Aaargh! No sound Rm100 Making me nuts!

[VOD]

I powered down my Rm100, and it was working fine. Powered it up today, no sound. I've diagnosed as well as I can for several hours and it's baffling me!

Here's what I've done, any suggestions or thoughts on the problem are more than welcome.

Current condition is - Powers up, lights on, fuses glow, fan on, no sound from mains. I DO however get sound from the preamp if I go straight from the effects loop into an impulse modeler (Computer). I believe it narrows things down to the power amp section.

The only response I get at all is if i get the master section near max, the power tubes rattle and make a staticy version of what's played, so they are getting something to them.

I've-
Switched all cables and speakers

Checked each tube. All look good, no failure lights on amp either

Checked fuses for tubes and internal. All pass the visual test, but I don't have my meter here to do a definitive check.

Cable looped both effects loops, no result.

Any thoughts? loosing hair by the minute!

 

[kc2eeb]

Check the speaker impedance switch. Move it back and forth and then to the proper setting. Make sure it's not broken.
VERY important. If you're hearing the tubes rattle and no sound is coming out of the speakers, STOP! You can blow the output transformer!
Then check the cables with a meter, for continuity and shorts.
Make sure you have the speaker plugged into the "use first" jack.
It sounds like you have a defective cable.

 

[Jaded Faith]

Everything mentioned in the last post, plus be sure to remove the PI tube (the 12AX7 closest to the power tubes) and put a different tube in there. If it's not a bad cable, I'll bet your PI is bad.

 

[VOD]

Thanks for the help guys. Still no luck though. I had already swapped all the cables, and switched speaker cabs as well. Checked impedance switch, it's working and set correctly. Speaker cable is in "use first" output.

I've already cleaned all the jacks.

I just replaced the PI tube, still no sound. Any other thoughts? This one has me stumped!

Thanks again for the advice thus far.

 

[kc2eeb]

Next, with the amp OFF, plug a known good speaker cable into the "Use first"
speaker jack. Then, measure the resistance from the tip to sleeve as you switch impedances on the impedance switch. I don't recall the exact readings you should get but the highest ohms should read the highest, and progress lower to the 4 ohm setting. If you read open or no ohms on any measurement then either the O.T. secondary winding is open or shorted or the switch is defective.

 

[VOD]

I think we're on to something. I did the resistance check as you instructed and I got no change in reading on all three settings. Each read 2.6. Checked back and forth 3 times, and no change for 16, 8, or 4.

 

[kc2eeb]

OK. Are you on the low ohms scale? What I'm looking for is, does the reading
= 2.6 Ohms or is it 2.6 x 10, or x 100, or 1K?
Also, to eliminate the speaker cable resistance, if you have a phone plug with no cable attached to it, plug that into the speaker jack instead of the cable.
A speaker cable can have .2 up to almost 1 ohm resistance by itself.

 

[VOD]

Whoops! Sorry, that probably would have been good info to include!

It was 2.6 reading at 200k setting.

I don't have a phone plug unattached at the moment, but if needed I can pull on from a cheap cable here. Thanks for all the input.

 

[kc2eeb]

2.6 on the 200K range would be 2600 ohms which is way too much.
If you are using an analogue meter ( one with a needle pointer and not a
digital read out) set the ohm range to it's lowest setting, short the two test leads to each other and use the adjustment pot to zero the meter.
Then, try the test again.
If it's a digital meter, set it to it's lowest ohm range ( switch it out of "auto")
and short the test leads together. You should get a reading of .01 or .02 ohms or so.
I just measured a spare O.T. for my RM50.
The secondary winding (the speaker output winding) measures around
.4 ohms at 16 ohm setting, .3 ohms at 8 ohm setting and .2 ohms at the 4 ohm setting.
These are TENTHS of an ohm measurements.
Very important that you zero the meter before you test.

 

[VOD]

Okay, I shorted the leads (using a digital meter). I'm also now using a jack with no cable attached. At lowest ohms I'm getting absolutely no reading in any of the three positions.

 

[kc2eeb]

By no reading do you mean 0 ohms or infinity?
Also, what brand and model meter are you using?

 

[VOD]

No reading meaning infinity - no difference in reading from when the probes are touching nothing.

This is the meter i'm using - http://www.home-protectors.com/ProductDetails.aspx?5

Not the best, but i;m away from home and had to grab a few tools local!

While inspecting the ohms selector, I noticed it seemed to be awkward and after several movements the assembly became disjointed. I'm beginning to think this could have to do with the issue. Popping open the assembly a few pieces came out quickly, so I need to make sure it goes back as it should. I'll get a pic of the parts.

 

[kc2eeb]

Bingo, to use an old expression.
Your meter is good enough.

 

[VOD]

Here's the parts. Hopefully nothing has gone missing from the assembly.

 

[VOD]

Everything in the assembly makes sense to me except the V shaped copper spacers. Any tips?

 

[VOD]

Victory is mine!! After getting the switch housing back together, it fired right up. I would have been sunk without the help. Thanks so much guys.

Especially kc2eeb. You went above and beyond for a stranger! If you have a paypal address, PM it to me, and i'll put a little something in the tip jar to say thanks. :wink:

 

[kc2eeb]

Yep.
I'll give you the order of the way the parts stack with the fixed contact board
(the part with the wires soldered) on the bottom.
The two silver pieces, right below the square spring in your picture, go first
with the smooth curved bottom facing the fixed contacts. (like a sled on snow) The V shaped copper "spacers" are the sliding contact springs. The point of the v goes towards the sliding contacts. the top of the v goes towards
the sliding plastic finger piece. There should be recesses in the finger piece to
hold them in place. Then, the rectangular spring with the rectangular cut out
(the top most part in your picture) goes ON TOP of the finger piece with the
point of the v notches facing up. Then that all goes into the metal housing
(the rightmost part in your picture). Make sure the whole assembly slides back and forth smoothly and clicks into the 3 detent positions BEFORE you
re-crimp it in place.

 

[kc2eeb]

Got it together already. Great!
And...no need to put anything in the tip jar. Just glad to help.

 

[VOD]

Well, that's really kind of you. I hope I can return the favor at some point, I definitely owe ya one. Cheers.

 

[JD]

Hey VOD, now you're discovering why this is the greatest forum on the Internet. There are some awesome people around here helping each other.