Marshall DSL channel switching issue..

ben1605

So I've got a 1998 Marshall dsl 50 and it makes a very audible pop when switching between the two channels, its currently with a tech who is struggling to find the issue. At first it was thought to be the ducking circuit but he's checked it over and it seems fine. I've tried disconnecting the reverb because some people say its that, no luck there.

Its more prominent with the mid shift out and with it in, its not noticeable to an extent and will go away after a minute or so (this is annoying because I don't use the mid shift ever)

Anyone else had this issue and fixed it?

ICBM

If it's affected like that by the mid shift switch, the cause is probably a leaking cap in the tone stack which is allowing a DC voltage through onto the MV pots, which are immediately after the tone stack and immediately before one of the switching relays - the change in DC voltage from one pot to the other when the channel switches will cause a pop.

I would suspect C20 (most likely) or C23 - on the controls PCB - since they each feed a pole of the mid shift switch which bypasses another cap when the shift is off, hence there is no further DC blocking and charge will build up. When the mid shift is on, these caps will block the DC and allow the charge on the MV side of the mid switch to drain away.

No doubt this all sounds like Chinese to you - so feel free to forward it to your tech. I might be wrong but it's where I would start.

ben1605

Thank you for that! i've forwarded this to my tech who said he was suspicious of a leaky component anyway

it also makes the same pop when pushing the mid shift in and out so it sounds like it could be those components!

siraxeman

years ago when I got a DSL50 head it developed this same fault inside a week from buying brand new..took it back n got a straight swap for another new head and never had the problem with it till I sold it. Now my DSL50 (in the guise of the limited edition 85th anniversary 1923C 2x12 combo) has never done this and so far in the last 6yrs only had 1 breakdown..........