Schematic for Marshall DSL40, board number DSL100M2-60-00-V6A

[aweste]

I just got in a Marshall DSL40 (not DSL40C or DSL40CR) with the main board number DSL100M2-60-00-V6A but I can't find the right schematic I've found the schematic for DSL100M2-60-02 but it doesn't match up.
The problem is within the 3-way standby switch (high-off-low), it seems to work alright in high mode but the low mode is totally dead. The switch itself is OK.

[The Dude]

I have only a partials, and it's V5, but it may be close enough and show the relevant circuit. You'll have to check.

DSL100M2-60-02-V5 Page2.pdf

[aweste]

Thats DSL100M2-60-02, not DSL100M2-60-00. But thanks for trying to help!

[g1]

Thats DSL100M2-60-02, not DSL100M2-60-00. But thanks for trying to help!

As far as I know, the board numbers do not match up with drawing numbers. The description for that drawing is 'main PCB'.

[aweste]

Hmm, you could be right! Anyway, I can't find the right schematic.

[aweste]

I just found out it IS a DSL40CR (the front panel only says DSL40, the back says DSL40CR. Unfortunately, it doesn't make it easier.

[g1]

Hmm, you could be right! Anyway, I can't find the right schematic.

Well, the way Marshall schematics are now, they all look 'wrong' because they are a nightmare. Lots of stuff that is not drawn 'properly'.
Look at the one from post #2.
Down in the lower left the switch is labelled 'on-standby-on'. That looks to be the hi-standby-lo switch. It connects to D12/D13 cathodes via CN8, D8/D9 cathodes via CN7, and CN9 connects to one end of R135 along with the OT center tap connection.
In 'low' position, CN9 should connect to CN8. If it's not working in 'low' either the switch is not carrying current (can still measure ok with meter and be bad), or you do not have voltage at CN8.
I would start by checking the DC volts at D12/D13 cathodes (+ end of C19).

[aweste]

Oh I'm so sorry! The schematic that The Dude posted in #2 actually seems to be the right schematic! I don't know why I ruled it out so quickly, I was probably a bit tired and frustrated.

Anyway, prior to this I did some backward engineering and figured out pretty much of the above. In HIGH position you have around 450 Volts on the CT, in LOW it drops to 200 Volts something (which I read somewhere is OK IIRC).

But then the standby switch is a double pole, the other pole is connected to CN90 and CN70 (Strangely enough the switch function isn't drawn, and the dotted lines shouldn't be there). This actuates the opto couplers which then is used to change the bias in the bias circuit in the lower right corner.
Seems like I'm on the track, thanks for the help!
BTW, I noted that the C21 cap is a bit bulged but a total failure should affect the HIGH setting as well. But of course I'll change it.

[aweste]

Turned out to be the C21 which is located after the switch. The HIGH power supply was powerful enough to maintain the B+, the LOW power supply was loaded down by the bad cap.

[Mars Amp Repair]

Here's the actutal service manual

[Indyryder02]

Here's the actutal service manual

That’s awesome! Do they have these for most of their amps? I’d love to have the collection of them to add to my files.

[Mars Amp Repair]

Technically as a warranty station, it probably says somewhere in the contract in the fine print that technically I'm not really supposed to disseminate them. I just do it here sporadically as needed to help everyone out.

[NakajimaYusuke]

Hi, I have a marshall DSL100H.
The problem you had is very similar to mine.

Low Mode doesn't work.
Capacitor C21 is broken.
These things are happening to me right now.

If you have already fixed the problem, please let me know what caused it.
I replaced C21 and C22 with new ones, but the problem was not resolved.
I'm desperate to resolve this issue.

[Jazz P Bass]

The DSL100H is a different animal.
The screen voltage is lowered through R111 to affect lower power.
I would verify the switch function.