did those too. when testing the amp i had barely any sound out of the clean channel but some huge pops and clicks and scratchy gain and vol knobs. reversed all the switching mods back to stock and now its just quiet and muted with the occasional quiet pop and scratch noise.

The other channels work perfect, all other features of the amp work and switch normal, all the LEDs light up even the clean channel, the problem persists even jumping the fx loop with patch cable, all the controls on the clean channel have no effect at all, swapped tubes and re tensioned sockets, pulled ALL boards and checked and re flowed solder joints.

There is a pre existing condition of the footswitch acting wierd, 2 stomps of the crunch button one stomp of the clean to switch back to clean, my guess is the relay or relays and maybe they/it took a final dump when i coincidentally had it opened up, I know nothing of opto/transistor switching systems, I do know that this amp mutes while switching and it sounds like the clean channel might be stuck in that muted spot?

Thats all I got if anyone has any experience with something like this please give me some insight
Thanks
Bear

[DrGonz78]

The clean channel gave me all sorts of trouble too... But that is another story that I can't help with any information. I took it to field services and they could not figure some troubles I was having w/ the clean channel. That is not really in relation to your post.

However, that problem w/ the foot switch is something that I had trouble locating the right momentary switch part. Read this >>>
http://music-electronics-forum.com/t28148/

That might help you figure out the problem, since you describe *almost* the same exact symptom that I had after replacing the switch.

[xjbear]

yep I read your whole thread hoping for something to pop up, along with EVERY other TSL100 thread in existence lol to no avail, I know theres some diehard techs on these pages so hopefully someone will chime in, Thx Man! Oh yea, what became of your amp?

[DrGonz78]

I just sold it yesterday!! LOL! It actually was fine until I tried to clean the pots (hence all the Volume and Gain pots) since all of these were scratchy on all three channels. The Crunch and Lead were improved but after putting it back together I had a problem w/ the clean channel. It was not scratchy but actually there was a signal bleed w/ Vol and Gain all the way down on the clean channel. Both the other channel w/ Vol and Gain all the way down cut all signal. I then tried to figure out why this happening and eventually brought it Field Services. The guys there are great too. I returned to pick it up (no charge) and he was like I could spend 2-3 days only looking at this amp to try to figure this out. So it was not financially practical to have them do that.

But as far as SPDT type switches, I got the ones listed on that thread to replace the old broken one(crunch). I had to open up the switch and rotate the flipper. I bet there are more practical ways to go about it but finding a switch that would fit without intruding on the circuit board proved to be difficult.

[xjbear]

so you still had a signal through the clean channel even with gain and volume all the way down....but as you increased volume and gain your signal increased as normal?

thats quite similar to my issue but i dont get a normal volume out of it ever, it stays at a slight signal, same volume always...its interesting because my thoughts were that the signal might be backfeeding through the opto/switching circuit and coming out that way and the normal audio path is being interrupted by a bad relay/whatever on the way back from the main board into the clean circuit.

your amp then even tho the normal audio path was working vol/gain, with those down all the way your getting the same slight signal back/feeding through the circuit
this tells me something just dont know what, its a job to press fit this crap into my brain, i'll go chug some OJ and meditate

funny thing, i was freaking out on how gooood this thing sounded after the mods to the crunch/lead channels but thought i'll never own a rat nest like this, but bought a DSL100 yesterday ha, but it was with a 1960av cab for $950 so couldnt not buy it you know

[xjbear]

update...pulled all relays and tested they are all good

[g1]

You are dealing with 2 separate issues here. You mentioned the footswitch problem was pre-existing. It sounds like either the clean or crunch switch have been replaced with a latching type when it should have been a momentary type. Should be easy to check with your multimeter.
The other problem with the clean channel being quiet now does sound like it is being muted as you mentioned. If it only started after doing the mods, then it seems likely that is the source of the problem. You said you removed the mods but you need to triple check that everything is back to the way it was before the mods.
The muting is usually done by the FET's. Any chance one of them got put back in backwards?

[xjbear]

Ive not even plugged in or repaired the footswitch yet, so all posts are with out the footswitch present in the circuits.

all the fets are in correctly.

I did just check all the optos on the clean channel board as well and they test fine, yhey are normally open circuit, but with 2volts present show resistance, im assuming when lit, they power the transistor which shunt the signal to ground and mutes the channels output?

[xjbear]

1.7vdc to optos in clean mode, 1.2vdc switched out, same voltage is used for the clean channel pilot light, but it goes out yet voltage remains on optos, wierd, this things making me hurt

Also the schem I have off Dr tube shows a connector 15 on the main board, my board only goes to 14, maybe im working off the wrong schematics, this is the newest board JCM-60-00

[xjbear]

Fixed it!!!!!!!!

I guess i lied when I said I put all the mods back to stock, I was following the Europa list of current mods to the TSL 100, it says on the mainboard remove TR2 to eliminate any high frequency boost in the crunch and lead channels!?! I removed it folowing the advice which turned out for the bad after figuring out that transistor is what feeds back signal to the clean channel from the mainboard, I put it back and it works now, tho I do have the problem where there is still a signal present even with the volume all the way down much like DrGonz78 had...I was a little trepidacious to start pulling transistors to begin with, stupid mod site

[DrGonz78]

With Gain all the way down and Bass, Mid, Treble all set to 12'o'clock... Turn the Master Volume up and around 3'o'clock it would have a lot of hum to it on the clean channel. You might even just edge the Gain knob to 1 or 2 to and see if your getting that symptom too. If not I read about a guy that replaced the A200k Master Vol pot w/ a A220k to bring the bleed down a bit when volume is turned to zero. Anyway that guy said it kind of helped a bit, but this seems like a band aid not a fix.

Really my thought led me to think there was a ground issue from Vol pot VR5 on the clean channel board, Con4 on the clean board leads to Con 10 on the Lead board. So the Volume pot VR5 looks for a ground from the Lead board or that's how I see it on the schematic. So, I remember how hard that lead board was to get out the first time. I was worried it might have had a problem after taking it apart and back together again. So, many things it could be but it seems like something similar, symptoms wise, has occurred at least a few times that I know of now.

Yeah those amps are way beyond anything I ever want to work on again and the PCB board for the Clean, Crunch and Lead are not the greatest IMHO.

Edit: oh btw before I went into this amp the clean channel was normal. Turning down Vol and Gain and the channel was mute. So, it was not designed to do this... but man these amps clean channel seems to be a problem.

Double Edit: Maybe I was the problem since I had to get my grubby little hands on this amp. However, I like simpler amps w/ better PCB boards where it is more forgiving to work on. The Main power and output boards are great on these amp, but only before it has a runaway bias problem and melts away something.