OSP TS808 no sound

[satrian]

Hey guys, just finished mi OSP TS808 and there is no sound at all when engaged, just a low static noise.
It all seems to be okay, IC voltages are as follows:
1- 4.58
2- 4.58
3- 4.57
4- 8.89
5- 4.47
6- 4.86
7- 4.56
8- 0.20

I'm really baffled as to what might be happening. Any advice or help is greatly appreciated.

[mgwhit]

IC voltages are as follows:
1- 4.58
2- 4.58
3- 4.57
4- 8.89
5- 4.47
6- 4.86
7- 4.56
8- 0.20

Your power and ground pins appear to be reversed.  You should be getting power (the 8.89V above) on pin 8 and ground (0V) on pin 4.  Do you have the chip in backwards or are you counting pins incorrectly?  (Notch up, start in top left corner, count down left side, then up the right side.)

Assuming you're just counting incorrectly, you should still just have 0V on your ground pin, so (with the power disconnected from the board) check for continuity between that pin and ground.  It might just be a cold joint on that pin or somewhere along the ground path.

There are plenty of other things that could be wrong, too, including the switching or a short anywhere else on the board.  Please post your transistor pin voltages and decent photos of both sides of the board.  Take some time with your multimeter's continuity function to trace connections, and if you can take the time to build a signal probe and tell us where you lose signal that would be a tremendous help.  Good luck!

[satrian]

Done! On my many rounds looking at the PCB copper side and solders, I had missed a defect in the etching of the PCB that created a gap where there was supposed to be a track. Bridged that with a little solder and now it's working as expected.

I'm still concerned about the pins 8 and 4... I am counting them correctly and 4 i connected to the ground plane on the PCB.

[satrian]

UPDATE: think I got is figured out. Before I was taking the readings with the positive tester probe connected to the +9v wire and then the negative tip to each IC pin. Then I realised the I should be measuring potencial difference and the better way to do that would be to put the negative tip on the ground of the circuit and then the positive tip to each IC pin.

Please confirm if my reasoning was correct.

[mgwhit]

When measuring voltage in one of these circuits, you're usually measuring in relation to ground.  Unless I'm measuring across a specific component, I clip my black lead to ground and use the red lead to probe the pins/leads.

[satrian]

When measuring voltage in one of these circuits, you're usually measuring in relation to ground.  Unless I'm measuring across a specific component, I clip my black lead to ground and use the red lead to probe the pins/leads.

Thank you. Other thing I found... at least for this circuit, 1N4148s sound better than red leds. =P