Help with BSIAB2 Troubleshooting

[blues_mang]

Ok, I've spent enough time debugging this myself; it's time to ask for some help. I've built the BSIAB2 using the layout from GGG. I etched the board myself... no problem there. The problem I'm having, I think, is a ground issue that I can't seem to wrap my head around. Somehow it seems, I'm grounding my input because I'm getting no sound in bypass mode. I think I'm grounding my input because using my audio probe, in bypass mode, the signal doesn't even get to the first lug of the footswitch. When the pedal is engaged, it's fine. Well, it gets to the footswitch. Herein lies my next problem. When the pedal is engaged, I follow the signal with the audio probe through the circuit with no problem, I get distorted signal when the output reaches lug 3 of the Volume pot, but I'm getting no signal out back to the footswitch from the wiper (lug 2) of the volume as the wiring diagram shows on their site. I'm basically using star grounding. I have my 9V DC jack's ground to the ring of the input jack and ground wires running from the output jack sleeve to the input jack sleeve, from the left side ground pad of the PCB to the input sleeve, and the ground from the footswitch to the input sleeve. The only other ground is lug 1 of the Drive pot is connected to lug 1 of the Volume pot which in turn connects to the right side ground pad of the PCB. I've reflowed all my connections and I get the same thing. No signal in bypass and signal stops at the Volume pot when it's engaged. What the heck am I doing wrong??

[Ed G.]

First off, you need to buy, borrow or steal some sort of continuity tester. Many multimeters come with this function. If the signal is being grounded, you need to find out for sure and the only way to do it easily is with a tester. I've debugged MANY circuits with this and it is just as important, if not more than, the audio probe for debugging.

That said, check the wiring of your switch. Many wiring schemes ground the input of the circuit so there's no oscillation or bleed-through when it's bypassed. Maybe it's grounding the output also/instead.

[John Lyons]

If you have signal on pin 3 of the Volume pot but no signal on the wiper then the pot is bad.
There should be signal on the wiper unless the pot is turned down which grounds the wiper.
Try replacing that pot or measuring it to see that it's working correctly.

If you have no signal in bypass then it's either the switch wiring or you have the jacks wired wrong.
I wired a jack wrong the other day, drove me nuts. It's something simple there.
Clear your head, take a deep breath and follow the GGG diagram again.

EDIT: yeah...if the output jack is grounded somehow you would lose bypass and "on".

john

[gaussmarkov]

perhaps you have reversed the output jack lugs?  are you treating the output jack ground lug as though it were the signal lug?

sometimes a fresh look at the wiring is helpful:  http://gaussmarkov.net/wordpress/thoughts/wiring-up-a-1590b

[blues_mang]

Ed G.,
I do have a multimeter. That was the first thing I used to debug. Thanks for the suggestion though.
  I'm getting continuity everywhere there should be. All the lugs on the footswitch check out. However, when in bypass, I'm getting continuity between the tip lug on the input jack and the sleeve lug (ground) which leads me to believe that I'm somehow grounding my input. I know my footswitch wiring is correct because I've used the same layout for the 20 plus builds I have done without issue before now. The only difference between this and past builds is that I'm using shielded wire for the in and out wires from the jacks. I'm using the shielded wire for the input signal and one side of the copper shielding which is soldered to the sleeve lug on both jacks. I used this on my Dr. Boogie build without issue as well. This really has me stumped.

John,
I was beginning to think that maybe the pot was bad. The only other log pot I have is a 250K, can I make it 100K by adding a resistor in? If so, does it go across outside lugs or outside to wiper?

I'll post a diagram later tonight of how I have everything wired up. In the meantime, I'll keep combing it looking for errors.

[John Lyons]

Without a plug in the input see if you get continuity between the tip and sleeve of the jack.
The input if the circuit board will be grounded in bypass but the input jack should not be grounded in either position.
You also may have over heated the insulation and shorted the input with your shielded wire, it's easy to do.
If you have continuity without a plug in (tip to sleeve) then this is most likely the case.

Are you using shielded wire from the vol pot to the switch?
Maybe another short there...?

john

[blues_mang]

John,
It's got to be my shielded wire. In bypass, I'm getting continuity on the tip and sleeve for both the input and output jacks. I must have overheated them like you said. I'll take them off and rewire. I didn't use shielded wire on the volume pot. Should I have continuity between lug 3 and the wiper (lug 2)?

[John Lyons]

Usually continuity testers only work (beep) when there is 100 ohms or less.
For the volume pot just touch probe tips to 3 and 1 to measure the total resistance. Verify...
Then touch probes to 3 and 2and sweep through the pots rotation. Should go from 0 to 100K (or close)
If both those check out ok then the pot is good.

Shielded wire
It helps to not twist the braid very tight , that way when you solder the braid it's not already pinching into the hot center wire.
When you add heat the braid will short out to the hot wire if you heat it too much.
You can also use a heat sink such as small needle nose pliers or spring loaded clips to keep the heat off the braid or hot center wire.
I usually use Teflon shielded wire for this reason. But that's a whole nother set of challenges.

john

[blues_mang]

Well, that's what it was. I unsoldered the shielded wires and soldered in standard stranded wire and it worked on the first try after that. Seems the pot was fine. I never even thought about overheating the wire and shorting it on itself. I'm pretty happy that it's working. This is the first self etched board I've done and at least there wasn't a problem with the board. If I hadn't tried to get all fancy with the wiring it would have fired up the first time. Hey, every pedal is a learning experience. Thanks for the help guys (especially John).

-BB

[John Lyons]

Cool!
Glad you got it working.
If the wire runs are under 2" or so you shouldn't need to use shielded wiring anyway.

john

[gaussmarkov]

yes, great that you got it working.  and yes, john is a great help to us all.  maybe you should be called the shielded cable guy, john.