Question about SWR WorkingPro 15 200 Watt 1x15" Bass Combo Amp

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SWR WorkingPro 400 watt head - no sound, Preamp Clip red LED is continually lit, Limiter green LED continually lit - fuse is perfect. It worked for a few minutes, then just stopped.

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  • greg_apel450 May 31, 2010


    The Preamp Clip red LED is continually lit. No instrument cables are plugged in.

    When I do plug in an instrument cable, nothing happens. Mute button does nothing, and the limiter light is continually lit...cannot turn off the limiter.

  • greg_apel450 May 31, 2010

    I sent a drum machine signal through the effects return, and nothing is getting to the cabinet through the power section. I made sure the drum machine signal was pretty high...and the gain & master were up high enough, as well as the effects blend.

    I hear what I can only describe as a low volume 60Hz hum coming through the cab...and some light fuzz mixed in....and that's with or without a signal in the effects return.

    I did try running the drum machine (Boss DR-770) signal into the main input...and with the DR volume up halfway, I can hear a little bit coming through the cabinet...but it's very low volume, fuzzy, and decayed. So, it seems that without the effects loop (send or return), the signal is making it to the power stage, but very little is getting through. And, the signal has to be active and pretty high to even get a peep out of the cabinet.



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Since the PA clip is not lit, the problem seems to be up front...

First thing is to look for a bad cable as a broken ground could be putting hum at a clipping level. First thing, test this by unplugging all inputs. If the clipping light goes out, then you have bad cables or a ground loop.

Try sending a line level signal into "Effects return" to test if the power amps are OK.

If the clip light is still on, turn all gain controls down to minimum. If light is still on then take unit for servicing.

Posted on May 31, 2010

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  • Fred Yearian May 31, 2010

    If you can somehow send a signal into the effects RETURN line to see if main amps are OK that is an important test. If no signal will go through there, then I suspect a part of the power supply is defective.

    usually the amps will have plus and minus 15 volts for the preamps and often plus and minus 40 to 90 volts for the power section. For the effects section if digital a plus 5 is common.

    When one or more of these voltages are not present, often the indicators such as clip and limit freeze on or off.

    I think your unit needs to visit an electronics shop either your own or a suitable repair facility. I wish I had a schematic for the unit as I could probably point to further tests that you could do... testing the power amp by sending a line level signal in is important part of troubleshooting this problem.

  • Fred Yearian May 31, 2010

    With that test it is likely there is a failure in the power amp portion that has taken down the power supply as well.

    The unit will definetly need service and will likely have several blown parts.

    To avoid things like this make sure speaker leads never come loose and are in place before powering these units, not that this was caused by a problem of this, this time.

    If you are electronically adept you could open the unit and look for blown parts, although not all bad ones will show signs of damage.

    A trick I use when re-powering a repaired amp is to put a light bulb like 100 to 150 Watts in series with one side of the power cord.

    Since MANY of these amps use switching power supplies that run off of rectified raw line power, one should always use an ISOLATION transformer for safety when working on these.

    I have not been able to find a schematic of this unit yet.

  • Fred Yearian May 31, 2010

    I found a better schematic. The MOST likely cause of the clip and limit lamps being stuck on is loss of the -15 volt power supply.

    Check R2 isn't open, D6 is not open (not likely) and that D4 and D5 each have around 7.5 volts across them. Check that C6 is not shorted. Last three are strongest suspects.

    A short in one of the IC's that are fed from the -15 can cause problem... Search these with the "finger test" looking for a hot chip.



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SOURCE: SWR WorkingPro 400 watt head - no sound

I have found a site with SWR schematics: They have one for the SM400 which may be very close to what you have, or at least parts may be the same.

Posted on May 31, 2010

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