4 T-15's built, 2 work....

[mrsteaks]

I just finished 4 T-15's, each built a day apart. The first one and the third one work perfectly. Two and four don't. On the inop modules, the voltages at PGND and the +20 pad are 17.88 volts (on both), but the -20 pad yields -1.55 volts (on both). Uh-oh. The phantom power circuit works correctly. Doing a thorough visual check against the working modules shows that all four are identical - all diodes are in the right direction, polarized capacitors are correct, and regulators are in the right places. So - any ideas????

[tpryan]

Did you measure all the resistors? Check R30 and R33.

[mrsteaks]

R30 measures 120 ohms. R33 measures 9.8 KOhms, and R37 measures 120 ohms. Looks like R37 and R33 are switched, at least on module 2. I'd bet the same thing happened on module 4.

[mrsteaks]

The problem was indeed R37 - I switched it with R33. Everything is now where it belongs and I have four (4) nicely working T-15's. Measure twice, cut once!!

Off to build two C-84's......