MP-1 Hum, Hiss, Troubleshooting

Hi,

I'm writing in hope of getting some help troubleshooting my MP-1. I had done the Noise, Battery, and Marshall mods and loved the thing. It was my "home amp" and I ruined it. I was attempting to convert a speaker output on my Wurlitzer 140B electric piano to a line level or preamp output and (like a complete idiot) I plugged it into my MP-1 to test it. I got a pop and a couple sparks on the MP-1 from around the power section and at the front at the input jack. I know. Idiot. So now I get a terribly loud hum and a persistent hiss when it's turned on. It also seems like the bottom half of the frequency range may be missing (something like everything under about 400 or 500Hz I think).

I have gone through the whole thing on a couple of occasions and replaced my mods (the three caps in the power section from the noise mod, the 3 caps in the tube section, 3 or 4 transistors from the tube section and a couple on the main board in the same area, about 6 of the opamps including the headphone, effects loop, etc - U4, U8, U9, U10) and did a little better quality work on it than I did the first time. The only things I have yet to replace are the tubes (both are lighting up fine and don't appear to be damaged at all from visual inspection), the 6 diodes in the power section or the 4 in the tube section and the transformer.

Is it likely that my problem is the transformer or would it even be coming on if the problem was there? Are the diodes more likely to be the culprit? Or is there something else that more commonly causes this symptom?

Thanks for any input you may have on this. I really appreciate it and I hope to resurrect one of my favorite pieces.

All the best,
Ben