A12 v1.4 i got used doesn't seem to work...
Posted: Sat Dec 18, 2010 7:49 pmI got an old A12 v1.4 used. The guy knew it didn't work and gave me a good deal, so I didn't get screwed.
Anyway, it had a number of problems:
The trim pot had been abused and was half broken off. I replaced that.
There was no R21 - literally it just wasn't there! I replaced it with another 100k that I had from another project. I verified that R20 is also 100k. Measured them as well... got 100k and 99k.
After fixing all that, when I use the original SC25 (that may or may not be working) or a Purple opamp from another working A12, I can't change the output voltage. No matter what I change R19 to, it stays 3 something volts. Both cases, the regulators are hot to the touch (too hot really).
Anything else I should look for before coughing up the $175?
thanks,
Scott
Anyway, it had a number of problems:
The trim pot had been abused and was half broken off. I replaced that.
There was no R21 - literally it just wasn't there! I replaced it with another 100k that I had from another project. I verified that R20 is also 100k. Measured them as well... got 100k and 99k.
After fixing all that, when I use the original SC25 (that may or may not be working) or a Purple opamp from another working A12, I can't change the output voltage. No matter what I change R19 to, it stays 3 something volts. Both cases, the regulators are hot to the touch (too hot really).
Anything else I should look for before coughing up the $175?
thanks,
Scott