Any experience with the Marshall JMP-1 (and how to take them apart)?

[Rockhorst]

I've been assembling a 6u rack unit for 80s metal and hard rock toonz. The JMP-1 I bought second hand has some problems. It sometimes loses about 20dB of signal level. Not fully intermittent, but very annoying and unpredictable. So far I've concluded that the input jack could use a replacement (ordered it, it's an odd ball part, mirrored from the standard switched jacks). The tubes inside are still the original Marshall ones, so I'll replace those as well. That may solve all my problems. However, there's also a 3.2V Lion battery inside that maintains the presets in the memory and will need to be changed periodically. Here's the thing: I can't get the circuit board out (at least, not in one piece, I suspect) and can't find a service manual, step-by-step guide or whatever.

So, any JMP-1 users here with some experience with taking the unit apart and modding it? There's really very little on the net to be found.