Easy Vibe Debug

[MmmPedals]

Got this cheap from another forum member. Its etched on RG's layout at geo. schematic is here http://www.hollis.co.uk/john/easyvibe.jpg
Using LED and LDR in shrink wrap. There were a number of components in backwards but i believe the LED's are correct because at one point when I would touch pin 1 of U4 it worked perfect (although this has stopped happening after I touched up some joints).
Passes a dry signal but no effect.
Bias led's glow fine
No battery. 1Spot at 9.56v
U1
1-3.26  8-9.56
2-3.36  7-3.26
3-0.3    6-3.26
4-0       5-3.26

U2
1-3.26         8-9.56
2-fluctuates  7-3.26
3-3.26         6-3.26
4-0             5-Depends on light (~0.6-1.5)

U3
1-2.15   8-9.56
2-2.15   7-3.26
3-2.67   6-3.26
4-0       5-Depends on light

U4
1-8.84   8-9.56
2-3.26   7-3.25
3-0.65   6-3.25
4-0       5- Depends on light 

[MmmPedals]

Does anyone have a redrawn schematic?
Would make debugging a bit easier.

[MmmPedals]

I said that I had it working when I touched pin 1 of U1. I meant pin 3 (I tacked a lead onto  r20/u1 3 junction and) when I touch it I get the effect.
when I peak into the shrink wrap I think only LED 1 is on. Before i rip them out and replace them I would like know...
Could LED's oriented improperly throw off the voltages?

[MmmPedals]

AAAAAARGGGGGGG
Just replaced all the LED/LDR. flashing nicely now but..,. ONE IS GREEN AND 3 ARE YELLOW. oops   
Anyway its still nor working unless i hold onto the lead by pin 3. 

[MmmPedals]

Just for clarification. If I touch Th junction of the 100k resistor the 47k resistor and pos. In (on bot right of schematic) while also touching ground it works perfect.
If I tie it to ground with a wire it does not work.

Feel like I am talking to myself.

[R.G.]

Feel like I am talking to myself.

Good. Sometimes that's the best way to debug. 

Just for clarification. If I touch Th junction of the 100k resistor the 47k resistor and pos. In (on bot right of schematic) while also touching ground it works perfect. If I tie it to ground with a wire it does not work.

Dry human skin is about 20K-30K. So you're about a 40-60K resistor. Nope, wire is not the same.

If, when you touch something it starts/stops working, there are two good hypotheses to try. One is that the conduction of your body is causing the change, and the other is that the mechanical movement is causing the change. To tell the difference, -> try touching the same point with an insulating wooden stick <- like a matchstick, chopstick, or wooden dowel. The carbon in a pencil is conductive, so you'd have to be careful not to touch the lead inside if you used a pencil.

[MmmPedals]

If, when you touch something it starts/stops working, there are two good hypotheses to try. One is that the conduction of your body is causing the change, and the other is that the mechanical movement is causing the change. To tell the difference, -> try touching the same point with an insulating wooden stick <- like a matchstick, chopstick, or wooden dowel. The carbon in a pencil is conductive, so you'd have to be careful not to touch the lead inside if you used a pencil.

It is definitely the conducting because I tried touching very lightly. I also cheched and double checked the joint. Even replaced the resistor I tacked the lead onto.

[R.G.]

It is definitely the conducting because I tried touching very lightly. I also cheched and double checked the joint. Even replaced the resistor I tacked the lead onto.

So - if it's a conduction problem, what is different about this PCB from the schematic? What is not connected to ground or defective that adding a resistor to ground here corrects? Does your multimeter measure the correct resistances from that point to other places through various resistors and caps?

[MmmPedals]

would a blown diode from the in the LFO make it malfunction. I checked everything else to the point that i think it must be one of those.
I will switch them out out when I get the will to do it.

[juancra]

Hi!
I'm sorry to revive this post, but I have the exact same problem as this guy: my build only works if I touch pin 3 of u1 with a pencil. I checked all resistors, I removed the input cap and happens the same, do you have an advice?