RM100 - No output

I took possession of a used RM100 today and it is not working.

I tried all different tubes throughout. I have a jumper in the parallel loop and exercised return/send on the serial loop.

If I turn up the module and give the master some volume I can hear an extremely faint sound that is so thin and strangely distorted that it sounds like a buzzer.

Any thoughts on what to look at next?

I also put my HD500 directly into the return of the Serial loop with the same result.
I tested all the fuses (3 inside and all 4 for the output tubes) for continuity and all were good.
I checked the tube bias and interestingly enough all four basically came up at 0 until I adjusted them into range. But still no change on the output.

Playing around a bit I turned up the master volume and something popped and I saw a quick flash around the OT (if the OT is the one more towards the middle of the chassis next to the fan). All the tubes stayed lit, but I turned it off after that. Not sure if I blew one of the fuses or something else.

Is the OT F'd in this thing?

Some more updates:

I have found a fuse under the midi board that is blown. Looking under the amp with the back panel to the left...it is the right one of the pair of fuses under the midi. Having trouble reading what its value should be.

I also found my output impedance selector was coming undone so I took that apart and reassembled.

Gotta get that fuse replaced, but wondering if that is the whole crux of my issue at this point or if I still have something bigger going on.

nitrous12 said:

I also put my HD500 directly into the return of the Serial loop with the same result.
I tested all the fuses (3 inside and all 4 for the output tubes) for continuity and all were good.
I checked the tube bias and interestingly enough all four basically came up at 0 until I adjusted them into range. But still no change on the output.

Playing around a bit I turned up the master volume and something popped and I saw a quick flash around the OT (if the OT is the one more towards the middle of the chassis next to the fan). All the tubes stayed lit, but I turned it off after that. Not sure if I blew one of the fuses or something else.

Is the OT F'd in this thing?

Click to expand...

I had a similar problem with my RM50 > Thanks to kc2eeb for the pic's and the help \m/ http://mtsforum.grailtone.com/viewtopic.php?t=19039 http://mtsforum.grailtone.com/viewtopic.php?t=12785&highlight=lots+pictures+rm50+repair

Well I have this much narrowed down...the 2 fuses under the midi board have both blown. At first it was the one on the right. Replaced it...nothing. Did another continuity check on the fuses and found the left one then blown. Replaced it and had the amp running at low volume (but sounding correct) for a few minutes. Put the chassis back in the shell and moved everything back into its place. Connected everything back up...nothing.

So I removed the chassis again to find both of those fuses blown again.
The impedance selector is definitely flakey. Although I was able to put it all back together and it worked ok when I did...its back to not sliding and notching in each position like it should. Its possible in screwing that back in place after I had it running that I moved it a little. I did check it when connecting everything again to fire it back up, but perhaps moving it has it screwed up? Could that be causing those fuses to go? I think they are the Supply fuses?

I am trying to search to see exactly what these are and what might be causing them to blow, but if anyone knows and can chime in I would greatly appreciate it!! The old thread from okstrat doesn't have pics any more.

This thread here is making me believe that funky impedance selector is the real source of my troubles.


http://mtsforum.grailtone.com/viewtopic.php?t=18141&highlight=impedance+selector

I had two arcs on the PCB due to the HV being too close to ground. Saw this on an old thread I dug up. One guy had his tech wire and jump around the problem. Another guy had the updated PCB sent from Randall that has more space between the traces where this happens but that was said to have been an earlier production issue that was corrected.
Thison I got was said to be newer so I assume the newer PCB. Just frickin strange this happened to me and never presented itself before. I wasn't even pushing the amp. Certainly starting with little confidence in this thing. I got it to see the difference between the Randall's and Egnaters and have a backup should my Egnater have an issue when I need it for live playing.
I guess we will see.

Just FYI, after I fixed mine it's been 100% reliable.

kc2eeb said:

Just FYI, after I fixed mine it's been 100% reliable.

Click to expand...

Did you have this same issue?

yep.

note to anyone who cares

-> Silicon Rubber


use Silicon Rubber around/over the traces to keep them from arcing

(and of course clean the PCB 1st with 100% rubbing alcohol to remove any carbon build up from the arcing )

easy fix :idea:

Silicon rubber is good. Regarding removing the carbon buildup from arching,
most of the time the arching will cause the PC board material to actually burn and turn to ash. That ash is conductive, in which case it has to be physically ground away. Of course, if it is only on the surface the alcohol will work. Best to use a magnifying lens to verify which or both.
There used to be a product called "corona dope" which was used to prevent arching in HV circuits like in old TV sets.