RM50 suddenly not working? Any help?

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tnjazz
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RM50 suddenly not working? Any help?

Post by tnjazz » Sat Jan 27, 2018 3:38 pm

So I just got my new module today (an old Stonerverb) and it sounds great through the RM50.

Just went to channel switch and now I have no sound and the module lights are off (neither module works). The amp power light is still on though.

I had the speaker out connected to a Two Notes Torpedo Live and I was testing out the headphone sound. It's my understanding that the Live provides an 8 ohm reactive load to the amp, so there shouldn't be a problem there (amp was set to 8).

Anyone have any ideas on what to troubleshoot? I've tried turning it off and on again, reseating modules, etc.

Could I have somehow nuked a transformer?

warmachine67
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Post by warmachine67 » Sat Jan 27, 2018 4:56 pm

Maybe someone else will chime in, but aren't some internal fuses hidden inside an Rm50?

I'm guessing you tried plugging the speaker back in? Was there any hum with the speaker plugged in?

Was there a pop or noise when this started?

tnjazz
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Post by tnjazz » Sat Jan 27, 2018 5:14 pm

I'm about to pull the chassis and look around inside (carefully).

If I patch my AX8 line out into the amp return I get sound if I crank it up. The power tubes look good.

It appears the first 2 preamp tubes in the amp are not getting any juice. The third tube (nearest the power) is glowing though.

So I'm thinking there might be a fuse for the input section that has gone out?

Anyone know?

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Post by Mattfig » Sat Jan 27, 2018 5:17 pm

Power tubes getting any power? Oops.....Just re-reading this....

There are fuses inside, I will look for a schematic. There is an input tube V1 that is nearest your input jack....The middle on is your Loop buffer, and the one closest to the Power Tubes is you Phase Inverter....Unlikley to have those fail....
Last edited by Mattfig on Sat Jan 27, 2018 5:21 pm, edited 1 time in total.
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warmachine67
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Post by warmachine67 » Sat Jan 27, 2018 5:20 pm

I seem to remember there are four small fuses on the power switch side of the chassis hidden when it is boxed. I am not sure what they do.

At least it still makes sound :) and it seems your OT is ok.

Sounds like whatever has your modules not working has the first two preamp tubes not working.

I'm curious what you find.

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Post by Mattfig » Sat Jan 27, 2018 5:23 pm

I have a schematic, where shall I send it?
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tnjazz
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Post by tnjazz » Sat Jan 27, 2018 5:28 pm

Mattfig wrote:I have a schematic, where shall I send it?
You can email me at tnjazzgrass AT yahoo

I can't read a schematic though. I have pretty much zero knowledge about amp guts so I doubt it helps me but who knows?

I've got the chassis pulled and all the visible fuses I see appear to be fine. Haven't tested them but I don't see anything obviously wrong.

V1 and V2 are not getting anything. V3 is, however. About to fire it back up again outside the combo to confirm this.

warmachine67
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Post by warmachine67 » Sat Jan 27, 2018 5:33 pm

Guess you have some spare 12ax7s to try in v1 and v2? Probably the same result.

I'd have to see a schematic if the internal fuses are ok before I could even begin to guess what next.

tnjazz
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Post by tnjazz » Sat Jan 27, 2018 5:38 pm

Yes, I've got plenty of tubes. The ones in the amp were actually not the ones in it when I got it.

I did swap out both preamp and power tubes this morning. I had a JJ 5751 in V1 which should have been fine I would think. I just put the originals back in and V1 and V2 are definitely not seeing anything. V3 is, however.

Also put Mullard EL34's in place of the 6L6 and biased the amp to 30.

tnjazz
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Post by tnjazz » Sat Jan 27, 2018 5:56 pm

Just posted that I thought one module slot was not getting power but in fact after swapping slots it is.

That particular module has a much weaker tube complement so it didn't appear to be working but that is not the case.

So Back to square one.

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Post by Mattfig » Sat Jan 27, 2018 5:59 pm

So fill us in, do the module lights in the front work?
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Post by Mattfig » Sat Jan 27, 2018 6:01 pm

Definitely check the fuses you see for continuity....They can appear fine but still be shot...
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Post by tnjazz » Sat Jan 27, 2018 6:02 pm

No module lights, no. Tubes appear to be heating up in both slots, but no lights on either module.

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Post by Mattfig » Sat Jan 27, 2018 6:05 pm

What if you pull the cable to footswitch and try to switch in front?
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tnjazz
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Post by tnjazz » Sat Jan 27, 2018 6:08 pm

Yup already tried that and no dice there either.

Here are a couple pics of what I’m seeing so far: no lights on the modules, power tubes and V3 working but not V1/V2 and tubes in both modules working (slot 1 is working although in the photo it’s hard to see).

https://imgur.com/a/951f1

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