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Can't get matching +/- voltages (help!)
Posted: Sep 11th, '15, 23:35
by agitprop
I built the power section, and it shows the positive voltages normally, at +5V and +14.7V respectively, but I can't the negative voltage to match. I am currently seeing -16.9V.
I am using a Triad WAU16-1000 16VAC wall-wart PSU, but the first time I tested the power section, I mistakenly used a 15V DC source. I'm wondering if that was sufficient to have compromised the negative side of the power section.
Has anyone seen this happen before? Any ideas for how to prosecute a fix?
Re: Can't get matching +/- voltages (help!)
Posted: Sep 11th, '15, 23:47
by ikke
The negative rail needs a little load and will go down to 15V.
viewtopic.php?f=16&t=373&p=2318&hilit=n ... tage#p2318
Re: Can't get matching +/- voltages (help!)
Posted: Sep 12th, '15, 01:43
by agitprop
Thank you so much, ikke! This is a godsend. Have a great weekend!
Re: Can't get matching +/- voltages (help!)
Posted: Sep 12th, '15, 14:22
by ikke
You're welcome!
Re: Can't get matching +/- voltages (help!)
Posted: Sep 16th, '15, 00:03
by agitprop
I tried a 2.1K resistor and 3.3K resistor, between Ground and -15V pads, and my voltages definitely got closer to each other relatively, but the absolutely values are a bit screwy now.
For example, here is what I see with a 3.3K resistor:
+5V pad is showing +5.6V
+15V pad is showing +16.17V
-15V pad is showing -16.65V
I'm guessing I just haven't put sufficient load between ground and negative. What resistor value worked well for you?
Thanks again!
ikke wrote:You're welcome!
Re: Can't get matching +/- voltages (help!)
Posted: Sep 17th, '15, 00:10
by agitprop
I put away my shitty Mastech multimeter and fired up an amazing old HP 3456A voltmeter, and. . . surprise: the voltages are close to being exactly right.
Thanks so much to ikke!
Re: Can't get matching +/- voltages (help!)
Posted: Sep 17th, '15, 12:22
by ikke
Nice to see you got it sorted out!
Having a look at your second measurements (when you placed the resistor between -15V and Ground), they all seem to be 10% out of range so i don't think your multi meter sucks but suffers of a low battery.
I bet if you refresh the battery from that Mastech meter, it will show about the same Voltages as your HP 3456A multi meter.
Re: Can't get matching +/- voltages (help!)
Posted: Sep 18th, '15, 20:29
by agitprop
Oh, that's great advice! I just figured I had put the thing through so much misery that it had finally checked out.
EDIT: Battery replaced and Herr Mastech is back on fleek
ikke wrote:Nice to see you got it sorted out!
Having a look at your second measurements (when you placed the resistor between -15V and Ground), they all seem to be 10% out of range so i don't think your multi meter sucks but suffers of a low battery.
I bet if you refresh the battery from that Mastech meter, it will show about the same Voltages as your HP 3456A multi meter.