Mark IV -lots of problems

[obican]

Hi

I'm from Turkey and I've recently bought a Mesa Boogie Mark IV Combo from a seller on eBay. Actually a friend of mine bought the amplifier for himself but because of his lack of technical knowledge, I'm in charge of the problem solving. Therefore, to keep things a little bit simple I'll talk as if I've bought the amp myself.

Anyway, the amp has some problems. First of all, it doesn't sound like it should, more like a 30 watt solid state amp running on a 18" speaker with volume knob gone to eleven(Muddy lows, almost no highs). I know that the amp doesn't sound like that but this is the least of our problems. The other ones are:

-Master volume knobs don't work. All three channels have a fixed master volume.
-The auto assign button on the right(Rhythm 2 - Lead) switches the channel to Rhtym 2 or Lead(has no effect when it's in the middle), regardless of any other settings on the amp.
-When you pull the Drive Level knob, where it should normally just brighten up the lead channel, it activates the master volume knobs for the channels.
-When that knob is pulled and master volumes are working, their volume levels are reduced from their non-working time. R1 is stays the same, R2 has slightly less volume but noticeable and Lead has 3/4 of the volume(when the master volumes are set to 10).
-When I select the lead channel from the back dial and I play with the Auto Assign switch, R2 position activates the R2 channel. Middle position has no effect(stays in the lead channel), Lead position still has no effect on the channel but channel LED on the Lead channel becomes brighter.

Since I live in Turkey, I can't just go to a Service Center. None of the repairmen here has ever seen this amp before, Boogies are quite rare here. Most of these problems are somehow related to the Fx Loop, except the sound quality and the push-pull issue. I have a limited knowledge of electronics but I checked the schematics which could be found on the internet and I have the impression that these issues could be related to the LDRs used in the amp. I'll probably give the amp to a very skilled repairman I know but he has never worked on a Mark IV before. Do you have any idea about the cause of these problems? Any suggestions?


Thanks for your help and concern

 

[Octavarius]

Wow, the amp is completely f*#$%d!! :shock:

Yes, sounds like some heavy LDR issues.

If he wants a new, functional Mark IV, I would send it to Mesa, despite the huge costs. These aren't 'regular' issues, and I would usually only trust the manufacturer to fix them. But that's me.

A very skilled technician in Europe, though, is Jonny (jvk on this board). He knows these Boogies very well, and would take very very good care of the amp. I'd trust him with my amp 100%. As he said himself "consider me as Mike Bendinelli's european protége".

I'm sure more knowledgable forum members will chime in on the specific details soon!

 

[ANIMATED SUSPENSION]

Wow !! Bad news !! Check what tubes are in it and where and advise please. It could just be a dying pre amp tube if you're lucky. The auto assign switches are just for turning the fx loop on or off for each channel not actually changing channels. you do that with the mode select dial or footswitch. Do all channels sound bad ? The knobs aren't loose on the shafts ?
Use the following settings for starters :
Full power
Pentode
Harmonics
Simul class
Mode select : FT SW (foot switch)
Graphic eq : On
Eq sliders in V shape
FX loop On Full time
Output level (pushed in !) on 1.5

Check each channel and advise what they sound like individually !!

 

[obican]

@Animated Suspension: As I stated before, the problem is not just the sound quality, I know what the auto assign switches are for, but they ARE changing the channels right now. Also the knobs are NOT loose on the shaft because they do work then the DRIVE LEVEL knob(pull bright) is pulled. Also all the tubes are new and tested.

@Octavarius: Thanks for your help and suggestions, sending the amp back to USA and to Turkey again would easily cost more than 600$, even if I take the amp section out of the combo. Someone in Europe would be a more considerable option. I dropped the amp to that guy I mentioned before, he'll just run some minor checking at first. Then we might decide what to do with it.

I was curious if this problem was common in these models. I had a Peavey Special 112 combo amplifier which would stop working if you sit on it. Later I found out that this was common in that model! I hope that it's just because of some stupid LDR malfunction or something like that. All the problems are focused around the master volume/fx loop section of the amp.

I'll update this tomorrow, if we find anything. Any kind of help is still welcome.

Thanks

 

[Octavarius]

@Animated Suspension: As I stated before, the problem is not just the sound quality, I know what the auto assign switches are for, but they ARE changing the channels right now. Also the knobs are NOT loose on the shaft because they do work then the DRIVE LEVEL knob(pull bright) is pulled. Also all the tubes are new and tested.

@Octavarius: Thanks for your help and suggestions, sending the amp back to USA and to Turkey again would easily cost more than 600$, even if I take the amp section out of the combo. Someone in Europe would be a more considerable option. I dropped the amp to that guy I mentioned before, he'll just run some minor checking at first. Then we might decide what to do with it.

I was curious if this problem was common in these models. I had a Peavey Special 112 combo amplifier which would stop working if you sit on it. Later I found out that this was common in that model! I hope that it's just because of some stupid LDR malfunction or something like that. All the problems are focused around the master volume/fx loop section of the amp.

I'll update this tomorrow, if we find anything. Any kind of help is still welcome.

Thanks

I've never ever heard of problems like these with any Mark. Most common ones I see here on the forums are usually tube issues. Sometimes caps and pot issues. Boogie isn't generally known for technical problems like switching/controls, etc. There is clearly something seriously wrong with the amp, and I'd find a experienced, trusted tech to deal with it.

Try dropping an email to Jonny and see what he has to say. You can find the contact form on his website; www.jvkamps.com. You can atleast get some helpful advice from him.

I'm currently sending my IIC+ to him for some repair and basically a rebirth for the amp. Completely renewed in almost every way, caps, LDRs, jacks, switches, cleaning of everything, etc. His rates are quite good too.

 

[kiff]

I had a Peavey Special 112 combo amplifier which would stop working if you sit on it.

It's a good thing Peavey doesn't make chairs.

(sorry, could't resist ; )

 

[6L6C]

Some of the problems you are describing are just plain strange!!

By any chance have you had the chassis out of the cabinet/headshell???
Put up some photo’s.

With problems like those it sounds like someone was doing some tinkering.

 

[ChrisCst22]

It's a good thing Peavey doesn't make chairs.

Actually I just picked up a solid ash model from my local GC. Good stuff. Well not really....But it's stuff.

 

[mr_fender]

Sounds like someone has modded the amp in a very bad way. Time for a good tech if you ask me.