Marshall JCM2000-60W: Serious damage from whiskey spill!

[foamyoasis]

I have a Marshall JCM2000-60W amp that had whiskey spilled in it during a gig with the previous owner. If nothing else, the photos of the damage might be interesting to the readers. I have been working very intermittently on this amp for a couple of years but am ready to give it another shot. Thanks in advance for any advice!

I have very little experience working on tube amps, and I am wondering if anyone has some suggestions on where to go with this repair. I'm concerned that the damage could have been more extensive than is visible, but someone else (more experienced than me) told me he didn't think so.

The visible damage is pretty limited to the area in and around the big electrolytic capacitors. Basically, I have rewired all the burnt out traces properly (to the best of my knowledge!). I replaced R26, 260 Ohms, as it read infinite resistance.

I'm just getting back into this but the only measurement I can remember is that ZD3 on the VBIAS circuit read zero volts (I'll have to confirm that).

I started the amp with variac slowly initially, but it seems to power up without any serious consequences, but there is absolutely no sound/noise in the speakers at any point. The two large tubes glow and the four small tubes have just a tad of very faint glow.

enjoy!

[J M Fahey]

*Maybe* it will be better to discard that board entirely, salvage the chassis, cabinet and transformers and build there a point to point wired (on turret or eyelet board ) classic Marshall, say a Plexi or JCM800.
There are even boards available on the market which are pre-built or come in kit form. Google Hoffmann, Ceriatone, etc. or "marshall turret eyelet board kit"
You will still need to make the socket holes.
It will sound *much* better.
These kits require less deep electronics knowledge, they are accompanied by very clear layout and wiring images, search around.
You already have the most expensive parts.
Just my 8 Peso cents, worth about 2 US cents.

[R.G.]

+1 - can it, rebuild something into it if necessary.

From the technical viewpoint, once circuit board material starts decomposing under heat, it forms carbonaceous, well, call it charcoal. The charcoal is conductive and resistive, supports combustion, and will continue to smoulder if fed by enough current and voltage. I have seen high current power supply boards where the PCB itself charred in a kind of glowing electronic cancer which spread outwards. The cure for this, if it is one, is to completely cut out all the charred PCB material, then see if there is enough to save. Frankly, what remains is often best dropped in the dumpster. Even if repaired, it will never be reliable because of the degree of surgery that was required. It may make an OK bedroom amp for a beginner who does not lose a job if his amp fails.

[Chuck H]

Sage and practical advice so far. +++ on using the chassis and trannies for a new project. For the cost of a faceplate, some tube sockets and the components you can have almost any Marshall you want with no PCB damage to babysit again and again.

[foamyoasis]

Thank you all for your advice and information. I started looking at kits, and what it looks like is that you are suggesting is building a simpler but better sounding and more practical amp, without all the features of the current JCM2000. That sound like a very interesting idea. I can't invest in the kit right away so I might tinker with the current board a bit anyhow while I learn more about amps and which one to build. I have a good deal of electronics experience and knowledge, but I have a lot to learn about guitar amps. I thought this was probably a pretty good amp and might not be too hard to repair unless all the integrated circuits and various other components are blown, but I see it might not be worth it. I will let you know if I find out anything interesting!

[J M Fahey]

If you let me say so, I always suggest everybody who's repairing something to pamper the board, to use a good solder sucker, don't wiggle parts when pulling legs (that's what unglues pads), even use solder wick to absolutely clean the pads or even, on resistors and such, to cut the legs leaving a stump and soldering the new part to them, all to keep the board healthy, because "the amp is the board", all other parts can be bought over the counter.
In your case, of course, the board is unusable and the "JCM2000" is dead, yet it can be recycled into another (better?) Marshall.
You can start by buying the empty board and plan where and how to mount it in your chassis.
Later you should get either a couple of socket punches or "cup" saws.
All other parts are relatively cheap.
Good luck.

[jrfrond]

I have a Marshall JCM2000-60W amp that had whiskey spilled in it during a gig with the previous owner.....but am ready to give it another shot.

Wasn't the first shot enough???

Sorry, someone had to say it!

Good advice here. Char-broiled PCB boards are a dicey repair on anything that handles a lot of power. The conductivity of carbonized circuit boards, tube sockets, etc. is well-documented and can cause more latent problems than you've ever imagined.

If the carbonizing is localized, it can be cut out with a Dremel tool and a piece of blank PCB material can be inlaid and epoxied in to provide a base for components and trace repair, but unless you have experience with this, it's the equivalent of microsurgery.

[J M Fahey]

Speaking theoretically, because you are not going to do it, a new board *can* be made, and might be the ultimate clone.
I personally know people who cloned US equipment, (we are talking late 70's, early 80's here, no scanners, PCs, Laser printers, etc.).
They "cleaned" the boards, free from components, wires, etc, cleaned carefully every pad and hole, and took an X-Ray of it.
You have a perfect reproduction of the copper traces, no board, no labelling, no solder mask, nothing.
From it it's easy to make a Litho Film master to reproduce the (single face) boards, either by photochemical or silkscreen process.
A friend of mine made a zillion Phase 90's clones .
He's a great guitar player, only knows how to solder, knows no electronics.
He did go to an electronics shop with all parts in a shoe box and ask "gimme these thingies".
The Hammond boxes were cloned too, (sandcasted), although were rough in the inside and with thicker walls, they weighed almost twice the original.
So now you know, if it pay$$$ (not this case), many things can be done.