Help with JCM 800 2203x

[lespaulplayer]

I am having a static like hum problem with my JCM 800 2203 reissue. It all seemed to start after I blew a power tube. When the power tube blew it took out the HT fuse with it. I replaced the fuse and put new tubes in the amp. Biased it up and noticed the static like hum. Thought maybe it was a tube issue. I tried replacing the pre amp and power tubes one by one to see if it resolved the issue. It didn't.

The hum is there even when nothing is plugged into the input of the amp. Is it possible that my OT is taking a shit or got damaged from when I blew a tube? I'm just trying to figure out where this hum is coming from? I checked everything over on the inside and everything looks normal. Not sure what to do.

If something needs replaced, I'm not an amp tech by any means and do not plan on doing the work myself. I'm just trying to figure out what is wrong with my amp. I am capable of checking simple things that don't involve me poking around inside too much. I do know what you are not supposed to touch in an amp. And I am familiar with how to drain power caps, but I have never done it myself. I've only read how to do it. I would eventually like to learn how to do repairs and get into amp building, but I'm not going to lie to you and say that I have that knowledge right now. So I would appreciate any help that anyone can give me. Thanks.

[Firestorm]

I think you've done everything you can do without being more adept at troubleshooting. When the tube shorted, it might have taken out a screen resistor. Or damaged the bias supply. Or arced a carbon track on the tube socket. Or (hopefully not) shorted a few windings on the OT. Find a reputable tech and tell him or her what happened. That's the shortest distance to getting it fixed.

[selloutrr]

are the filter capacitors original?

I had a fender bandmaster come in a while back with the same symptoms due to the age of the amp I recommended a cap job.

Going back over my notes:
Tested the PT and OT
Replaced the Electrolytic Capacitors,
Power section resistors,
New Matched Power tubes - Customer supplied,
Matched sides Phase Inverter Tube - Customers Request,
Cleaned the Tube Sockets,
Replaced Old Screen Resistors with New matched set,
New Fuse,
Tightened all Grounds and Loose Bolts,
Lubrictated / Cleaned Pots,
Biased New Tubes

Not sure this helps but it did fix the problem, If the filter caps were old they could have taken a hit.
If you are set up to work on amps you can test the OT for Shorts, though it is dangerious and not recommended.

[lespaulplayer]

are the filter capacitors original?

I had a fender bandmaster come in a while back with the same symptoms due to the age of the amp I recommended a cap job.

Going back over my notes:
Tested the PT and OT
Replaced the Electrolytic Capacitors,
Power section resistors,
New Matched Power tubes - Customer supplied,
Matched sides Phase Inverter Tube - Customers Request,
Cleaned the Tube Sockets,
Replaced Old Screen Resistors with New matched set,
New Fuse,
Tightened all Grounds and Loose Bolts,
Lubrictated / Cleaned Pots,
Biased New Tubes

Not sure this helps but it did fix the problem, If the filter caps were old they could have taken a hit.
If you are set up to work on amps you can test the OT for Shorts, though it is dangerious and not recommended.

yes the filter caps are original, but the amp is a 2005, so that is pretty new. Do you think the caps could go bad that quick on a 2005? And I'm not familiar enough to work on an amp. I do know what all the components are, but I just don't have the knowledge or experience to be replacing stuff on my own yet. I did find a place online that is somewhat close to me. It's a 2 1/2 hour drive, but I don;t know where else I could take it. Do you think this place looks reputable? Have any of you guys on here heard of this place? I just don;t want to take my amp to a parts replacer that doens't know what their doing. Here is the link.

http://mathes-amps.com/services.html

Thanks for your patience with my limited knowledge, and your help so far everyone.

[selloutrr]

Since the Amp is rather new (2005) I would go to Marshall USA and search for a Marshall Authorized Repair Center in your area. If you can't find one, contact Korg they are the USA distributor for Marshall.

IMHO The new (2000 or Newer) Marshall amps Sound great but the build quality is sketchy, and the amps are difficult to work on to put it nicely.

The link to the repair tech, looks to me as more of a Fender specialized builder then a current production PCB Marshall tech.

