Opinion needed on troubleshooting RM50 please-Relay problem?

[RomanMtz]

So I recently discovered that there?s a problem with the first module slot of my RM50. I didn?t notice it at first because I was mainly using a KH-3 in there with a lot of gain.

I noticed it when I installed a KH-1 in the first slot. There?s this weird grainy distortion that is very noticeable as notes fade out. As if you had a really crappy noise gate installed and it would cut out low signals with grainy distortion. This happens mainly at low volumes with low gain. If I raise the gain, volume, and play harder the problem is hidden but not eliminated.

This only happens on the first module slot. I have confirmed it?s not the module itself because if I install the same module on slot two it works fine. Also, installed by itself on slot one it works fine with the channel switch button pressed (like selecting channel 2 but since there?s nothing there, it still sends signal), but when I depress it, the problem returns.

From this test, I?m thinking the culprit is the relay that passes signal (RL2 on the schematic) when switching occurs.

I took the amp apart and physically all the connections looked good, no cold solder joints, shorts or open circuits. The blue slots where the modules are inserted look perfects as well (even used a little deoxit on the module and inserted it a couple of times to clean.)

Since relays are electromechanical and more prone to failure, I?m thinking that?s the problem. I was not able to find a direct replacement for the relays here (only could find in Europe) which it this one:

http://www.tme.eu/html/EN/subminiature-relays-rsy-series/ramka_1986_EN_pelny.html

But I did find this, which by the spec sheet, looks identical:
http://www.alliedelec.com/search/productdetail.aspx?SKU=70175802

Any opinions on my troubleshooting?

I can get some audio recordings of the problem if it could help? Thanks in advance!

 

[Jaded Faith]

Here are some thoughts in order of suspicion: RL1, RL2, Q1, C1, D1 all on the board the modules plug into.

The Omron GV5 you found is an acceptable substitute and was actually the original part used in those amps.

Hope that helps and good luck!

- Rob

 

[RomanMtz]

Thanks for the response Rob! Yeah, I'm 99% sure it's that relay. I have ordered a couple from Mouser and will be replacing them as soon as I receive them. I'll post back once I do.

Thanks!

Roman

 

[Jaded Faith]

My pleasure sir. Good luck and feel free to email me if needed.

All the best,
Rob

 

[roszatycki]

Roman,

If I was troubleshooting the amp I would do a couple things to verify the relay is bad. First, I believe that is a 12 volt relay so I would verify I am getting voltage to the relay to engage the internal contacts. Sounds like you are but a bad solder joint or failing component which Rob eluded to may cause the relay to act strange. Second, I would look at the data sheet or Randall schematic and simply jumper the signal path bypassing the effect of the relay altogether. If the problem still exists I would say it is not a relay problem. Not sure how advanced you are in electronics or if you feel comfortable trying those suggestions.

A few years ago I picked up a used RM50 that needed some repair work. It was one of the first generation RM50's that had some issues with high voltage arcing on the power tube board, typically with EL34's. Anyhow, I repaired it and used it for a period of time but eventually it arced some high voltage again and considering the $100 I paid for it and my purchase of an RM1250 I didn't bother with it much. Other than the high voltage issue, the amp functioned fine. I still have the entire module board in perfect condition if you wanted to try swapping the board. I would assume they would be compatible. If they are it would be a quick way of repairing the amp or if nothing else eliminating anything on that board as the culprit. PM me if you have any interest.

 

[RomanMtz]

Hey roszatycki, thanks for the response!

I performed a pretty extensive visual inspection of the module board (which isn't very populated anyway) for cold solder joints or other troubles and found nothing, but didn't really try firing up the amp while taken apart.

I am going to try to jumper the relay maybe next week (this weekend we have rehearsal) before I get the replacement relays. I'm almost 99% sure it's the relay, but you bring up a good point that it might not be the relay itself, but maybe the 12V signal used to activate it. Will keep that in mind while troubleshooting further.

Don't worry about high voltage disclaimers... LOL! I started out small modding Valve Jr's, but have modded and repaired several amps since then. Nevertheless, you never know when something could go wrong, so I'll take you up on that module board offer if need be. I'll let you know.

Thanks!

 

[RomanMtz]

So I replaced both relays... no go... same problem.

Will replace 2n4401, diodes and caps next. If that doesn't work, will test amp's voltages.

 

[RomanMtz]

Ok, I'm officially stumped... I replaced, both relays, both caps, both diodes and the 2n4401 transistor ant STILL have the same problem.

