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HELP! My amp is behaving strangely… Can it be fixed?

Discussion in 'Amp Input - Normal or Bright' started by waltschwarzkopf, Dec 21, 2017.

  1. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    Hi guys,

    I have a small practice amp that I bought back in the year 2000. It has served me well at home, studio and garage practice; sadly, now is behaving strangely.

    It is a 15W solid-state Marshall combo model G15RCD, in case you have not heard of it, here are some links:

    Reviews: https://www.ultimate-guitar.com/reviews/guitar_amplifiers/marshall/g15rcd/

    Manual: https://www.manualslib.com/manual/99221/Marshall-Amplification-G15rcd.html#manual

    Although it is a small amp, the volume stays on 2-3 for home practice. It has only one channel, so I set it to crunch and change the gain with the volume controls of the guitar.

    The problem is that after playing it for a short while the sound starts to go on and off, then the gain goes until it the sound disappears completely. I have to crank it up all the way to 11 so be able to hear a clean sound at low volume. If I stop playing it for a while, it goes back to normal. This does not happen every time I play it, but it does happen with all of my guitars, so it is not a guitar nor a cable problem.

    What do you think? Can it be fixed? I am quite handy with electronics and I like rewiring my guitars, but I have never worked on an amp before. I have heard on other amps that you can replace the OP amps, capacitors and other parts, but I do not know where to start! I have checked the connection to the speaker and it seems fine, although I will disconnect it and clean the contacts just to be sure.

    I hope that you can help me on this, I really like the sound of the amp and would be very sad to let it go.


    Cheers!

    Walter


    P.S. If you live in Zürich and want to get together and jam, send me a PM and bring two amps!
     

  2. Stratoholic

    Stratoholic Senior Stratmaster

    Mar 30, 2010
    somewhere
    It can be a number of things, power supply, an IC, broken solder joints, worn jacks and so on. But as far as replacing the amp, I wouldn't worry much. They make a much improved version:
     

  3. Stevem

    Stevem Strat-O-Master

    940
    Sep 3, 2014
    NY
    The output IC chip is failing I would bet!
    Put the amp out in the cold over night Or in your refrigerator for 2 hours , then play it, does it take longer to act up?
    If so then my gues on the output IC is right and even though these chips cost less then 20 bucks it may not be worth fixing the amp?

    I at that point would get a estimate from a repair shop!
     

  4. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    Thanks, I'll try "cooling" the amp and also see if this changes after not playing it for a week.
    Regarding the failing part, is the "IC chip" the same as the "OP amp"? If so, I can buy them online for very little money and I'm willing to do the job myself. After all, if the amp is as good as dead, then I have nothing to lose if I mess it up, right?
     

  5. Stevem

    Stevem Strat-O-Master

    940
    Sep 3, 2014
    NY
    It's a output IC pack that gets both soldered in with like 14 metal leads and bolted down to the chassis for a heat sink.

    You likely do not have the needed vacuum desoldering station to just get the leads out so what you need to do is clip all the leads one at a time making room to get at the rear leads since they are staggered as you go.

    Then you can go back and heat up and yank out the clipped off ends, it's not much fun to have to do it that way , but it can be done!
     
    vid1900 likes this.

  6. vid1900

    vid1900 Senior Stratmaster

    Nov 25, 2016
    USA
    Look for any bulging/leaking capacitors on the circuit boards.


    A quick way to find thermally defective components:

    Open up the amp and play until the problem starts.

    Take a can of Canned Air (like you used to dust CDRs off with 25 years ago), tip it upsidedown, and using the straw, spray the frost onto one chip at a time.

    If freezing a chip fixes the problem, you got your troublemaker.
     

    Attached Files:

    Yves likes this.

  7. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    Hi guys,

    Merry Xmas and Happy New Year to all of you. Here's an update on the status of the amp.

    After letting it rest for a week, I plugged it in again to have a jam. I was very sad to find out that it did not work at all, even with the volume cranked to 11 no sound came out of it. To make things worse, it makes a horrible high-pitched noise that can be "controlled" with the Gain1 knob, at 10 is loudest and below 5 is almost unnoticeable.

    I opened it up to have a look and the board and all the elements seem ok, I'm not an expert but there were no loose wires, exploded capacitors or burned components. All the knobs turn smoothly and everything else is tightly in place. The Gain2 knob was a bit darker on the back, but that was not the problem with the high-pitche noise nor with the volume issue. I put it back together and reconnected the speaker and it was still the same, no guitar sound, only the horrible pitch.

