Fender Frontman 212r buzzing help

BadBoyKaneBadBoyKane Frets: 2
I need a little help from anyone in the know or anyone who has had a similar problem and fixed it.

The Frontman 212r has developed quite a significant problem and can be heard here on the clean channel and as you can here the buzzing is something else, it's exactly the same on the drive channel too and both inputs.

http://s162.photobucket.com/user/badboykane/media/Sale/EE2F1D95-EC61-4CF7-8B1D-2D96C87A9AD6_zps0dppgu14.mp4.html

I am am more than capable of changing components, checking cubits with a multimeter etc but hoping for a little guidance on what I should be looking for most to identify the fault.

i would greatly appreciate anyone who can help a little on this as I'd really like to get it working and it gives me additional knowledge if I get it working.

thanks guys in advance
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Comments

  • ICBMICBM Frets: 71956
    There are two common faults with these amps - blown speakers, and two high-power resistors which are a bit under-spec and desolder themselves from the PCB. From the video I would guess more likely to be the latter, but check the speakers first by disconnecting one at a time (and don't turn the amp up full).

    The resistors can be fixed without taking the PCB out if you know where to jumper them to the next component in the circuit (I would need to check, can't remember off the top of my head), but taking the board out isn't too bad a job really. You can usually resolder them effectively if you clean the solder off the joints, crimp the leads down tightly onto the board and resolder. Or if you want to do it really thoroughly, replace them with the next power rating up (7W instead of 5).

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Thanks man, that's some detailed info there. The speakers are fine as I've just tested them with another amp.
    I'll have a look at the resistors tomorrow when I get a chance and see if I can spot any of the resistors and I'll order some new ones and replace them if that's the case.
    i hope it is and thanks for your time to help
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  • ICBMICBM Frets: 71956

    I'll have a look at the resistors tomorrow when I get a chance and see if I can spot any of the resistors and I'll order some new ones and replace them if that's the case.
    They're two large rectangular white resistors, near the back edge of the PCB near the input jack end from memory. See if they feel loose - if so that will be it. So far I've repaired them by resoldering the existing resistors - once I was in a hurry for someone so I did it by adding jumper wires to the next components. None have come back so far.

    To date these are the only faults I've come across with these amps - about three each I think - although that doesn't rule out something else…

    Despite this and the tendency to blow the speakers I still think they're very good amps for the money.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Thanks for your help @ICBM ;
    i got the amp used and upon opening it all up and lifting the circuit board I can clearly see it has been repaired before but a real bad solder job, it was the two resistors you mentioned, the 330r ones, I have resoldered them so they are not loose and so far so good, all seems well with the amp and it's lovely and clear.
    Those two resistors do get extremely hot though so that would explain why they had melted the solder.
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  • jpfampsjpfamps Frets: 2723
    ICBM said:

    I'll have a look at the resistors tomorrow when I get a chance and see if I can spot any of the resistors and I'll order some new ones and replace them if that's the case.
    They're two large rectangular white resistors, near the back edge of the PCB near the input jack end from memory. See if they feel loose - if so that will be it. So far I've repaired them by resoldering the existing resistors - once I was in a hurry for someone so I did it by adding jumper wires to the next components. None have come back so far.

    To date these are the only faults I've come across with these amps - about three each I think - although that doesn't rule out something else…

    Despite this and the tendency to blow the speakers I still think they're very good amps for the money.



    These are not my favourite amp to work on; the power stage is overly complex and mute circuit can fail and latch the power amp up to the positive rail.

    I've had a couple of these in with (at least to me) intractable problems in the power stage, that could only be sorted by disconnecting the mute circuit (this mean't there is a thump at power up, but didn't seem have any other detrimental effects.

    Out of curiosity, I made a major effort to try to find the problem in one of these amps, and was totally stumped.

    The amp would randomly latch up to the +ve rail. This could be reversed by applying freeze spray to one of the small signal transistors in the power amp, but changing the resistor didn't resolve the issue. In the end I gave up!


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  • ICBMICBM Frets: 71956

    Those two resistors do get extremely hot though so that would explain why they had melted the solder.
    That's why I've considered upgrading their power rating, although not actually put that into practice yet. Standing them off from the board would help too.

    I am not a fan of this type of voltage regulation, it's difficult to make it totally reliable without overkill on the resistor and Zener sizes, which costs companies money so they won't unless the warranty rate is just too big. (As it was on the original Blues/Hotrod Deluxe/Devilles.)

    jpfamps said:

    These are not my favourite amp to work on; the power stage is overly complex and mute circuit can fail and latch the power amp up to the positive rail.

    I've had a couple of these in with (at least to me) intractable problems in the power stage, that could only be sorted by disconnecting the mute circuit (this mean't there is a thump at power up, but didn't seem have any other detrimental effects.

    Out of curiosity, I made a major effort to try to find the problem in one of these amps, and was totally stumped.

    The amp would randomly latch up to the +ve rail. This could be reversed by applying freeze spray to one of the small signal transistors in the power amp, but changing the resistor didn't resolve the issue. In the end I gave up!
    I haven't come across that yet, but I'll take note - thanks. I'm also not a fan of muting circuits just to do things like stopping power-up thump. It's more complication than really necessary and which potentially causes trouble.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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