JCM 2000 how much labor?

[Randall]

JCM 2000 DSL-100 in for a melt down event when the customer played thru a Power Brake hooked up wrong. Mains fuse blew, but also melted some of the fuse holder (don't know why). Customer said amp was real hot and he smelled a burning smell. The JJ EL34s paint is brown and almost gone.

Nothing on the board looks like it smoked, except the two 330uF 315v filter caps are bulging and leaning. I freed the board from the steel plate to gain access to the underside, did some limiter bulb testing, worked on getting the dead fuse out of the partially charred fuse holder, measured all four output tubes and found one was pulling way too much current (53mA) and one was quite week (19mA).

Tomorrow I intend to call the customer with a quote for a set of tubes, two filter caps and a fuse. Problem is, I can't decide how much labor to charge him. I already have over an hour diagnosing it, carefully looking for whatever else may have been an issue after what the amp went through, and It will be almost another hour installing and biasing, replacing the filter caps, and putting it all back together. But I second guess myself all the time and think, two hours to replace four tubes and two filter caps? But that is how long I will have into this when I'm done, even more if I count looking for and at schematics, trying to balance the original tubes, finding the recommended biasing procedure from the back connector (90mV/side), spending time educating the customer on how to connect the Power Brake, etc.

So what do you think? Is two hours too much for this job? My rate is $50/hr btw.

[The Dude]

Absolutely not too much! I don't charge for my own "education" if I don't know how to do something. But in this case, the amp required thorough inspection to assess damage. It wasn't just routine maintenance. Sure, you just put in some tubes and caps, but there was more to it in this case because of the cause of the failure.

[Leo_Gnardo]

Sure, you just put in some tubes and caps, but there was more to it in this case because of the cause of the failure.

Definitely! Melted fuse holder, that's some slow blow fuse. On these dreaded 2000s' you have to be thorough, as you are doing, what with that bias adjust dongle-board and other PIA features. Also, what's the manufacturing date on this one? Ones made before 2005 have a bias drift problem built in, and if the one you're working on is one of these you may want to address that before setting it loose on the concert stage or studio.

FWIW I find bias test point 70 mV to be plenty. Why Marshall insists on 90 mV - 45 milliamps per EL34 - well I just disagree. If you feel like it put in some 1% 1 ohm current sense resistors. Marshall uses 10% parts, so you could have a 20% disparity and that's supposed to be OK because the cheap ass resistors are "in spec"??? It's hard enough to check low value resistors for accuracy, not too many folks have a milliohm meter handy.

[Enzo]

I read you as replacing the fuse but not the holder???? If you had to pry the old fuse out, that holder is ruined, and it is false economy to save $2 by leaving it in there.

I never charged for my education either. But this sounds like simply a bunch of work, not you learning something new. Charge for it. remind teh customer this is not a simple failure, this is the result of abuse. You want to use a kinder word, be my guest, but abuse it is. The damage was so extensive due to their actions, not just amp failure.

If I gave you an amp and said replace four tubes and these two filter caps, you could no doubt do it in no time. But you didn't just replace four tubes and two capsd. Those were the PARTS you replaced in doing all the rest of the work.

If you go to the doctor, and he has you do an MRI an bunch of lab blood work, and he winds up prescribing a jar of pills, you don;t say, gee, that doctor bill is a lot just for prescribing some pills.

[gbono]

https://reverb.com/price-guide/guide/3760 looks like JCM DSL 2000 are in the $500-600 price range these days - I would guess the owner would spring for at least 2 hours labor considering the amps condition.

[Randall]

Well, now that I learn of the bias drift that this model is known for, which seems to me is likely what happened here, and the Dr Tube stable bias mod for $70 plus more labor, the bill is now $300. I asked him to read up on the bias drift issue before calling me back to discuss.

