Fire in the hole! Dean Markley CD60

[Randall]

Poor bastard customer brings in his amp that he said smoke came out of a couple of days ago, and the next day was told he needs emergency open heart surgery to repair an aneurysm in his heart. I opened the amp while he was here to show him this:


Acrid black ash everywhere, especially on the ceiling of the cab right over this spot. Looks like the board burnt up real good between V5 plate and it's cathode trace, which passes by pretty closely. I haven't pulled the board yet to look at the other side, but did this board go conductive and burn out, and if so, why? Measurements to the OT are 152 ohms from red to brown, and 83 ohms and 69 ohms from center to either side, so that looks good to me.

So I know some Marshalls are known for this, but I have not heard of DM's doing it. And what is the fix? Removing all the carbonized and soldering in a decent insulated piece of wire to bypass the trace where it passes so closely to that lug that connects B+ to pin 3 of V5? The other side takes a different route for the cathode, so it seems not an issue over there?

This is the same amp I mentioned 6 months ago that the OT brown and blue wires were reversed, FWIW.

I'm not seeing a schematic for this one anywhere so far. It's not a vintage one, it's the newer one with digital reverb.

[MarkusBass]

And what is the fix? Removing all the carbonized and soldering in a decent insulated piece of wire to bypass the trace where it passes so closely to that lug that connects B+ to pin 3 of V5?

Yes, removing all the carbonized and soldering in a decent insulated piece of wire to bypass the trace sounds good. Make sure that the output tube is not shorted.
Isn't it a reissue of an amp from 80s? Here is schematic of a slightly different model: http://music-electronics-forum.com/t39900/

Mark

[Enzo]

An arc formed, the arc was what burnt things up. The black stains are soot from the flare. A Qtip and some alcohol will clean a lot of the soot off, leaving a true idea of what is actually burnt. All carbonized board must be ground away.

[R.G.]

+ a bunch to the charred board needing to be removed back to clean, un-affected margins.

At one time I worked on systems with supplies that ran several hundred amps of low-voltage DC to a nest of logic boards. The low voltage DC made it harder for board charring to start, but if it did ever start, the charred board epoxy decomposing to carbonaceous soot would become conductive, and that would then conduct the high current supply enough for the PCB material itself to go into thermal runaway and keep on eating away at the board as long as the power supply was on. The condition was referred to, naturally, as PCB cancer. in tube amps the runaway is less likely, but the charred paths will wreak havoc with signal paths.

The charred stuff has to be cut away.

[Randall]

As I ponder this situation, it occurs to me that I will likely lose the lug next to pin 3. Not seeing a good way to attach the OT wire on that socket.

[Randall]

Ok, so another angle here. Assuming I remove the charred board and figure how to resolder the OT to pin three. Assuming little or no other parts involved, what would consensus be on what to charge for this job? 2 -3 hrs estimate? It's not a small repair.

[Enzo]

Don't you have an hourly rate? Mine was $60. Two hours was $120, not unreasonable for an amp that went up in flames.

[Leo_Gnardo]

Don't you have an hourly rate? Mine was $60. Two hours was $120, not unreasonable for an amp that went up in flames.

Think about those air conditioning bills you'll be having to pay soon Randall. Gotta bring in some cashburgers to keep the biz going!

[Enzo]

You are not being fair to yourself if you think in terms of what you might want to pay, it is about what your service is WORTH. Included in your labor time is your accumulated experience, your ability to actually fix it without making it worse, it includes having a facility in which to do teh work, and a stock of parts or resources for part that you need for the work. And so on, it is all part of the bill and worth more than the $10 you wish it cost.

people bring me amps and I found over the years, most of them expect the bill is going to be $150 or more, when most times it is under $100, plus any tubes it needs.