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Dead PA any Suggestions?

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  • #1

    Dead PA any Suggestions?

    I have a Tosh PA-8250 That is getting ready to die. We were all practicing when smelled a burning odor coming form the PA. It was still working except we got a strange noise like phasing white noise. it still amplified and never turned off just smoke smell and noise. I have scoured the Edges of the internet looking for the schematics but they are no where to be found.
    Any suggestions on what it may be? Id love to rip it open and fix it but without the schematics Im just replacing failed components in the dark.

    Thanks
    Tags: None
  • #2
    The first order in any repair is visual inspection. You have smoke an smell. Can you identify what burnt. Post a picture. See if someone spilled a drink in it. Check for domed filter caps.

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    • #3
      Originally posted by olddawg View Post
      The first order in any repair is visual inspection. You have smoke an smell. Can you identify what burnt. Post a picture. See if someone spilled a drink in it. Check for domed filter caps.
      True, very true, but sadly with out the schematics I can only replace any failed components, I cant verify or test the circuitry, There has to be a reason that what ever part failed. I've never been lucky enough to have a single component fail usually something up the chain causes my failure. I dont even want to crack the amp open until I can look at the schematics. I cant believe that schematic heaven is no more. Though I doubt they have this mystery PA.

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      • #4
        Several years ago this was their contact:

        Tosh Electronics Corp
        Bowling Green, OH

        419-353-1381

        How about calling some electronic company in their neighbourhood as ask about Tosh?
        In the worst case a power amp can be fixed without schematic - this is what many guys here are doing.

        Edit: Olddawg didn't tell you to replace the failed component. He told you to find the part with visible signs of heat and post a picture here. You may not know what other parts had failed, but the guys here may know, or at least guide you how to find them.
        You may also specify your location (I assume this in the States) and someone may get it fixed for you. It's because you say that you may fix the PA with the schematic only, and you cannot find the schematic. Isn't the conclusion that you cannot fix the amp on your own? Someone else has to do it.

        Mark
        Last edited by MarkusBass; 11-14-2012, 10:17 PM.

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        • #5
          Originally posted by MarkusBass View Post
          Several years ago this was their contact:

          Tosh Electronics Corp
          Bowling Green, OH

          419-353-1381

          How about calling some electronic company in their neighbourhood as ask about Tosh?
          In the worst case a power amp can be fixed without schematic - this is what many guys here are doing.

          Mark
          Tosh was the owner of DeArmond pickups back in the 80s, I think. I don't think that they have been around for some time now.

          Mark is right, the amp should be fixable even without a schematic. There aren't that many ways to build an amp that, so it will probably be very similar in design to some other brand product, like a Peavey or a Kustom, etc. Otherwise it's just a boat anchor.

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          • #6
            Tosh was a real low-rent amp operation that is long gone. Yess, the circuits are real basic and similar to old Peavey designs.

            Without a schematic, I look for certain things. First, identify what was getting hot. You could have a failing zener diode in the power supply for the mixer section, and don't need to even think about the power amp.

            But if the power amp needs help, we still check its power supply voltages, we check for any DC offset on the output. If parts have failed, we check all the power transistors, and look of any open resisors associated with them.

            We may not have a schematic, but all the same elements are in most of them.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              What Enzo said. Or you could Tosh it in the Trass...

              (sorry, I just couldn't resist )

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              • #8
                Since it was still working my guess is a power supply problem. See if you can see what is smoking. It may simply be a Zener or a regulator IC failing. If it is a stereo amp and you have a problem with one side power amp, the other side is your schematic. If the problem is a preamp channel failure, the other channels are your schematic. You can find your preamp rails by looking at a spec sheet for an IC. It will probably be +/- 12,15, or 24 volts with higher voltage rails for the power amp(s). Shouldn't be that difficult to figure out. It's basically worthless. Open it up and look. Bench techs repair stuff without schematics all of the time. What have you got to lose. Just don't hurt yourself if you don't have the basic skills to safely work on it.

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                • #9
                  Here is a picture of one for reference.

                  Tosh PA-8250 P Mixer | Electronics for Sale in Harvey IL | 3086484549 | Classifieds on Oodle Marketplace


                  Think of it as a sort of ersatz Peavey XR600, but not as fancy or refined. 250 watts mono.
                  Education is what you're left with after you have forgotten what you have learned.

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                  • #10
                    There appear to be several patch points on the front of the mixer. It would be helpful if you can isolate the fault to the mixer or power amp section using EQ or main out or amp in jacks etc. If the problem exists in the mixer and the power amp, chances are it is power supply related.
                    Originally posted by Enzo
                    I have a sign in my shop that says, "Never think up reasons not to check something."


                    ​

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                    • #11
                      I haven't cracked it open yet but I suppose I could, if its not too complex I suppose I can just test everything. Replace all Caps and just overhaul the entire thing. But then again if this thing is a hornets nets of mess and garbage, Oh well no harm done. We are already looking into a new more modern PA.

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                      • #12
                        Originally posted by morbe View Post
                        I haven't cracked it open yet but I suppose I could, if its not too complex I suppose I can just test everything. Replace all Caps and just overhaul the entire thing. But then again if this thing is a hornets nets of mess and garbage, Oh well no harm done. We are already looking into a new more modern PA.
                        It's never a good idea to start randomly replacing parts. It gets expensive, waste your time, may cause more problems, and probably will not resolve your issue. As was suggested, try to isolate where your problem is, first by visual inspection, them by isolating major circuits in the unit. Take a line out into another amp. Sounds ok? Problem is in the power amp. Run an iPod into the main amp direct. Sounds ok? Problem in the preamp. Still I would start by a visual inspection and checking the power supplies. Smoke came from something. Put your nose to it, we all do. Bright light and a magnifier too.

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