[Leo_Gnardo]

Read ye here about how our friends in Deutschland have gone about fixing the (in)famous bias drift problem. I've done it in about a dozen JCM2000's. Note it's also a good idea to replace the 220K grid stopper resistors (what was Marshall thinking?) with 5K6 carbon comps like they have in just about all their other amps. You may be able to skip shelling out $70 for a kit, just a fraction of that for appropriate parts.

The Marshall TSL122 TSL100 thermal bias drift repair page

The comment has been made that if this was a car, there would be a manufacturer's recall on it, no cost repair for the car owner whether original or not.

[gbono]

Never had to modify the main board in a TSL/DSL for the failure of the PCB material that causes the grid to "float" to plate voltage. The hollow drill looks like something that would be worth having unless you use a dremel tool. Dr Tube charges 125 euro on top of the price of the kit and you still need to use a dremel or buy the hollow drill.

[Randall]

Why does he refer to pin 5 as the offending pin when it sure looks like pin 7 to me. Confusing.

edit: never mind, I see why. Pin one is not where I assumed it was looking from the bottom.

Do you see any problem replacing the 220K with 5.1K or 6.8K ohm instead of 5.6K?

[Leo_Gnardo]

Do you see any problem replacing the 220K with 5.1K or 6.8K ohm instead of 5.6K?

I'm sure either will do fine.

The hollow drill looks like something that would be worth having unless you use a dremel tool. Dr Tube charges 125 euro on top of the price of the kit and you still need to use a dremel or buy the hollow drill.

First couple of times I did this, used a dremel and considered it a safety hazard. Tried a couple different bits, each one would bounce erratically when it came in contact with the tube socket pin metal. Since then, I remove the sockets, drill thru the board at pin 5 then clean up & de-burr the hole with the dremel. Then resolder the sockets & get on with the rest. Hollow drill? Mmmm I like that, can you suggest where to find 'em?

One thing makes it worthwhile, these amps do sound good to me when working, good versatility with the 3 preamps.

[Jazz P Bass]

Replace the board while they are available.

Whatsoever is wrong with that pcb material, it can only get worse.

My 2 pence.

[Randall]

Hollow drill? Mmmm I like that, can you suggest where to find 'em?

I just bought one here. Ace Hardware has them online as well.

DEWALT 3/16 in. Diamond Drill Bit-DW5570 - The Home Depot

[Leo_Gnardo]

I just bought one here.

Kool beans, if this saves me having to unass those tube sockets the price will be well worth it.

Jazz P, once fixed I've never had to return to one of those 2000's. OTOH I agree replacing the board entirely is the best solution. If I owned one of these amps, and valued it enough to keep it running well into the future, I'd do that. When amp owners are confronted with the replacement board cost, plus shipment from England, plus cost of installation, they invariably choose the second best solution. Oh well.

[Jazz P Bass]

Kool beans, if this saves me having to unass those tube sockets the price will be well worth it.

Jazz P, once fixed I've never had to return to one of those 2000's. OTOH I agree replacing the board entirely is the best solution. If I owned one of these amps, and valued it enough to keep it running well into the future, I'd do that. When amp owners are confronted with the replacement board cost, plus shipment from England, plus cost of installation, they invariably choose the second best solution. Oh well.

Yeah, I have done a few.

With one exception, it went well.

The exception had an increasingly louder hum when the amp was on over one hour.
It wasn't That loud but I saw it happening.
The owner simply turns the amp off at break.

Still, that one gave me a bad feeling.
Thereafter I recommend board replacement.

[Leo_Gnardo]

The exception had an increasingly louder hum when the amp was on over one hour.

I've had a couple that did the same. After double & triple checking that it wasn't creeping bias syndrome returning, I started to suspect filament balance resistors were warming up & drifting values, also found power transformer mounting bolts loose causing the chassis itself to hum. Quik-connect filament tabs loosening up. Just a barrel of laffs these JCM 2000's arent' they? Oh crap, one just came in... here I go to the funny farm where life is beautiful all the time. This one belongs to a store so it's "fix cheap as possible" another popular thread this week.