Marshall JCM2000 problem

Skywalker

Hi everyone.

I've owned and used my trusty Marshall JCM200 TSL100 2x12 and matching 2x12 cab for 5 years or so. Every so often I pickup problems with the volume dropping out intermittently and there seems to be a funny scratching sound comming from the amp. I've had the amp serviced,re-tubed and biased(what does that mean anyway??) a few times since I've had it but the service guys can't seem to get this problem sorted. It is starting to get annoying. Can anyone reccommend a qualified service technician that will be able to help me fix this ausum amp? I stay in Cape Town.

Thanks 8)

nick

Matta (Matt Allison) on this forum does repairs, I would send him a private message if he isnt able to help you he will certainly be able to tell you who can.

AlanRatcliffe

Karel Mars is your best bet - hes just fixed up a Twin for me. He's here on the forum, so you can PM him from his profile:
http://www.guitarforum.co.za/profile/Karel Mars/

Explorerlover

Stupid question, but are you sure your cables are allright? I picked up the same thing with my DSL. The cables were the suspects.Exactly why I don't know, but it seemed to be the case.

Skywalker

Wicked! Thanks guys.

Cables all good. Must be something up with the amp i think. I'll check over them again just to make sure.

AlanRatcliffe

BTW, sounds like a dry joint, iffy switch on a send or return jack or a faulty pot. But these things can be difficult to track down.

Have you tried turning pots when the problem surfaces and/or inserting a cable into the loop?

Skywalker

Havent tried that yet Alan. Will give it a go-maybe make it easier for a techie to sort it out quicker.

Thanks.

AlanRatcliffe

Skywalker wrote: Will give it a go-maybe make it easier for a techie to sort it out quicker.

You'd think so wouldn't you? But it doesn't sound like you've had much luck with techs so far...

matta

Alan Ratcliffe wrote: Karel Mars is your best bet - hes just fixed up a Twin for me. He's here on the forum, so you can PM him from his profile:
http://www.guitarforum.co.za/profile/Karel Mars/

Karel is the local amp guru. As Nick shared I do tech work as well but mainly solidstate, Karel is the valve/tube guru.

RE techs, sadly most don't really care... sorry to say it, but there IS a shortage of techs who REALLY love their job rather than it being a job. Most are qualified EE's (Electrical Engineers) NOT musicians at heart who make a living teching. Often the simple tonal things slip by them, subing any old caps/valves and it is 'fix it in the mix' situation.

I've had the amp serviced,re-tubed and biased(what does that mean anyway??

Well part of the service sounds like it was re tubed and then biased... most amps require you to rebias them after each set of tubes (some amps are cathode biased so they are normally fine as long as you have a MATCHED pair or quad's on the output section, though if the amp is very old the fixed bias resistors need to be checked to see they are still in spec). Preamp valves are also biased via a fixed resistor and very rarely need to be rebiased.

Biasing is done because the when you change tubes you will find that in most cases the current/voltage on them changes and each tube type has an 'optimal' range to work effectively, running them too 'hot' decreases the life of the tubes and impacts on other parts of the circuit, causing it to work harder which can lead to damage being done to other components.

Hope that makes sense, trying to simplify it into laymans terms.

Cheers

Matt

Skywalker

Ausum! Thanks guys.

Yeah I've had a few probs with a few local guys the last few years - I'll spare you all the details.

I will most definately get in touch with Karel asap. Sounds like the special trip I will have to make to Paarl will be worthwhile.

Rocking forum BTW and thanks again for the help. 8)

Karel-Mars

Hi Skywalker

I worked on a JCM2000 recently, and ultimately got it running smoothly. There is a few issues with the JCM2000.

Check here http://www.lynx.bc.ca/~jc/TSL122.html

Main thing is, some boards have the wrong resistors on them, and they change their value when getting hot. This makes the amp prone to erratic behaviour.

FenderBender

matta wrote: there IS a shortage of techs who REALLY love their job rather than it being a job. Most are qualified EE's (Electrical Engineers) NOT musicians at heart who make a living teching. Often the simple tonal things slip by them, subing any old caps/valves and it is 'fix it in the mix' situation.

I have to agree with you Matt. In my experience, the primary reason for techs becoming disgruntled or NAFI is that most tech staff are abused by management. This is mainly due to superiors not understanding the time, resources and cost required when working with complex or intricate technical projects.

I decided never to return to the corporate world or work for a boss after receiving harsh treatment from the company I worked for during the start of the credit crunch last year. I started playing around with guitars and really enjoyed as I learned. I am more tech than guitarist, although playing a guitar and being a forum member helps me balance hard electronics with the much needed musical awareness that is required by someone that primarily serves musicians in a technical capacity.

Well it has been a slow start, especially in this economic climate we are faced with, but I have a few loyal supporters and things are starting to move along smoothly. I have not earned a salary for nine months and cash flow problems can cause stress at times, but the prize of no longer having to own two cars, buy smart clothes that can only be used for work, get up at ungodly hours to make it to work on time, sit in traffic for three hours a day or answer to an idiot make the lean times bearable ?