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Carvin DCM150 power amp overheating

Discussion in 'Vintage Analog Gear' started by flagos, Dec 24, 2011.

  1. flagos

    flagos Active Member

    Hi:

    I found out there an old Carvin DCM150 power amp. I tried it and I was surprised how good its sound is! But the heat that the unit reaches, surprised me also!

    Anyone out there remember/know something about this units concerning heat?

    Thanks in advance!!!
     
  2. dvdhawk

    dvdhawk Well-Known Member

    Are you sure the "Bridge" button is in the correct position? And that your impedances are 4-ohms or more to each channel?
     
  3. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Also, can't hurt to pop the top and look around in there. That's the FIRST thing I do with used equipment.

    Anything look like it's getting toasty in there? Look at all the components to see if they look they've been getting too hot, and look at the board to see if anything looks a bit "browner" from heat than the rest of the board. Those are clues, and can help narrow down if anything is cooking. Are the vent holes blocked by dirt or giant dust-bunnies?

    Also, never know how must dirt or funk is caked inside something until you open it up. A few years ago, a guy up and gave me a Ramsa power amp, claiming something was wrong with it, and they bought another amp and didn't need it. He said HE bought it from a closed Mexican restaurant (you can see where this is going...)

    I opened it up and it was CAKED with taco-shell-smelling reddish-brown waxy grease. You could literally not read a number on anything, or tell a resistor from a diode. It was all just reddish-brown gunk!

    Apart it came. Into the dishwasher. Good blow dry with a heat gun on low, after. DeOxit clean and lube afterward in the pots and jacks. Let it sit a couple of days, just to make sure no moisture was under things, still.

    Put it together, and it's worked perfectly since.

    Anyway, is that a fanless amp? Fanless amps can get a bit warm. The heat sinks are the only thing drawing a lot of heat from those hot output transistors. The amp may just normally feel fairly warm, even if it's perfect. Are you sure you're not confusing "normal" warm with actually "pretty freakin' hot!"?

    Kapt.Krunch
     
  4. flagos

    flagos Active Member

    Thanks for the answers!

    Dvdhawk: yes, the bridge is off and the skpeakers impedance is 4ohm.

    Kapt.Krunch: I inspected the device and looks good to me.


    I forgot the mention that I'm in Argentina so I need an auto-transformer (220v-110v) in order to run the device. I suspect that is the problem. Today I run it with the cover off and I noticed that the fuse is red-lighted! And if I continue using it, the fuse will blow after 15 minutes. Maybe there is a problem with the ground auto-transformer connection...

    Thanks so far guys!
     
  5. JoeH

    JoeH Well-Known Member

    I suspect your power supply/converter. Check that throroughtly first.

    If after that it's popping fuses AND running hot, but still passing sound, then there's something borderline going on, parts-wise. Seems like it's at least running ok enough to function, but getting hotter and hotter as it runs & gets up to speed?

    It's time for some detective work... How is the sound itself? Any AC hum or self-noise? Do the channels sound identical to each other? Is one side louder than the other? I think someone already asked about a fan and if it's working properly. You may also want to look for a part or circuit board that's too close to something else; perhaps a transistor casing that's touching a chassis point somewhere. (I fixed an old Scully Tape deck with this problem years ago; as soon as it got hot, one of the power supply transistors got close enough to the casing (Grounded) and would pop the circuitry. Once it cooled down, it worked again, till it came up to running heat, and then....pop! I found that one without a schematic, just good detective skills.)

    My guess is something like that, or a leaky/bad cap somewhere. If it's in the power supply, though, you might hear it as hum or poor qualitiy sound, although you say it sounds great. One thing you should probably try is to get a schematic of the amp itself, and start planning on what critical parts you may need to replace. Most of the transitors (esp the driver and output trans) should be available as generic replacements, if not original stock.

    If all else fails (and I DO NOT recommend this, although I know some "techs" have done this as a last-ditch effort - and it takes serious balls to do this), you can always raise the value of the Fuse and see what cooks/blows up.

    Again, I DO NOT recommend this, you would need a fire extinguisher handy, a flame-proof work area, and nerves of steel to attempt it, but it will eventually show you what's bad. (Seriously, I had an assistant do this - he was admittedly a little nuts, but - in a few dire, hard-core cases, he found out what part was bad, and fixed it that way - the hard way.)

    So after you've ruled everything else out, get the schematic, a good multitester, and start checking voltages before the correct fuse pops. Listen to either side sonicaly, check for clues that way. Swap out parts as much as you can before it pops the fuse each time, maybe you'll find it that way....

    Keep us posted on how it goes. Good luck.
     
  6. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Here's a link to schematics (in case you don't have them). DA11

    Follow them through. Measure some stuff.

    One other thing. Are you SURE you have the switches on the back set properly? Apparently, there's a PAR (parallel) switch on the back, near the bridge and ground lift switches. The ONLY time you want that engaged (pressed in) is if you are running only a mono signal into Input 1, as this will feed it to both channels. (Like a "Y" cable.) It parallels that signal to Input 2, which you can use to send on to another amp's input...as in 'daisy-chaining' them. If you are using both channels' inputs, do NOT engage that switch. It shorts the two input signals.

    Dunno exactly what that would cause in the amp, but it probably wouldn't do anything good for the input device(s).


    Although the manual doesn't mention it, it's highly unlikely that you'll want the "PAR" switch engaged while in "Bridge mode", either...which you are apparently not using.

    Anyway, just make sure those switches are set correctly for your application.

    Kapt.Krunch
     
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