I've been in about 20 of the new Marshalls and turned away 100+. I recommend sending them to a Certified Marshall Service Center because it's cheaper then paying my hourly rate to trouble shoot. The Marshall Tech's have access to field notes and technical support as well as factory parts at a discounted rate. I'm not 100% but it's possible they offer a flat rate repair.

[Firestorm]

Unfortunately, Marshall dumped Korg late last year and the new USA business seems yet to have developed an authorized repair network.

[Structo]

Really?

Wow, bad Marshall, bad.

[selloutrr]

They are probably having a hard time getting people / centers to work on the amps for what they are willing to pay. I would loose $ doing repairs at a flat $75 on a new marshall. Even if they sent me a high volume of repairs I loose money each amp counting break down, troubleshooting, repair, assembly, and testing would take 2.5hrs+ on a good days. then you factor in parts, Lots of full board replacements, cause it's quicker then trouble shooting or breaking out the rework station. Newer PCB Marshall's esp JCM2000's have issues with the PCB traces being to close together and arching.

IMHO I'd contact marshall direct and give them and ear full about the service issues and build quality of the new amps, based on what they charge and the "reputation" Marshall stands for, they need to get it together and provide customer service.... But ask nicely first

[selloutrr]

FYI -

To become a Marshall Repair Center all you need is

1.) a Store front - to advertise Marshall
2.) an address to ship to
3.) the ability to repair PCB and Solid state devices

[lespaulplayer]

Yeah that was dumb on Marshall's part. Well, I shot that mathes amplification an email, we'll see what he says. It sucks living where I live, because there just isn't too many options for me on where I can take it to get it fixed.

[lespaulplayer]

They are probably having a hard time getting people / centers to work on the amps for what they are willing to pay. I would loose $ doing repairs at a flat $75 on a new marshall. Even if they sent me a high volume of repairs I loose money each amp counting break down, troubleshooting, repair, assembly, and testing would take 2.5hrs+ on a good days. then you factor in parts, Lots of full board replacements, cause it's quicker then trouble shooting or breaking out the rework station. Newer PCB Marshall's esp JCM2000's have issues with the PCB traces being to close together and arching.

IMHO I'd contact marshall direct and give them and ear full about the service issues and build quality of the new amps, based on what they charge and the "reputation" Marshall stands for, they need to get it together and provide customer service.... But ask nicely first

The JCm 800 reissues are built nothing like the JCM 2000's. The 800's are built just like they were back in the 80's. None of the tube sockets are connected directly to the PCB like they are on the JCM 2000's.

[lespaulplayer]

I don't want someone who is going to just start hacking my board apart and start replacing parts if they don't need it. I told that Mathes amps that in my email, I just want to find out exactly what the problem is, and just get that fixed. I don't want anything else in the amp changed out if it doesn't need it. This is what sucks, because if I had the knowledge to do this myself, I would take the steps to do it right. I'm worried that someone is going to hack my amp up. I mean I could drain the caps and start replacing stuff too, but I want to take it to someone who knows what they're doing, so that isn't necessary. I mean, that is what I'm paying for is the persons knowledge and experience, right? I'm just saying I could be a parts replacer too. I just want to find out exactly what is wrong and get that fixed. Not hack my board up. Nothing else.

[Firestorm]

It doesn't say anything about his diagnostic chops, but for what it's worth Mathes' own amp builds look first rate. What part of Iowa are you in? I've run across a few other names out there.

[lespaulplayer]

It doesn't say anything about his diagnostic chops, but for what it's worth Mathes' own amp builds look first rate. What part of Iowa are you in? I've run across a few other names out there.

I thought his amp builds looked good too. . Lincoln is probably like a 2 1/2 hour drive for me. I live in north west Iowa. I'm about an hour east of Sioux City, two hours away from Omaha, or Des Moines. And places like Davenport and eastern Iowa are like 3 1/2 to 4 hour drives for me. but I would be willing to travel anywhere to get my amp fixed.

[Firestorm]

Doug Hoffman's EL34 World site lists a tech named Art Jacobson in Rock Rapids. Know nothing about him, but may be worth a call.