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Post subject: Frontman 25R stuck in drive
Posted: Fri May 04, 2018 8:08 am
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I have read 2 previous threads about this but the threads were dropped before a fix. I would like to actual fix this. Here is what one of the posts says:
"
Sounds like Q1 and Q2 transistors aren't switching off when you switch channels. Since the LED switches on and off, I would expect to see the +13.9 VDC when drive selected, and -13.9 VDC when clean is selected, out of pin 7 of the op-amp U5. That voltage is fed to R54, dropped and then to the cathodes of D5 and D6 which feed the transistors used to switch channels. Do you have the correct voltages at pin 7 of the op-amp? If so, check to see if you get a small voltage change at the gates of the transistors (middle pin)."

I would be happy if I could get the NORMAL channel to work INSTEAD of the DRIVE channel. Is there a circuit trace I could just cut to eliminate the DRIVE section ?
Thanks , Joe


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Post subject: Re: Frontman 25R stuck in drive
Posted: Tue May 08, 2018 9:57 am
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There's a good chance that the problem is overheated soldering on r46. It's the power source for the switching logic.
Its located behind the headphone jack with a brown green red color code.
I would resolder the other large resistors next to it while you are in there, jacks too.


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