MP-1 3TM Boot Loop

[DissidentPenguin]

Hey guys,

I have a cople MP-1's (one stock and the other with 3T and Noise Mod), and the one with the 3TM started going in a boot loop. If I leave it on for a few minutes, it eventually boots normally, and it works normally unless I set the drive of any Overdrive channel to above 9. Any idea which part of the circuit to check? I suspect it might be an electrolytic capacitor that charges slower than it should or a regulator, but I would really appreciate some advise before I start messing with it. Is there any kind of service manual for 3TM mode? I believe it was originally performed by MarshallJMP. Any help would be greatly appreciated!

Best,
Carlos

[vansinn]

Sounds like the backup battery going dead.
Measure it's voltage; you'll likely find it's somewhat below 3 volts.

Before replacing it, do a backup of your presets.
It is indeed possible to replace the battery without loosing presets, but I don't remember the procedure; something like attaching  another 3 volt battery across the terminals, solder-out the [presumed] dead one, solder-in the new one, remove the external battery, and boot baby, boot ;)

IIRC, could also be the capacitor in the reset circuitry. Others will make me stand corrected if need be..

[rnolan]

As Van says, could be battery, anything below 2.7 volts (IIRC) needs a new one.  To be sure, I'd write the presets down (safest).  Also check the ribbon cable that goes from the front plate to the main PCB (carefully) if it's not seated properly it can cause some funny stuff (it also get quite brittle over time).  And last you can (again carefully) remove and reinstall the CPU (the really big IC) and/or the EPROM (with the version sticker on it), this is based on some experiences I had with one of my MB-1s (when you do this it should boot through full error checking, well did for me).  Apart from that it's MJMP territory (your cap theory could well be correct  :dunno: ).

[MarshallJMP]

That's no battery problem, usually either the wall voltage too low, a bad cap in the power supply, or the reset circuit.

[vansinn]

MJMP should be renamed to "OneLiner" ;)

I'll swallow the battery and do a reset..