Marshall DSL100 replacement boards

[drewl]

Done a bunch of cutting and splicing to fix one of theses PC boards that become conductive.
Got the bias supplies stable but somewhere in the preamp its screwing up and failing.

Anyone know if the TSL replacement boards are compatible for the DSL's?

At a quick glance they look the same.

As a last resort if I can't find where this one is breaking down.

[g1]

Have you been through all this, including the newer stuff at the bottom? I know it's for TSL, but maybe some of it is applicable?
The Marshall TSL122 JCM2000 Repair/Mods Page

[drewl]

Are you kidding?
I was there at the beginning and helped with my findings.

This amp's board is by far the worse one I have ever had yet.
By isolating the screens from the grids and isolating the filament traces to the output tubes and running heater wires I got the output section stable.
I also had to relocate the phase inverter outputs away from filament traces and got that stable.
Now it appears the board is breaking down around V2 and V3, f-Ing up their voltages and causing hum increasing as it gets hotter.

I could try isolating filament traces to the preamp tubes but any confidence in this board is long gone.

Even if I think I have it right, who knows when it will fail somewhere else.

Like I said, this is the worst one I've seen yet.

[mikeydee77]

Done a bunch of cutting and splicing to fix one of theses PC boards that become conductive.
Got the bias supplies stable but somewhere in the preamp its screwing up and failing.

Anyone know if the TSL replacement boards are compatible for the DSL's?

At a quick glance they look the same.

As a last resort if I can't find where this one is breaking down.

I have bought a few DSL and TSL boards from Marshall directly. I did mix up my letters one time and was told they are not the same presumably minor difference than major. The 100w boards cost from memory about £70 to £80 here in the UK so for me it is a no brainer to replace.

[Mick Bailey]

The two boards are identical, but the component population is not. The TSL board has CON12, TR2, C27, R33 which are not present on the DSL board. There are also resistors fitted (R4 R5) where there are jumpers on the DSL board. There may be other component variations, but you would need to study the schematics to determine those.

So, not a straight swap.

[drewl]

Yeah, they're a bit more expensive here and so far vendors I normally deal with only have the TSL.

If the board is the same I can figure out the differences, just be a little more work.

Thanks.

[g1]

Are you kidding?
I was there at the beginning and helped with my findings.

Nope, not kidding, just trying to help. Sorry.
You're welcome.

[drewl]

I appreciate the help and was kidding.

It's by people helping each other on sites like this and that TSL site that we are able to find a major problem like this where Marshall had to admit their mistake and make replacement boards available.

[g1]

I appreciate the work that you and others put into this resource. It's very impressive and I usually try to link it whenever this topic comes up.
Perhaps there will be new material to add to it with regard to compatibility of the boards.

[Mick Bailey]

When comparing boards also make sure you're comparing the same revision - the boards changed slightly over the years.

[Alex R]

Have you been through all this, including the newer stuff at the bottom? I know it's for TSL, but maybe some of it is applicable?
The Marshall TSL122 JCM2000 Repair/Mods Page

I don't agree with Glenn Martin (rather a self-assured and assertive person it seems, not qualities I usually find reassuring in a technician - I wonder if he's on here?), at the very bottom of the page. He says the problem is with what I take to be the mute circuit caps, which cancel or reduce the signal post-PI. These do fail but that's not the bias leak problem. And the new board from Marshall does solve the problem, though one appreciates it's not so readily available outside the UK. I think that grinding the board away around pin 5 and wiring off the board is very likely to be a good fix - but in the end if you have the bias leak problem then you have a conductive board, I'd expect the issue to crop up elsewhere given time. So yeah, new board from Marshall if poss.

[drewl]

This board started breaking down everywhere which may happen to ones repaired previously.

As I mentioned I got the output and bias stable, then it started breaking down around the PI. Rerouting the pi coupling caps away from filament traces fixed that but it started breaking down around v2 and v3.

Who knows how long until it becomes conductive everywhere?

[Jazz P Bass]

My hat is off to you for the gallant attempt.

If the question is "can I get it close" then go for it.

If the amp needs to be reliable, I would put in a new board.

They are not cheap, Though.

https://www.tubesandmore.com/products/P-H219

Edit: interesting"fix" from dr Tube: Marshall JCM2000 Stable Bias Mod

[drewl]

That will fix the bias problem, and the early ones with negative temp coefficient resistors. Those you can tell hy the 220k grid resistors instead of the usual 5.6k

Well here we are a few years later and maybe those same repaired boards are failing in other spots?
That's what is happening with this one.

I heated the board at the preamp and v2 v3 voltages started failing, dropping quickly.

Like I said, I wouldn't trust them anymore.
Replacing the board is the only way to be sure.

[Mick Bailey]

Bias issues are not solely down to the main board; the bias board has to be considered as well and these are a common cause of failure due to solder joints breaking down.