Did I just kill both my amps? lol

Discussion in 'The Workbench' started by JCGdes, Sep 25, 2020.

  1. JCGdes

    JCGdes New Member

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    I had a previous post with my MG102CFX amp cutting out after 5 to 10 minutes of playing. So i replaced the Fan under the heatsink and it worked greats for the last 2 or 3 weeks.

    So i bought this Zoom G5N mulit effects processor, and it was working great on the 102, for the last week or two.

    But last night the amp just cut off again. Head phone jack still works, pretty much the identical problem i had before i installed a new cooling fan. Only this time powering the amp on and off, won't bring the speakers back to life. Amp sat all night and still no sound through the speakers, but the headphone jack still works.

    Anyways after that amp cut out, I plugged my Zoom G5N into my MG30CFX, was playing along great untill the sound just went very quite and twangy sounding... head phone jack still works as normal on that amp as well....

    Not to sure what happened or did this G5N pedal destroy both my amps? lol.

    When i have time to take them both apart, i will look for cracked solder joints or any burnt marks any where i guess, but is there anything else I should be looking at here or trying to test, i can't really think of what might be wrong now?
     
  2. william vogel

    william vogel Well-Known Member

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    It sounds like the impedance is low causing the excessive heat. I don’t know what you have, if it’s all original or what. But it seems like there’s a thermal limit. If adding a fan increased the run time, it seems obvious that a thermal protection is occurring.
     
  3. JCGdes

    JCGdes New Member

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    So i took apart, the 102cfx, and just looking at the bottom side of the PCB, I found 4 possible problems?... I tried to put each problematic item in the center of each photo..

    This one appears to have a bridged connection between 2 solder points.. i don't think any solder should ever be bridged in a marshall amp? I believe this is on the board right above the heat sink, and just above the bridged solders you can see the long solders for the 2 chips on this board.

    Theres 5 contacts here, with the second not even soldered?... but the 5th solder at the end has a pin hole or cold joint near the center of the solder..

    This image shows a cylinder item with the number 8000 on it, and it has a solder job on the side with a another pinhole or cold joint..

    Than lastly heres another part of the pcb with another 5 solders lined up and the last one again has a pin hole in it...

    I am hoping this has something to do with my problem lol...

    But I am curious about that first image. why there would be a bridged soldered there? I can't imagine it bridged its self over time? so it must have come that way from the factory? so maybe its bridged for a reason.. Does it makes any sense for there to be any bridged soldered joints on a guitar amp?... Maybe this is a sign that someone was tampering with the amp already before i bought it.. hard to say..?
     
  4. JCGdes

    JCGdes New Member

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    So i took apart my MC30cfx the one that failed shortly after the 102. and i found some a couple questionable areas...


    20200925_190630[1].jpg found these 2 bridged solder joints... i grabbed a peice of solder wire folded it in half like a two prong fork so i point to them with one hand and take a pic with the other... on the other side of the board.. you will see this...

    20200925_190052[1].jpg image wouldn't upload properly so hopefully after cropping it you can still see the top of one of them capacitors looks like it was hit with an angle grinder? lol.. but there are no screws or nothing above its location, and i bought this 30cfx new from a guitar shop.. so Looks like that might be a problem with this amp, it still has sound but its very very low and quiet and dull and twangy sounding...

    But with the picture of the bad capacitor in between them you can seen a silver bar or sliver.. theres actually two of them.. and when the board is flipped over.. each end of those 2 silver bars are what are bridged soldered together on both ends... im guessing this is normal? other than that i can't find anything other bad solder joints on this 30cfx.. might just say fuck it and go buy a soldering gun tomorrow and see if i can fix the bad solder joints..

    and try ordering a new capacitor for this 30cfx. lol.
     
  5. JCGdes

    JCGdes New Member

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    @william vogel So how does one start or go abouts to fixing the low impedance? would these pictures posted above of the pin holes be causing a low impedance? or is it more so of an actual failed component like a resistor or the out put transistor from what i read on other forums hmm. I guess my first step is going to be resoldering these pin hole connections, not gonna mess with the bridged soldering jobs quite yet, but after watching some other videos online, pausing the video i could see that many other PCB's for certain amps i noticed bridged solders.
     
  6. JCGdes

    JCGdes New Member

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    Well i took the 10 inch 4ohm speaker out of the 30cfx, the one that still has a faint a bit of dirty sound, and it gets a bad .1 ohm reading ,but still has some continuity on the connectors.

    Ripped out both the 12 inch 8ohm speakers from the 102cfx, and neither one of them have any continuity, or any ohm reading what so ever on the multi meter. Even tried each one of the 12 inch speakers in the 30cfx and had no sound what so ever, plugged the 10 inch back in and it still has a faint sound.

    So all in all i guess its safe to say, Both these amps speakers are fried.

    I still have a bit of hope for the 30cfx considering it had that damaged capacitor pictured above as well as a one or two pin hole solders, but I am not to optimistic at this point.

    My only other option is to see if i can find some Cheap speaker replacements some where just to test them out.
     

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