Funny smell from my mixer

C

CurtZHP

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Oct 26, 2013
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Gear owned
DM-24
Still trucking with this thing after all these years. Can't bring myself to part with it.

The last day or two I've noticed a slight odor emanating from my console when I'm leaning over it. It's not quite a burning smell, but what one might smell if electronics are running a bit too hot. I'm noticing it over all the faders to the right of channel 11. It's my understanding that the power supply is located just to the right of these, under the transport section. I've heard of the caps going bad. Am I next??

Any diagnostics I can perform to confirm this?
 
Take it apart, lift off the top and run the mixer. Check for smell and hot components. There is a shield you'll have to remove to look at the caps. Chances are they are leaking current and over heating. If you replace them now you will avoid a catastrophic failure like I had.
 
Popped the top on her. Saw a nice brown spot on the power supply shield, indicative of something running HOT. Looks to me like this thing was recapped once before.

I bought this mixer back in late 2003, and it was a factory refurb, so that would explain that. Looks like they put in 105C caps too.

None of them looked swollen or oozy. I'll replace them anyway, since caps are cheap.

Anything else I should look for?
 
Make sure there are no shorts on the current sensing transformers. The insulation could be compromised by excessive current because of the caps leaking to ground. Beware if the coils look dark.

You can check the component temp rise with it opened up and powered on. Use an infered thermometer or thermal imaging if you have it.
 
If you do not have reliable air conditioning and keep the room around 70F, always power OFF the DM24 when you are done for the day. These mixers are sensitive to overheating, and need to be kept cool or many things can potentially fail, the lcd screen, the power supply...
 
I always shut it down when I'm not using it, and the room is always cooler than the rest of the house. Already replaced the screen a couple years ago.

Pulled the power supply and removed all electrolytic caps. Ordered a whole replacement batch, which should arrive today.
 
Well, I recapped the power supply successfully. Turns out that wasn't the problem after all. The thing still smells funny. I noticed that the heat is emanating from what looks like an induction coil located amongst the caps. It's very hot to the touch after just a few minutes of power. The circuit board designates it as L3 ("L" is usually used to designate an inductor).

Here's the other problem. This power supply is different from the one shown in the Tascam service manual. At some point they must have redesigned it.

So I have no idea how to go about replacing this inductor, or even if that's the real problem. Something else downstream of it could be pulling excessive current through it. And without a proper schematic, I'm flying blind.
 
Hello,
You have arrived at the same point I did. My "L3" inductor was fried. Yours may be suffering from insulation breakdown in the coils. When I powered my supply on I could see sparking between the windings. Are the coil wires discolored? That inductor should have the same coloring as "L6" next to it.
I suspect the order of failure is; capacitor leakage from overheat > capacitor failure from thermal runaway > inductor insulation breakdown from thermal runaway > inductor shorted.
That's why I went with the TFX power supply, Caps I can replace but finding the direct replacement current sensing transformer proved difficult. I even unwound the coils in preparation of rewinding it but the TFX solution was cheaper, faster and proved to be rock solid.

You can eliminate the load by unplugging the power cables from the supply. Don't run it too long this way as some power supplies need a "minimum load" in order to regulate properly. OR you can use a current clamp to measure how much current each board is drawing.

The schematic shows two power supplies. The one with component detail is the +15, -15 & 48V audio circuit linear power supply. I could not find component level detail for the switch mode power supply. It is shown as a "block" in the interconnect schematic. The digital circuits require +3.3V, +5V, +12V & -12V just like a PC so that's the direction I went. The TFX supply has ample current and is inexpensive although more $$ than an ATX but I wanted it to fit neatly inside the chassis.
 
My supply looks just like yours pictured here in another thread:

Tascam DM-24 Power Supply fail

L3 on mine is not black, but it's definitely brown. What's odd is that the brown coating seems to be flaking off in a couple spots. Is that the insulation you refer to?
 
Yes, If it is flaking off, it has suffered over heat / thermal failure.
 
Any idea what would have caused that other than capacitor failure?

By the way, would you happen to know the model number of that Seasonic supply you installed and where you got it? I'm thinking I may have to move in that direction. Does the fan run all the time, or just when it gets hot? How noisy is the fan?
 
Hello,
Seasonic SS-350TGM 350W 80 Plus Gold TFX12V v2.31 Power Supply] [PS-SS350TM]

I got mine from Superbiiz, probably not the best price but Fry's our local electronics store only had 300W version (much cheaper) but there was a concern it may not have enough +5V current for the DM24. So I went with the 350W for a bit more money. During testing the fan never came on while I was using it. The instructions said that if the current draw was less than 50% of the rated capacity the fan may not rotate. that suggests that the 300W supply may be enough but then the fan may run. I suspect it will run on hot days but it is supposed to be only 29 decibels which may not be too bad inside the chassis. It may help cool the display too.
 
As far as powering the Seasonic supply: Did you just connect its IEC power input parallel to the console's own IEC input?

Aside from rigging the outputs of the supply to the various mulitpin connectors, any other landmines to look out for?
 
Hello,
Make a cardboard box the size of it first and make sure it fits in the space you have in the chassis before you order.
There are circuit boards fitted to the top panel that crowd it from the side and the top.
 
Good idea. Basically what I did was measure the existing supply and compare the dimensions to the replacement. But I did this with the top off the mixer, so I should confirm that.

Thanks for your help!
 
Hello,
That supply looks like it has a small fan that may be noisy when running. Oh I don't for sure it was just a thought. It may fit much better than the one I used.
 
Well, if it's anything like the supply you used, and you said yours hardly ever comes on, maybe it doesn't even need the fan.
 
Since the original PS over heated it probably could have used one. :)
 
Well, I'll see how noisy it is, and if it's an issue, I'll just remove it and find a quieter fan to mount next to the unit.
 
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