Hello All

I am looking at a Marshall JCM800 Model 2205 ("old style", no chip) which suffers some problems. Mainly, the Boost channel sounds very gated and "splatty" with very low output.

It has been worked on by someone previously, who replaced the dual-gang gain pot and the volume channel pot on the boost channel. They also replaced some of the box capacitors with combinations of radial caps in series...looks like they didn't have the right value or couldn't wait to order the right parts.

I humbly request help with two things;

Would someone have a schematic or service manual for this amp that has the capacitor values listed by reference designator? The replaced caps are at
C8 C9 C36 C38 and C39, and the schematic (attached) doesn't list them that way.

Additionally, where's a good place to start with the issue on the Boost channel?

https://drtube.com/schematics/marshall/4210.gif