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starr36
Platinum Member
Canada
1172 Posts |
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stahlhart
Platinum Member
1318 Posts |
 Posted - 03/26/2006 : 03:52:14
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It appears that the pedal is at least partially functioning -- signal has to travel through Q1 and Q2 before it reaches the direct out. I confirmed this to be true with one of my working DD-2s.
IC9, the BA634, appears to fire the indicator LED from actuation of the footswitch. The switching circuitry is powered by the 9v side of the supply, so if the power is allowing direct signal out then there's probably power here also -- the BA634 or its support circuitry (Q7, Q11, Q12, Q13) could be bad. IC9's output fires the LED and passes through wet signal via switching on Q8.
That's my inital wild-assed guess, anyway...
C.K.
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stahlhart
Platinum Member
1318 Posts |
Posted - 03/26/2006 : 04:03:35
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I'd also be suspicious of grounding on the circuit path from pin 2 of IC9 through to the gate of Q8 and the indicator LED, possibly by a completely toasted IC9. I'd measure resistance to ground on that path both with it IC9 installed and also removed from the board.
C.K.
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stahlhart
Platinum Member
1318 Posts |
Posted - 03/28/2006 : 02:15:52
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Looks like I'm going to be given the opportunity to defend my thesis...    
C.K. (hopefully in that order)
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starr36
Platinum Member
Canada
1172 Posts |
Posted - 03/28/2006 : 02:56:52
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quote:
Originally posted by stahlhart
Looks like I'm going to be given the opportunity to defend my thesis...
C.K. (hopefully in that order)
Let us know how you make it. Too bad dinglenuts there with 23 feedbacks doesn't know how to ebay. Just bidsnipe, folks, just bidsnipe.
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stahlhart
Platinum Member
1318 Posts |
Posted - 03/28/2006 : 03:16:20
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I'll keep you posted...
C.K.
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stahlhart
Platinum Member
1318 Posts |
Posted - 04/05/2006 : 02:09:41
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Well, how about that.
This broken DD-2 arrived. And -- for the second time in a row -- it was a shorted D6 Zener diode. I think that I've identified a common failure on this pedal, now that I've seen it again.
Again, the battery overheated -- only this time, the diode got so hot that it apparently desoldered itself from the board. I'm having a hard time believing this, but here's what happened: I put a battery in, plugged in cables and started examining things, and while I'm abouit a minute or so into that, I detect that smell familiar to those of us who do repair work... touch the side of the battery, and it's red hot. Disconnect battery, and take the pedal into my bathroom -- I know that sounds strange, but the reason I did this is that it's the brightest lit room in my condo I at the moment, and I needed some good light to be able to see which component on the board burned. And I happened to be near the sink when I flipped the pedal and the circuit board over -- and then I heard a clink... the diode fell off the board and down the drain. 
All of the solder connections on the board were good when I first pulled the bottom panel off. I still can't believe a battery supplied enough current to get the diode hot enough to melt the solder connections clean through.
Anyway, I brought the pedal back into the office, plugged in a fresh battery -- and now everything is working...  compared it to my other two DD-2s, and it sounds pretty much the same. The Zener diode is just a reference voltage to ground; it's absence from the board really doesn't matter with battery power. I'll still replace it, though.
starr36: let's talk...
C.K.
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starr36
Platinum Member
Canada
1172 Posts |
Posted - 04/05/2006 : 03:17:02
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That is so cool.
I still can't figure out why one my DD-2s can't see the feeback control. Dang - I should be so lucky.
That smoking hot battery must have given you a momentary thought of a bomb or something!
Great story!!!!!! |
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phostenix
Gold Member
USA
754 Posts |
Posted - 04/05/2006 : 07:51:43
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Zener diode D6 is a voltage regulator to help protect against people connecting power adapters that are higher than 9v. It's not uncommon for a zener to fail as a short (instead of an open). Now you've got a dead short across the input power - your battery in this case. I'm not sure what kind of current a 9v battery can deliver into a dead short, but it doesn't surprise me than it got hot enough to melt solder. I have a pedal that someone overvoltaged & the diode exploded & burned through the PCB trace at the same time. What a mess.
Grace and pecae,
Steve
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OK TECHIES can YOU fix this DD-2 ....
