Does anybody know about RM4 electronics/schematics? My RM4 has developed a very loud grounding hum that can be totally solved by physically jostling the amp, so there's a bad connection. I opened it up and did not find any lose wires and the AC outlet ground is making connection to the chassis. The grounding switch has no effect.
Severe Grounding Hum in RM4
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3 Mile Stone
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I'd recommend a PM to RD Rich or RD Steve, two forum members who are here that work for Randall. I think they can help. I know that Egnater stands behind their products but it's pretty well known that they have a LOT on their plate right now. Probably a little too much too do the actual repair, but if all else fails they will be glad to talk to you or a tech to assist with repairs I'm sure.
I have a Randall RM4 that I have isolated a grounding problem with and it is causing a hum that I cannot get rid of by simply playing with ground lifts. Is there anyone reading this that is in Nashville who could help me correct the problem? I think it is something simple, but I am not the guy to tackle it.
thanks,
Scott
thanks,
Scott
GtrGeorge!
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I am not an electrician..so take my advice with caution..
a few weeks ago I had a bad groiund hum...but it turns out it was because I had a bunch of rack things and they were all competing to be the GROUND.
I got everything on one outlet strip (I had to lift one 3 way plug into a 2 way..) and the hum was gone.
And yes, my hum could be halted by smacking my rack on the side..but that was because my rack was connect as ground .
so: get an electrician or electronics person to look at your grounding IF YOU ARE RUNNING MULTIPLE POWERED AUDIO DEVICES.
For me, the gear was not broken..just improperly used.
a few weeks ago I had a bad groiund hum...but it turns out it was because I had a bunch of rack things and they were all competing to be the GROUND.
I got everything on one outlet strip (I had to lift one 3 way plug into a 2 way..) and the hum was gone.
And yes, my hum could be halted by smacking my rack on the side..but that was because my rack was connect as ground .
so: get an electrician or electronics person to look at your grounding IF YOU ARE RUNNING MULTIPLE POWERED AUDIO DEVICES.
For me, the gear was not broken..just improperly used.
That is good advice, and something I learned a while back was to have all your stuff into one outlet when troubleshooting ground issues.
I have now confirmed it is not a ground issue. We hooked it up at the shop and there is an internal issue with the RM4. I will post the solution once we have made the correction (after I make sure that it works).
In my case, the hum is always there, but gets louder if you use the POST out verses the PRE out.
I have now confirmed it is not a ground issue. We hooked it up at the shop and there is an internal issue with the RM4. I will post the solution once we have made the correction (after I make sure that it works).
In my case, the hum is always there, but gets louder if you use the POST out verses the PRE out.
GtrGeorge!
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...then I am not sure whats wrong.
Id get the schematic and then turn that and the amp over to a repairman you trust.
Id get the schematic and then turn that and the amp over to a repairman you trust.
Bewitagos1
Well-known member
GtrGeorge! said:
good chance its a cold solder joint or a broken trace problem. if it were mine, considering I know a little bit about boards, I'd take off the top of the RM4, power it up and try to isolate the component with a non-metalic probe, i.e.; pencil and gently, repeate, gently start tapping on components to find which one is connected to the hum. if its a cold solder joint, a spot of solder with a hot iron will get you back in business. if you don't possess the skill to solder, best to leave it to someone who does.
Good Luck!
Jimmie
I wanted to follow up on this in hopes that it will help anyone else who experiences the problem. After narrowing down the issue was within the RM4 and was louder on the POST out, I contacted Bruce Egnater, who told me exactly what the problem was:
"I'm going to take a guess and say it is possible the high voltage regulator transistor may be shorted. It is a TIP50 transistor that is attached to the smaller upright heatsink on the power supply board. To check this, carefully measure the high voltage on the collector of the transistor (which also is the heatsink). Should be between 315VDC and 330VDC with the four modules installed. Measure the regulated voltage at any number of places, which is easily determined from the schematic. It should be right around 300VDC. If it measures within a couple of volts of the raw supply on the collector, the transistor is shorted and is the source of the hum. If the measurements are as stated, the problem will be elsewhere. You must do this test first to determine if it is the problem."
Sure enough, we determined that is -exactly- what the issue was. I confirmed it with Bruce and he is such a great guy - he sent me a replacement part at no cost. It was replaced today and I have confirmed the hum is gone (although I do still have to lift the ground on the RM4).
The replacement part Bruce sent was a BUL216, which is a higher voltage rating part.
If you have confirmed your RM4 has a hum that you know should not be there (and the best way might be to test it against another RM4), try having a qualified person check the stuff above. Because we narrowed directly in on the problem and saved all that time, it was less that one hour from tip to tail on getting it fixed which saved me a lot of $$$.
Bruce has created another Egnater customer for life!
Scott
"I'm going to take a guess and say it is possible the high voltage regulator transistor may be shorted. It is a TIP50 transistor that is attached to the smaller upright heatsink on the power supply board. To check this, carefully measure the high voltage on the collector of the transistor (which also is the heatsink). Should be between 315VDC and 330VDC with the four modules installed. Measure the regulated voltage at any number of places, which is easily determined from the schematic. It should be right around 300VDC. If it measures within a couple of volts of the raw supply on the collector, the transistor is shorted and is the source of the hum. If the measurements are as stated, the problem will be elsewhere. You must do this test first to determine if it is the problem."
Sure enough, we determined that is -exactly- what the issue was. I confirmed it with Bruce and he is such a great guy - he sent me a replacement part at no cost. It was replaced today and I have confirmed the hum is gone (although I do still have to lift the ground on the RM4).
The replacement part Bruce sent was a BUL216, which is a higher voltage rating part.
If you have confirmed your RM4 has a hum that you know should not be there (and the best way might be to test it against another RM4), try having a qualified person check the stuff above. Because we narrowed directly in on the problem and saved all that time, it was less that one hour from tip to tail on getting it fixed which saved me a lot of $$$.
Bruce has created another Egnater customer for life!
Scott