Two Randall's with issues...

[christianguitarman]

Alright, having some issues. First I've got an RM80 that's created quite the buzz over the last few weeks. Even when no cables are plugged into the amp I'm getting a pretty loud buzz. I play at church every week and we had to not use my amp this past week because it was so bad in the sound system. I ended up plugging my pedal board into a sansamp... I replaced the power tubes and thought it worked. The next day it came back. I've tried almost everything. Switched all modules, switched the power cord, switched out the power tubes, the 3 buffer tubes... Nothing works. Again, buzz is there whether anything is plugged in or not.

2nd issue, my RM4 is not producing any output. As I was playing one day I heard a loud pop. Really loud pop. A couple days later the same thing a couple more times. It quit for awhile then a few days later the same thing and it quit producing output. Any ideas of where to start looking for the issue or has anyone ever experienced anything like this? Two broken Randall's is frustrating... Really frustrating

 

[Jaded Faith]

My first hunches are a bad high voltage regulator on the RM80 and a bad cap in the RM4.

 

[Mattfig]

Yep, if you are comfy with digging around a bit, sometimes these issues aren't too hard of a fix...And there's a lot of guys with tons of great info to help- my guess is that Rob's hunch is correct.

You might see some minor damage or something obvious telling you where to start....

Good luck!!!

 

[christianguitarman]

My first hunches are a bad high voltage regulator on the RM80 and a bad cap in the RM4.

So I think you've got it pretty close... when me and my buddy took the RM4 apart he thought it was a capacitor too. I'm not really familiar with testing capacitors or the best place to buy replacements. Any input would be greatly appreciated.

Also, on the RM80 I think it is a power issue just not sure what... I did notice that when I bumped the power chord by accident the buzz went away. Jiggled it and it came back. Tried a different chord but it didn't keep the buzz away. As I played with the cable the buzz crackled and would get better or worse. Also if I lightly hit the top of the amp in the back right corner above the power supply I found that is the fastest way to get rid of the issue. Thoughts or suggestions on how to proceed?

I appreciate all the help as I'm pretty much a noob at amp repairs... been alot of fun reading, troubleshooting, and learning though!

 

[christianguitarman]

http://youtu.be/ds68dueg_Kk

Here is a video of the issue. Sometimes when I do this the buzz goes away for the rest of the time i'm playing it. Other times it comes back within 10 minutes.

 

[christianguitarman]

While playing at church today I noticed that every time the drummer hit his floor tom or kick you could hear the buzz / a crackle in the amp. It was sitting close to him so he could hit the corner with a soft drum mallet if it started buzzing. Quite a pain.

 

[Jaded Faith]

That definitely sounds like it's a power issue. I'm going to assume it's either a broken power receptacle on the back of the amplifier or the mains ground has come loose from the chassis. You should open the amp up and check both to see if they are damaged on the inside. I would replace the Jack and I would probably go ahead and tighten down the grounds on the chassis.

 

[christianguitarman]

Took the amp out of the cabinet and didn't see any damage on the power receptacle. All of the wires seemed fine and all of the connections looked good. Plugged it up while it was sitting on top of the cabinet... Not a peep. Put it back in the cabinet and instant buzz. Decided to take the amp back out while it was still plugged in and the buzz seemed to be intermittent. I wasn't able to pinpoint it to a specific part while I was holding it. Seemed like it could have been linked with the two large black metal things on the bottom of the amp, not really sure though...

 

[warlok]

Large black metal things = Power and Output Transformers I assume? Poke them with a stick (lol). But seriously that's what I would probably do. If you think it's a transformer and intermittent, and have it open and plugged in, use a chopstick or the like to poke around a bit by those connections and try to duplicate the problam and nail it down to a particular wire/connection.

 

[Jaded Faith]

Are any of the ribbon cables or interconnects making an intermittent contact or receiving pressure from the top of your head shell? Your comments about it behaving outside of the shell point me in that direction.

 

[christianguitarman]

I'm not sure. Here's another video with it outside of the cabinet... I decided to try contacting some of the different parts to see if I could pinpoint the buzz. Watch all the way through as the buzz just inexplicably stops toward the end

http://youtu.be/LPak8nvrV2M

 

[Jaded Faith]

If it were here on my bench, I'd be focusing on either something wedged under your PCB's near the AC power input (that back 1/4 of the amp where the chopstick had the most noise) or a faulty part in that area. My money is on one of those two issues.

 

[christianguitarman]

Appreciate all of the advice! I'll continue looking in those areas. If I can't fix it there is a guy in town that builds amps but he stays pretty busy