Trying to fix a Boss BF2

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Hi folks, I'm currently trying to fix a broken Boss BF2. The problem is that I'm getting no effect sound, just dry signal whether it's on or off.

I got some advice on another forum, and did an audio probe test (though my knowledge is limited and I'm very much a learner at this stage). Anyway, when I was "probing" here's what I found:

I'm getting audio output from one pin on each of the chips except MN3102. None of the pins on that pass the audio through, but a couple of them mute the whole signal, even the hum. So could it be that one that's causing the trouble? And if so, can I replace that with a CD3102, which I have one of lying around?

Also, I get no audio signal from IR9022, but I do get what I think is the clock signal from one of the pins, and it changes speed when turning the rate knob. Is that a good sign? The sound itself doesn't come through that, but does the pulse indicate that that one still works?

Any help or advice on what I should do next would be very much appreciated. Cheers!

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Comments

  • lasermonkeylasermonkey Frets: 1940
    edited October 2018
    The 3102 is the clock driver for the 3207, so you won't be getting any audio from it.

    I suspect it's not the flip-flop switching circuit, as (presumably) the LED is switching on and off, though it's possible that the Q4 (the FET that is toggled on and off by the flip-flop circuit (and thereby passes the wet signal) may be borked. You could check that by temporarily linking the source and drain of that FET- if that doesn't pass wet output, then it's something else.

    IC1 is definitely working, as this does the pre- and de-emphasising and is always in circuit, even in bypass. This leaves IC2, IC3, IC4 and the associated components. You can rule out IC5 (the TL022/IR9022) as that's used for the LFO and if that wasn't working but the BBD was, you'd hear a "drainpipe" type effect, basically the very short delay from the BBD chip. I would suspect that it's either the 3207 or the 3102, as they are both somewhat sensitive chips.

    I can't say I'm familiar with the CD3102. I had a look for the datasheet but couldn't find anything. You can get MN3207/3102s (and the Coolaudio clones) from some of the German DIY audio shops, such as Banzai or UK Electronic. They weren't expensive last time I bought some. If you do decide to try replacing them, put them in sockets as it will make any future swapping much easier.

    It's also well worth getting a good, powerful magnifying glass and having a look for broken tracks or solder joints which may have failed. I've repaired a few pedals where these have happened, and it's often very difficult to spot with the naked eye.

    Good luck!


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  • Any joy?
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  • Oh, and check the bias.
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