What has me really puzzled is that even if the module is in the first spot (nothing on slot 2), if selector switch in from of amp is pressed, there's no problem, if it's depressed, problem is there.

How is the signal routed when button is pressed and when it's not?

Can anyone clue me into this so I can try to figure out what could be going on?

I measured the 12V and 17V supplies and nothing unusual, only that the 17V supply was more like 19.5V.

I measured control 1 and control 2 from the module schematic and measured relative to each other, when button is depressed control 1 is 12V and 2 is -12V. When pressed it reverses.

Any help would be greatly appreciated.

 

[RomanMtz]

No one? Please?

 

[roszatycki]

Do you have an RM50 schematic ?

 

[fuzzboat]

Ditto - where is RomanMtz getting these schematics ???

I'm in dire need of a SL+ schematic

 

[RomanMtz]

Yes I do, I just can't quite understand how the signal is being routed with switch on and switch off...

 

[RomanMtz]

Ditto - where is RomanMtz getting these schematics ???

I'm in dire need of a SL+ schematic

PM me your email, I have an SL+ schematic, although I haven't verified if it's correct or not yet.

 

[fuzzboat]

PM'd
&
Thanx

 

[Jaded Faith]

The more I am thinking about this, the more I'd like to see a 3rd module for testing the issue. I really can't think of anything else it would be on the amp itself without having it in front of me to test with my equipment.

My suspicion is that it is related to the module or the slot. I am thinking it's either the slot is dirty (I know you cleaned it, but this is almost always the case in these situations where only one slot is acting up) or there is something about the KH1 PCB not matching up correctly with that slot in that amp (this is more common in RM4's, but I recently had a customer with the issue in an RM100 just last week).

The problem may be the length of that particular module on the part of the board with the traces. I hear about these problems 1-2 times a year. I wouldn't say it's common, as that's only about 0.005% of the modules I see annually through the shop.

If it's not better after a thorough blasting of compressed air followed by contact cleaner, try a 3rd module. If one is not available, I'd be happy to take a look at either the module or amp. There isn't much more I can suggest without seeing both and running some tests on my equipment in the shop unfortunately.

Hope that helps,
Rob

 

[RomanMtz]

The more I am thinking about this, the more I'd like to see a 3rd module for testing the issue. I really can't think of anything else it would be on the amp itself without having it in front of me to test with my equipment.

My suspicion is that it is related to the module or the slot. I am thinking it's either the slot is dirty (I know you cleaned it, but this is almost always the case in these situations where only one slot is acting up) or there is something about the KH1 PCB not matching up correctly with that slot in that amp (this is more common in RM4's, but I recently had a customer with the issue in an RM100 just last week).

The problem may be the length of that particular module on the part of the board with the traces. I hear about these problems 1-2 times a year. I wouldn't say it's common, as that's only about 0.005% of the modules I see annually through the shop.

If it's not better after a thorough blasting of compressed air followed by contact cleaner, try a 3rd module. If one is not available, I'd be happy to take a look at either the module or amp. There isn't much more I can suggest without seeing both and running some tests on my equipment in the shop unfortunately.

Hope that helps,
Rob

I really appreciate you chiming in here Rob.

There actually is a 3rd module... I originally had a Blackface module that I was using when I first encountered this problem. I decided to get a KH1 a fellow forum member was selling hoping that that was the problem, and no, same thing. I haven't confirmed this, but I'm pretty sure the same thing would happen with a dirty module, but it's not as noticeable.

When I was first troubleshooting, my first thought went straight to the socket. The thing is that let's say the socket is bad, then why when I have a module on slot 1 and no module on slot 2, it works fine with the channel switch button pressed, but it craps out again when I depress it (same with external footswitch). That's what has me stumped.

To recap what I've done, I replaced both relays, both diodes and the single transistor on the module board and everything is exactly the same.

I have to insist it has something to do with the signal path when the channel switch is pressed/depressed. I just can't figure out exactly how it's being routed in both situations... are you familiar with the switching circuit, Rob?

 

[Jaded Faith]

I just sent you an email. Please give me a call and I'll walk you through it on the phone rather than type out a book here.

All the best,
Rob

 

[RomanMtz]

After having a very illuminating conversation with Rob (much appreciated man!) I went ahead and ordered some parts... will keep everyone posted...

 

[RomanMtz]

So I've put the repair efforts on hold since we have a show tomorrow and I wouldn't want to mess anything up even more! LOL! But I believe I'm zeroing in on the problem... not the module board, with Rob's help, I've narrowed it down to the relay circuit on the poweramp board. Once the show's done, I'll take some voltage readings and report back.