Boss DF-2 Super Feedbacker and Distortion Repair

[Dasher]

I have a Boss DF-2 Super Feedbacker and Distortion (schematic here: https://imgur.com/gallery/bsMP9fb and effect info here: http://www.bossarea.com/boss-df-2-super-feedbacker-distortion/) that I recently purchased as broken. The distortion portion of the circuit works well. However, the feedback effect that's supposed to be triggered by holding down the footswitch does not work properly. Instead of the expected sustaining feedback effect, my DF-2 produces an oscillating siren-like noise. A google search revealed that others have encountered similar problems with this pedal. In fact, it looks like some people mod their DF-2s to produce this siren noise instead of the standard feedback effect. Here's someone else's youtube video demonstrating the usual feedback effect and the siren effect that mine produces (https://www.youtube.com/watch?v=SjhLvAyTLYw). I don't think that my pedal has been intentionally modified; it doesn't look like the PCB or components have been altered.

While some people may like this siren noise, I'd like to get it working properly as it was designed. Does anyone have any thoughts regarding what portion of the circuit may be malfunctioning? Thank you in advance to anyone who's willing and able to take the time to help me out.

Here are my voltage measurements:

IC1 (M5218) – These all look good to me
1 – 4.85
2 – 4.85
3 – 4.79
4 – 0
5 – 4.79
6 – 4.85
7 – 4.85
8 – 9.70

IC2 (IR9022) – These all look good to me
1 – 4.80 ~ varies
2 – 4.90 ~ varies
3 – 4.80 ~ varies
4 – 0
5 – 4.55
6 – 4.86
7 – 4.86
8 – 9.70

IC3 (IR9022) – These all look good to me
1 – 4.88
2 – 4.88
3 – 4.85
4 – 0
5 – 4.85
6 – 4.88
7 – 4.75
8 – 9.71

IC4 (IR9022) – Suspect voltages on this IC?
1 – 5.60
2 – 4.85
3 – 4.85
4 – 0
5 – 4.85
6 – 4.88
7 – 2.75 *This seems low
8 – 9.71

IC5 (HD14013) – Suspect voltages on this IC?
1 – 1.98 *Should this be the same as pin 2? Schematic shows them connected by dotted line
2 – 2.96 *
3 – 0
4 – 3.28
5 – 0
6 – 1.98
7 – 0
8 – 0
9 – 0.35 ~ varies
10 – 0
11 – 4.4 ~ varies
12 – 0.40 ~ varies
13 – 4.3 ~ varies
14 – 4.94 ~ varies

IC6 (78L05) – These all look good to me
I – 9.70
O – 4.94
G - 0

IC7 (HD14046)
1 – 3.60 ~varies
2 – 2.00 ~ varies
3 – 4.30 ~varies
4 – 4.40 ~varies
5 – 0
6 – 0.10
7 – 0.05 ~varies
8 – 0
9 – 1.96
10 – 1.08
11 – 0.08
12 – 3.54
13 – 1.96
14 – 2.99
15 – 0.58
16 – 4.94

IC8 (HD14066) – Suspect voltages on this IC?
1 – 1.97 *I measured 1.09V while double checking my readings. Seems odd
2 – 1.97 *I measured 1.09V while double checking my readings. Seems odd
3 – 0
4 – 0
5 – 0
6 – 0
7 – 0
8 – 4.70 ~varies
9 – 0
10 – 0
11 – 0
12 – 9.40
13 – 8.99
14 – 9.70

IC9 (HD14001)
1 – 9.60
2 – 9.60
3 – 0
4 – 0
5 – 6.95
6 – 9.44
7 – 0
8 – 0
9 – 9.60
10 – 0
11 – 9.60
12 – 0
13 – 0
14 – 9.70

[Dasher]

Just a quick update on my progress with this repair. I went over the board and reflowed the solder on all joints, just in case there was a poor joint that I wasn't able to see. I still have a siren noise maker .

I thought it'd be a good idea to record a video demonstrating my problem. Please let me know if it triggers any ideas. Thanks!

Link is here: https://www.youtube.com/watch?v=nSmo-VarJjI&feature=youtu.be

[Rob Strand]

Just looking casually at the circuit:  I'd expect C37 to hold the voltage corresponding to the note.  The LFO feeds C37 via a very high impedance (C36).   I don't think the amount of modulation should be as much as in the video if C37 was in circuit (I could be wrong since I haven't tried to look at the voltages and expected frequency shift.)

When you removed the LFO is kind of locks to the note indicating something is working at least.  So maybe the "hold" supplied by C37 is broken.

- Any bad solder joints around C37 and maybe R68, IC 8a pin 1, pin 2?
- Is C37 damaged?
- Is there any contamination of the PCB that could discharge C37?

[Dasher]

Thank you for your help, Rob. You nailed it! I got it working.

One of the pcb pads for C37 had separated, ever so slightly, from the board. The feedback function works properly now that I've corrected that.

Thanks again for lending me your brain power.

[mimmotronics]

For future reference, the dotted line connecting pins 1 and 2 on IC5a does not indicate they are connected, it means that either pin 1 OR pin 2 might be connected there. IC5 is a 4013 D Flip-Flop where pins 1 and 2 are complementary outputs, so it would be extremely odd for them to be connected together.

Glad you got it working!!

[Rob Strand]

I got it working.

Cool.  (I'm actually glad it didn't turn out to be one of those frustrating problems where none of the suggested solutions work!)

For future reference, the dotted line connecting pins 1 and 2 on IC5a does not indicate they are connected, it means that either pin 1 OR pin 2 might be connected there. IC5 is a 4013 D Flip-Flop where pins 1 and 2 are complementary outputs, so it would be extremely odd for them to be connected together.

I noticed that as well.  It's a weird thing to have on a schematic.  I don't know if they are trying to say it *could* go to either for PCB layout purposes. When I traced the PCB in the service manual it goes to pin 1 (it has to go to one or the other.)

[Dasher]

For future reference, the dotted line connecting pins 1 and 2 on IC5a does not indicate they are connected, it means that either pin 1 OR pin 2 might be connected there. IC5 is a 4013 D Flip-Flop where pins 1 and 2 are complementary outputs, so it would be extremely odd for them to be connected together.

Thanks for the explanation regarding pins 1 and 2 on IC5. I had never noticed a dotted line like that on a schematic before; now I know if I see it again.

I got it working.

Cool.  (I'm actually glad it didn't turn out to be one of those frustrating problems where none of the suggested solutions work!)

You and me both!