Marshall JCM 2000 DSL volume problem

[dherm]

Within the last three weeks, my JCM 2000 DSL head simply stopped putting out any sort of considerable volume. I tried to tinker with the amp myself and after swapping out the tubes and a speaker fuse, using different cables and cabinets, and checking out the boards for burning or anything else indicative of damage, I'm totally stumped as to the cause of the problem. I haven't messed around with the transformers or anything beyond the above, but the problem persists and both channels are affected. Any suggestions ?? Thanks !!

[dherm]

Nothing so far . . . I'll check back later.

[Twist]

Do you have any experience using a multimeter or working around high voltage? If not it would be best to take it to a repair shop. It may be a blown plate resistor in the phase inverter section. There are several other possible problems. Without some initial voltage checks it's too hard to diagnose.

[Enzo]

And which JCM2000 DSL? 201? 401? 100?

[dherm]

My experience with anything electronic is fairly limited. I took it by a repair shop after checking some of the voltages myself. Turns out is was a resistor causing the trouble. I'm supposed to get the head back next week for an approx cost of about $25. Thanks for the help, though !!

[bnwitt]

Who dissasembles an amp, troubleshoots it, R&R's a resistor, tests the amp, and puts the amp back together for $25?? I wish Bill Gates would get out of the service business.

[dherm]

Jeff Jackson of St. Louis Computronics just gave me the quote yesterday. $25 was all he charged--he even sat there with me for nearly two hours explaining what had happened and just showing me the different components. It was a really cool experience.

[bnwitt]

You should tip him. He'll starve to death at those rates and he won't be there next time you need him.

[Amp Kat]

You should tip him. He'll starve to death at those rates and he won't be there next time you need him.

I'm glad I wasn't the only one that thought that. I felt kinda bad because I would and have charged much more for that repair. Then again I'm sure it's going to be one of those clip the leads and insert type which I have to say I'm also guilty of a few times.

[Enzo]

Either that or he is doing this on the side as some sort of favor or personal interest

[bnwitt]

Either that or he is doing this on the side as some sort of favor or personal interest

Yeah, it doesn't add up. Two hours of ratchet jawing and then the repair on top of that. At least 3 hours for 25$. Do the math. $8.33 per hour and that doesn't count the resistor, solder and cleaning materials. Those are Chinese wages. Better check the amp for melamine.

[Enzo]

I would point out that a whole lot of free assistance is doled out around here, only compensation being satisfaction.

[Tekwiz1]

Amplifier Repair

Jeff Jackson @ St. Louis CompuTronics here...I wanted to add some info to this thread.

When repairing an amplifier, it is important to start from the guitar/bass input with an oscilloscope and trace the input signal to the "failed" stage or section. In order to do this, it is important to have a solid theory of operational amplifiers, transistors, tubes, etc. In most guitar amplifiers (in my 27 years of repairing guitar/bass heads), the reason for failure is usually ten or more cracked solder connections on the underneath side of the main input circuit board. These heads get moved around often, causing lots of jarring and trouble for the main board.

I highly recommend against working on a tube amplifier unless you have experience in high voltage, as stated by one of other posters below...These amplifiers have plate voltages that range from 300VDC to 425VDC...This is enough voltage to stop your heart, stop respiration, etc...Much like a TV, a tube amp is very dangerous to work on.

Please refer your amp to a service professional. Most guys head straight for the tubes...however, this is rarely the case, unless the tubes are ten years old and have been played hard.

I serviced DHERM's amplifier because he had been around St. Louis to several locations...and his unit was still not working. I usually take "battered" customers in...and offer an explanation and understanding as to the issue. While I do not charge for estimates and offer quick turnaround times, I also wanted to mention that DHERM is related to a business associate of mine...So I went the extra mile for a friend.

Be Careful out there, Tube Technicians

JJ

[bnwitt]

I would point out that a whole lot of free assistance is doled out around here, only compensation being satisfaction.

Indeed. And you Mr. Enzo are now on my Christmas card list. I too have been donating my time and knowledge (for what it's worth) on forums for years now. The free sharing in here is targeted towards passing on the knowledge to the new generation though, not fixing things for free. I've been known to fix things for free from time to time for friends or folks in need too. Charity is very important.

[bnwitt]

I also wanted to mention that DHERM is related to a business associate of mine...So I went the extra mile for a friend.
JJ

Ok then. I feel better.