Phantom power on Mod 50

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waldonreedjr

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After nearly 3 years of flawless performance the phantom power on my Mod 50 is no longer functioning. I did numerous tests (cable and component swapping) to rule out other failure possibilities, but it turned out to be the Mod 50. Everything else on the amp is functioning perfectly including all MIDI functions on the in and thru -- just no phantom power at the in jack. I'm just curious if anyone else has experienced this issue.
 
The fuse is probably blown. Plugging and unplugging a midi cable when the power is on may take out the fuse on the midi pcb. A similar thing happened to my RM4. Replace the fuse and I think you'll be all set.
 
I was kind of wondering if that might be the case, though I always plug in before powering. Do you happen to know if that fuse is a snap in design or is soldering involved (haven't peeked inside yet)?

Thanks,

Waldon
 
If the fuse is the same as the Randall amps, it's a round soldered 1.25A fuse. The fuse is on the small pcb with the midi connectors. The 4-position dip switch is also on this pcb.

I replaced the round "single use" fuse with a 1.30A Tyco PTC resettable fuse, so it will never blow again. You can buy these fuses at Mouser Electronics: Here's the p/n: Mouser p/n:650-RXEF065.

:rock:
 
Great news! I opened up the amp this morning to confirm that the issue was indeed a blown fuse. It's a snap in holder so I was able to pop in a replacement very easily -- phantom power is back!

For future reference here's a note from Bruce:

There is an internal fuse that I would assume has blown. It is
located inside right behind the MIDI jacks. You can replace it with a
1.5 to 2.0 amp slo blo type. Radio Shack should have them. Fuses don't
usually blow for no reason but since everything appears to be working
correctly, I would suggest replacing the fuse and see what happens. The
Ground Control does draw a fair amount of current and could have a bit
of a current surge at turn on that could possibly fatigue the fuse.
 
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