OK. I resisted the urge to spray hot solder and got a meter to check the IC voltage.

The only two pins that gave me a reading were on opposite corners, I think the + /- Vcc pins.  I got -13.68 and 13.81. The readings fluctuated a little bit measuring them again, -13.87 and 13.78.

Thanks Jazz and Enzo for having a look
    I dont have any testing equiptment yet to measure the IC output voltages. I'm just getting into making my own pedals and will have one soon. Just from looking in the amp-which is similar to the Guv'nor pedal, I could see parts were missing from the scematic. I'm glad it isn't a problem, but plan to return it to stock
   The sound quality isn't good-even though the amp works. Replacing the speaker did make a noticable difference in opening up the high end, but there is still an unpleasant and unatural sounding distortion as the note decays.
     I Have the new 500k rev log pot, but haven't installed it yet. I'm waiting on a parts order for the 1N914's. But the preamp and master gain work as expected.
    The low input jack was pushed inside the chassis so it couldn't be used, but is jumpered to the high sensitivity jack.There is no oscillation from the high gain jack. The preamp gain doesn't do much until the 8-10 range, as expected. Not sure if someone tried a jumper mod on the inputs, or if it is stock-on the scematic there is only one input jack.

My alpologies, here's a link

  http://www.drtube.com/schematics/marshall/5010.gif

Total noob here, with little electronics experience beyond wiring guitars. I just picked up a 1982 Marshall Master Lead 30 combo for 50 Euros, so it's not like I was expecting much. I had a Lead 20 back in my teens that I remember liking alot, but this thing sounds like a moist fart.
   I opened it to clean it out and saw that D2 is missing entirely and D1 is not a diode, but a 2n2 Cap. Someone has tagged the bottom of the chassis with a permanent marker W.A.M Workshop And Music.  Has someone actually done something clever, or really stupid? Even on low gain setting there is an unpleasant 'fizzy'coating. I gave W.A.M the benefit of the doubt and swapped out the Red McKenzie out for a Celestion G12L, which made the moist fart sound like a bit more carefully executed fart, so now I'm leaning toward stupid.
I've researched the other 5010 posts here, and bought a 500k reverse log to replace the V1, but now I'm wondering if it's worth the bother. Looking at the Schematic, D1 and D2 seem to have something to do with Voltage supply, and I wonder if this mod hasn't burned out something else. The amp powers up and seems to work  - it just sounds more like a 1-knob, particle board starter amp from an old Sears catalogue than a Marshall.
    I'm going to go ahead and replace D1 and D2 with fresh 1N914's, and hope that helps. Is there anything else I should worry about? Like maybe R23/24 and C19/20, which seem to be in the same loop? Would this mod have ragged out the op-amp? What would the point of such a 'mod' be? A poor man's variac?
    Sorry in advance if I'm wasting anyone's time, but certainly would welcome some insight.