JYE Tech Forum

TP21 is +5V?

And TP24 is -2.1V. Suggests that L3 is open circuit or you have a connection to TP24 (AV+) with a -ve voltage on it.

Nice job. I tried mounting a .1uF low-ESR SMD cap in place of C15 with it's ground side actually connected to pin 8 on the IC (via some really fine wire), thus eliminating the wire back to C8. It made no difference. BTW, your L2 problem you mentioned in the other post and looking at your photo espec...

Suggests a base to emitter short on Q1. I see the JYE diagram shows 0.3V. You need to pull Q1 out and do either a continuity check with an analogue VOM or a Digital multimeter that can test transistors. You might want to check you have a real DSO138 by checking your traces as described in the forum....

You are still not telling me what instrument you are measuring the -27.41Volts with.

You seem to be missing your -5V supply (AV-).

Do more measurements around Q1 and U4.

If you get really stuck I tried replacing the whole switcher and -5V regulator with this http://www.jyetech.com/forum/viewtopic.php?f=18&t=505

AV- - 0v
AV+ - 5.00v
+3.3v - 3.31v
+5v - 5.00v

Well, they don't look right! Have you mixed up your - and + signs? AV- should be -5V, etc

What are you measuring TP25 with?

Do you get -5V on TP26?

With a 12V supply I wouldn't expect more than -12V at this point. What are you measuring it with? Also, I would suggest trying to reduce the supply down to 9-9.5V.

Do you get -5V on TP26?

Before putting another unit in I would check that the +5V (TP24) and -5V (TP26) supplies are correct. Also, try to check them right on the IC PCB pads.

Orientation, double check with the TI datasheet