+B and -B voltages high??!!?!

[emmett]

so i'm consistently getting 28.1 and -26.1 Volts when testing between U3 and U4 and U4 and U5 (+B and -B). I've been testing everything i can on this board to see what might have happened but everything's measuring the same as my buddy's working A12 except R14 and 15. mine are reading 21K6 and 19K5 (they're listed at 22K ohms) and his are reading 12K7.

any ideas?

[tpryan]

So no matter what you do to R25 and R29 you can't adjust the voltages below +28/-26?

[emmett]

correct. started with the pots (R25 and 29) all the way counter clockwise and went all the way back without any noticeable change.

[tpryan]

Make absolutely sure you have all the diodes installed the right way round. Also verify that you have not swapped the LM317 with the LM337 regulator.

[emmett]

nope, they are as they should be: U4 is 317 and U5 is 337.

i built my second A12 and am about to hook that up to my power supply to see if i'm crazy. let's see what happens.


.......


well on my second A12, R14 and R15 are both reading 12K9 when installed in the board (the same as my friend's working A12's) and the voltage on pins 3 and 4 and 4 and 5 of U1 are 14.4 and -14.4 V with the pots fully counter clockwise. so i'm not sure whether i should laugh or cry.

again, if anybody has any ideas as to why my first A12's R14 and R15 are reading 21K6 and 19K5 ohms and the voltages on the pins of U1 are so high, please let me know. for now, i'm starting up work on my N72s.

[tpryan]

By far the most likely thing is that you have a part in the wrong place, bad solder joints, or a combination of the two. It's just a matter of finding them. Re-flow every joint and measure every part. There aren't that many.