Boss SD-2 bypass problem.

[paulyy]

I got this from a friend and he wanted to see if I could fix it. Here's the problem. When I plug it in, The clean singal goes thru with no problems but when I turn it on. I still get the clean singal with the LED on. Opened it up and found a burnt silicon diode. Everything else look good from what I could see. I replaced the silicon diode but still the same issue.
I know the effect still works because when I was testing it. I had my finger on the back of the board and the effect would come thru. I know its not the best way to test or smartest but didn't think about it when I did it.
I'm guessing maybe a transistors or a electrolytic cap needs to be replaced. I could be wrong.
Any help would be great. Thanks

[newfish]

Broken trace would be my guess.

Does the effect come through when you touch in one particular spot of the board?

How much pressure do you have to apply to the board to get the effect to come through?

[paulyy]

No broken traces that I can see. Doesnt take hardly any pressure for the effect to come thru.

[wordstep]

Firstly, get the schematic(Google).

Assume in both channels, you can turn both LEDs on and off. So the Q4 & Q5 is fine, and the control
signals from the TC4011 are fine. Check collecter of Q3 & Q6 when turn the switch on/off, you should get close 0v/9v.

In one side of the R14/R24, you should get 9v. I would think the problem may be  R24/R14/Q6/Q3.

Good luck.

[paulyy]

The first thing i did was look at the schematic and I kinda have an idea as to what might be the problem but not sure.
The LED does come on when you switch channels.
When i get more time, I'll see about swaping out those transister. I'll have to see if smallbear carrys them.
Thanks for the info Wordstep.

[Rob Strand]

I suspect there's a dodgy contact around the mode switch.
It could be the switch itself or the wires to it.

Given the LED works the transistor flip flop is probably working.
Also, it appears the JFET switch are switching properly on dry and effects paths.

An open switch contact seems to fit all the symptoms, and your finger cure.

Check all switch contacts with a multimeter.

[aleister]

recently i had a dunlop wah with the same problem, when i applied slight pressure to te pcb the effect came back to life and at first it appear to me to be the molex type connectors making bad pin contact but it turned out to be a dodgy solder joint. i just reflowed a coupled joints and just like that back to working like a champ. i hope our problem is a simple fix also. - will