ms2 pcb testing-found curious electrical readings

[macambra]

While performing the voltage checks on my pcb at the U1 socket,I came across some spts that are suposed to be grounds- but instead I have 5v. The manual says I should have 5v at 1,20,31- which I have. However, I also have it at 19,32 and 1.4v on pin 2. I also don't have 12v on pin 16 only 4v. I followed the troubleshooting guide and everything checks out. I just have the extra voltage.

 

Any ideas?

 

Update- Found that CLT pot on jimstim drops the voltage on pin 16 all the way down to mV. I verified the diodes several times. I have the correct voltage to the proto area. I verified there is no continuity between legs of the trannsisters. I don't want to tear out componants untill I have some idea where to look.

 

Update2- The jimstim on board voltages have dropped- 12v has now dropped to 2.8, 3.3 has dropped to 1.8 . I have verified incomiiing power at 12.17v and is rated up to 2.6A.

 

Update 3- Jimstim has short in 3.3 v cicuit. Everything tested perfect after I built it. It has degraded since then. It was the D4 diode.

 

Update 4- It looks like I could have a short in the C20 cap on the pcb, based on tracing the circuit in the schematic. I will test it when I get home from work.

Edited January 9, 2012 by macambra

[macambra]

While performing the voltage checks on my pcb at the U1 socket,I came across some spts that are suposed to be grounds- but instead I have 5v. The manual says I should have 5v at 1,20,31- which I have. However, I also have it at 19,32 and 1.4v on pin 2. I also don't have 12v on pin 16 only 4v. I followed the troubleshooting guide and everything checks out. I just have the extra voltage.

 

Any ideas?

 

Update- Found that CLT pot on jimstim drops the voltage on pin 16 all the way down to mV. I verified the diodes several times. I have the correct voltage to the proto area. I verified there is no continuity between legs of the trannsisters. I don't want to tear out componants untill I have some idea where to look.

 

Update2- The jimstim on board voltages have dropped- 12v has now dropped to 2.8, 3.3 has dropped to 1.8 . I have verified incomiiing power at 12.17v and is rated up to 2.6A.

 

Update 3- Jimstim has short in 3.3 v cicuit. Everything tested perfect after I built it. It has degraded since then. It was the D4 diode.

 

Update 4- It looks like I could have a short in the C20 cap on the pcb, based on tracing the circuit in the schematic. I will test it when I get home from work.

 

 

OK. I made a rookie mistake. U1 pin#1 is lower right not lower left. I'm an idiot.

 

Thanks for looking!!