Hi, Phil. Mine looks very similar, only the two input jacks are verticle, and there is no line out/headphone jack. I'm not at home, but will get some pics when I get back tomorrow.

I got an e-mail back from Marshall. They won't give out a schematic, or even confirm there is an alternate version. If I want it returned to stock, I have to send it to them.

If you think there were clipping diodes in there originally, I would be interested in putting maybe a yellow Led on D1, and a pair of germanium diodes across D2 for more asymetrical clipping, but I don't want to start a fire if it's not for clipping.

The pic isn't the best. What's going on is that ends + and - ends of both D1 and D2 have been jumpered together on the bottom of the board.

Thanks Enzo! I contacted Marshall about another version of the scematic. They said they have the a schematic, but can't gaurantee what version it is, and will get back to me. I haven't heard anything further. I finally got under the circuit board, and D1 and D2 seem to be linked together.

Yeah, I have I think the earliest version. The only schematics I can find are dated 1988 to 1990. 2 vertical inputs, but no  DI or headphone out.

Ok, I found a Teemuk post about biasing. Looking over the schematic again, I'm wondering if D1 and D2 have something to do with It. That might explain why D2 is missing and D1 has been changed to a small value cap.

Thanks Phil!

 I hooked everything back up to test it like you suggested,and that's EXACTLY whats happening - no matter which input, no matter how clean I dial it in, I still get that farty speaker-fizz.

Here's another obvious replacement.

It works-It just has an unpleasant sound. Even on the lower gain input there is a cruddy blanket of harsh fuzz wrapped around what would otherwise be a useable tone. Some of the parts seem a bit 'aftermarket'.

Things You Can Tell Just By Looking At Her:

I found alot of electrolytic caps on the board that are not the same value as the scematic.

C2 is supposed to be 0.1p, its 2,2u, 125V

C13 is supposed to be 47n, its 100uf, 125V
c14 is supposed to be 2u2, its 100uf 25v
c17 supposed to be 100u, its 100uf 25v
c18 supposed to be 470p, its 22uf 25v

c11 is supposed to be 47n, its a strange looking disk, with 5000 printed on it
c12 is supposed to be 220p, its .047 orange drop

c20 is supposed to be 100p, its 2200uf -35V
C21 is supposed to be .22u, it's 2200uf 25v

I'm certainly willing to admit I could have set the meter wrong. I just got it in yesterday. I followed the manual and set the dial to V symbols, but aside from that not sure if it's dialed in tight.

I reversed the probes, which gave me a reading of zero at the + Vcc pin, and every other pin but the -Vcc, which read 28.8. Switching the probes again gave me 0 across all pins but the +Vcc, which read 28.8 to 29.0.

I got zero's across all but 1 of the pins. I think pin 8 is the Vcc+, which read 28.8. It gave me alot of fluctuations from 0 to 5, 16, etc, but 2x it gave a stable 28.8 reading.