    I'll appreciate all the help you can give me. Otherwise, I'd have to declare it legally dead and find a used equivalent or go for a new amp (Bassbreaker 007 comes to mind).

    Cheers,
    Walter
     

  8. heltershelton

    heltershelton ASKED TO LEAVE THE STAGE Strat-Talk Supporter

    Jun 5, 2013
    Not Florida
    its 18 years old. its dead. look on the bright side......youre gettin a new amp!
     
    s5tuart, waltschwarzkopf and kchurch like this.

  9. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    I saw a used Hughes & Kettner Blue Edition 15R for 90CHF. It's pretty much the same as mine and according to the reviews it looks to be a good sounding amp. What do you think?
     

  10. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    BREAKING NEWS!!!

    Hi guys, I haven’t given up on my old friend yet. I brought some tools and other components home and I think I’ve managed to track down the problem.

    Hear me out:

    If I connect my phone to the CD input, it sounds great. I control the volume from the phone and there is no hum or annoying pitch. Which means that the speaker works.

    If I connect the phone to the guitar input it also works AND I can change the volume, gain and EQ settings from the amp. Which means that the amp controls work too!

    If I connect my guitars (all of them passive) to the amp input, no sound comes out (hence the thread). BUT if I connect the guitar to an amp app on my phone and then the phone to the guitar input, it works!! And all the controls too.

    I wouldn’t like to run the amp like that, because it’s a bit annoying with all the cables. But it makes me think that the Voltage from the guitar is too low to drive the amp, as the phone output does drive it well. Since the output of the guitars is the same as always, it must be something between the guitar input and the amp itself.

    Could be a loose connector somewhere? The OC amp?

    Come on guys! I’m really close on this one and I know that the problem is simple and there is still live in the old amp.
     

  11. rudos1

    rudos1 Senior Stratmaster

    Aug 16, 2013
    Boston
    Bad guitar cable? I guess it works connected to your phone but maybe test with another known good cable?
     

  12. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    Change the input jack and your amp is back to business.
    It is a cliff jack (they are crap) and Marshall is using those since the mid ´80s for no reason.
    You have to find the right part for the MG series(!).
    It is a bad ground connection on the input jack and maybe (I guess) it works fine with your phone because you are using a stereo plug which makes the "right" connections.

    If it is in fact your guitar cable you know we have to kill you for that xD.

    All the best,
    Robin
     

  13. fezz parka

    fezz parka Off.... Strat-Talk Supporter

    Apr 21, 2011
    Undisclosed.
    I thought I was the only one who thought this. Thanks Robin!
     
    carver and Robins like this.

  14. Yves

    Yves Senior Stratmaster

    Jan 2, 2016
    London
    so it seems your amp is fine and it's an issue with how the signal is transferred to the amp. have you tried different input jacks?
     

  15. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    Hi guys,

    I'm glad to tell you (but a bit embarrassed) that it seems that the problem was the cable after all. I borrowed one and it worked, I played it continuously for close to one hour and no problems arose. I'll keep on testing it and see it everything is still ok.

    Thanks a lot for your help.
     

  16. apm1991

    apm1991 Senior Stratmaster

    Age:
    27
    Feb 14, 2017
    Arizona
    If you buy a new amp.. buy a Katana 50.. it has a .5 watt setting so perfect for home use, 25 watt setting for small gigs and practice, and 50 watt setting for bigger venues or outdoors... They are $220 now, but if you call musicians friend and ask for a promo code for it or discount they will it down to $187.. just got one for the lead guitarist in the band
     

  17. Inverness

    Inverness Senior Stratmaster

    Age:
    50
    Dec 24, 2013
    Salt Lake City
    Glad to hear you got it figured out. Of course, now @Robins is on his way to Zurich from Germany...;)
     

  18. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    This one is for @waltschwarzkopf - just a little reminder for the next time before I am on my way with my friends Smith&Wesson xD



    Life is good,
    Robin
     

  19. waltschwarzkopf

    waltschwarzkopf Strat-Talker

    Age:
    33
    113
    May 17, 2017
    Zürich
    I was thinking more like Sig & Mauser ;)
     

  20. rudos1

    rudos1 Senior Stratmaster

    Aug 16, 2013
    Boston
    It figures but glad it was an easy answer!!