Power Supply Help

[Dana67Dart]

I have been using a 12 v power supply to do testing on some of my MOPAR parts I make.

Today I got it out to stress test a pigtail.

To my surprise it was putting out 22 volts.

16 with a 3 amp load.

It is not a variable supply and it's max is 5 amps at 12v.

I suspect some of the components that set the voltage of the voltage regulator are bad.

I check the output for AC and nothing.

I have not opened it up yet.

Anyone have thoughts or what to look for?

 

[67Dart273]

Sum Ting Wong

I'm betting it's just a 3 pin regulator, pass transistor, and shorted. Should be, as the internet insists, "an easy fix."

If it makes you feel any better, I once had one of the better RadShi.............ack CBs with a supply that did the same thing. No idea how long it sat there before I finally noticed, LOL

 

[Dana67Dart]

Sum Ting Wong

I thought he crashed the plane

Real news report!

 

[Dana67Dart]

If it makes you feel any better, I once had one of the better RadShi.............ack CBs with a supply that did the same thing. No idea how long it sat there before I finally noticed, LOL

I used it last year to test my gauges. I have no idea if it was good then. but no damage to my gauges

 

[67Dart273]

Have you had it apart? Photo of the board/ interior?

And I have no idea, are you at all familiar with linear power supplies? I guess in this day and age it could be a "switcher." (Switching or inverter type supply)

 

[Dana67Dart]

yes

And I removed the PNP transistor and it seems to be ok. I got the expected diode voltage drops (about .6v) on the correct pins

pin side of transistor circled in red. only thing that looks iffy at all

My guess is this pot (only one on the board) can adjust the output voltage


B948 -> Silicon PNP Power Transistor 2SB948 datasheet(1/5 Pages) SAVANTIC

Found the positive output lead was loose

3904 -> a common NPN bipolar junction transistor used for general-purpose low-power amplifying or switching applications

only IC on the board
C358C -> LOW Power DUAL Operational Amplifiers

even the CAP looks good, no bulging etc

 

[67Dart273]

Maybe the zener with TU

https://www.powerelectronicsnews.com/wp-content/uploads/sites/3/2020/06/Figure-1-Op-Amp%E2%80%93Based-Voltage-Regulator.jpg?w=1024

 

[Dana67Dart]

I think I found the issue.

(don't give me **** about my radio shack multimeter)



I don't think its 15 Ohms anymore!