OCD debug help please. Voltages included

[woodster123]

Hi,

I've built myself an OCD on vero following this layout/schematic:



I've substituted a 22nf for C1; 100nF for C2; 2x 100pF in parallel for C9.

Bypass works fine but nothing with the effect engaged.  If I remove the TL072 and jumper pins 3 and 7 I get throughput, Tone and Vol controls seem to be working ok.

Voltages on TL072 are:

Pin 1 4.55v
Pin 2 4.55v
Pin 3 4.35v
Pin 4 0v
Pin 5 4.54v
Pin 6 1.471v
Pin 7 8.49v
Pin 8 9.1v

With TL072 removed, voltages on socket pins are:

Pin 1 4.12v
Pin 2 4.12v
Pin 3 4.36v
Pin 4 0v
Pin 5 4.12v
Pin 6 0.145v
Pin 7 0.6v
Pin 8 9.12v

[woodster123]

Voltages at 2N7000's (with TL072 socketed):

Q1
s 4.55v
g 4.54v
d 4.54v

Q2
s 4.55v
g 4.54v
d 4.53v

With TL072 removed:

Q1
s 4.55v
g 4.12v
d 4.12v

Q2
s 4.11v
g 4.55v
d 4.55v

[woodster123]

D1 (TL072 socketed)
A 9.08v
K 0v
(TL072 removed)
A 9.11v
K 0v

D2 (TL072 socketed)
A 4.53v
K 4.53v
(TL072 removed)
A 4.11v
K 4.11v

If any other readings would be helpful let me know and I'll post them.

Thanks in anticipation!

[anchovie]

TL072 pins 6 & 7 should be reading approximately 4.5V. Check connections for the components coming off those pins.

[woodster123]

Thanks for the advice.

I missed the little jumper immediately below C10 on the layout.  Also found a tiny solder splash between two tracks.

I'm getting 4.5v on pins 5, 6, 7 now so it's looking good, I'll give it a proper test tomorrow.