Ambika power irregularity

Discontinued products Ambika
#1

I’m reading incorrect voltages on all but the blue point during power test.

Green: +0.01
Yellow: -0.18
Red: -0.25
Blue: -7.97

I’m experienced in working with analog electronics, and its my suspicion that one of the voltage regulators is ruined, but I thought I would get the advice of others before replacing parts.

Thanks for any advice…

#2

Are you using an AC adapter? NOT an AC to DC adapter!

#3

9volt AC.

#4

Could you post the voltages you measure on each of the 3 terminals of the 4 regulators?

And could you please post a photo of the power supply section of your board? Looks like one of the rectifying diodes is soldered backwards.

#5

Checked all the diodes, unless the pcb doesn’t match the DIY ref. page.

7908ACT A: 0; B: -8.81; C: -7.97
LM9407: A: 0.02; B: 0; C: 0
Same for 7805ACT

#6

I really appreciate the quick replies.

#7

And now near the power connector?

Could you also send the reference (or a photo) of your power adapter?

#8

Your 7908 is working fine. But the LM2940 and 7805 get no input voltage.
Either the diode D2 is soldered backwards (has to show to the opposite direction of D1) or there is a cold solder joint at D2.
If you have doublechecked D2 and all is right, then it is most likely a wrong power adapter.