Marshall JCM 2000-DSL50 output issue

[hiteck1]

Hi guy's
I have DSL50 here for repair that i had acquired from another technician that took a shot at repairing this amp. I received the amp with all the opamps fried. What he had done was he plugged up the secondary of the xfomer that supplies the +/- 15v incorrectly. Once i figured out what he had done i replaced the opamps and a bad ECC83 (V4) and then proceeded to check and make sure the wire harnesses were in there correct sockets. Well the amp fires up fine, bias is good, and i get a clean output on the scope with a 8ohm load and 1khz for the input. But the problems is i am not getting enough output. The most i can get is 2.8v across the 8ohm load. It seems all the voltages are there. Now i am thinking the tech had put the wires back on the output transformer incorrectly. Now the schematic does not show colors or the extra taps on the transformer so i am not sure everything is in the right place. Does anyone have the correct diagram on how to plug up the output transformer or maybe i need to be looking somewhere else. Also forgot to note i did change the output tubes and also i have used the return loop on the effects as the input to make sure its not the front drive board.-Thanx
Bill

[Jazz P Bass]

Marshall DSL 50

Can you measure the ac signal on the output tube grid.
If you have a nice healthy signal there, then yes, it looks like an output transformer issue.
Can you identify the colors?
Link:http://www.geofex.com/ampdbug/outtrans.htm

[oc disorder]

This may be of use
DSL100 | Jack PCB - Output Transformer Removal
Has a picture of a DSL 100 o/p trans in circuit which I think...????
has the same layout of terminals and wires with spade connectors.
Actually I'll attach the pic... for reference
Busted gear must have marked the colours on the transformer.
Nice touch..

[Jazz P Bass]

Marshall OT

Here is a link showing the wire colors.
On the left, is the output primary.
CT goes to B+.
3 & 1 go to your output tube plates.
On the right is the output secondary.
Black is ground.
Link:DSL100 | Choke Installation

[Amp Kat]

You should get about 35 ohms across the primaries and about 17.5 from CT to each side. Make sure you get that.

[Mark Black]

Try the 16 ohm output.

These amps use the (problematic) switching contacts on the "ground" (sleeve terminals) of that jack to feed the sleeve terminals of the two 4/8 ohm jacks.

Also very common to find cracked solder joints at the jacks & impedance selector switch (among others).

[gomez63]

Try the 16 ohm output.

These amps use the (problematic) switching contacts on the "ground" (sleeve terminals) of that jack to feed the sleeve terminals of the two 4/8 ohm jacks.

Also very common to find cracked solder joints at the jacks & impedance selector switch (among others).

So true!

[hiteck1]

Amp Kat gets the win

Thanx everyone for the pics and the advise. That helped alot. After determining that i had good grid signal and the wiring was correct i was not sure what the winding ohms should be but after AK numbers i came up with 71ohms across the primary and 29 and 42ohm from the CT. Sounds like the OT to me. So now were would be the best place to get one?
Thanx again!
Bill S

[Amp Kat]

That doesn't sound right , are you sure you have the right wires ? Look at the diagram here Hoffman Vintage guitar tube amplifiers, tube amp parts, tube amps, tube amplifier for MOP 50 and make sure you have the right wires. Those #'s don't seem right and take the tubes out also if they are in.

Also check this thread out below as it has some very valuable stuff from some good techs.

http://music-electronics-forum.com/t12900/

[hiteck1]

Look at the picture of the OT in this thread. On the side were the blue-purple -white wires are and assuming the blue is the CT those are the readings i get. These readings are with the wires off the OT. Am i measuring incorrectly?-Thanx

[Amp Kat]

No, you want red , & white across the primary with the brown as the CT. The Brown CT is also known as B+. If you put the meter on ohms and check from pin 3 of one socket to pin 3 of the other socket you should read the same as going to the red and white. The B+ (ct) doesn't go to the tube so you have to find a test point on the board to take it from like the HT fuse because the B+ supply cap nodes are underneath the board.

[hiteck1]

Hi KB,
There is no brown going to the output transformer. The wire that goes from the OT to to B+ is blue. My OT matches the picture in the link perfectly.-Thanx

[Amp Kat]

Marshall DSL Transformers

I think that is the same tranny that is in the JTM-30's hence part of the problem.

[hiteck1]

The one i have is more of a modern technology build. Tabs on the xfomer and a totally different wire color scheme. So the measurements you gave me should be the same outcome with the OT i have?-Thanx for the replies!

[Amp Kat]

If you hook it back up to the tabs and the blue and brown ohm out with continuity to pin 3 and the red does the same to the HT fuse then yes. What's strange is that both sides = the resistance total but they are unbalanced. from side to side. Usally for a 72 ohm tranny from CT to each side is 36 ohms or very close. Have never seen that with those trannys but it is possible so without doing a reverse voltage test from secondary to primary it's hard to say.