LM7812 and LM7912 broken? How to check

[Wolletje]

Hi,
How can I test these on the board circuit.
Its is a receiver Denon avr 1311 and the red light is blinking.
I reset the board for many times but its is death
I cannot see any strange problem on the different circuits
I read the most problems here are the regulators 12V.

I measure with the multimeter (black middle leg and red rightleft leg.
I get some numbers like +0.4 or -0.4 or counting back from xxx until zero

What do I have to read here normal and what is the right way to measure
I measure with the multi meter with V dc on 20V

Thanks,
Frits

 

[JonSnell Electronic]

On a 78 series regulator. Pin 1 = DC input. 2 = Ground. 3 = voltage out. https://www.jameco.com/jameco/products/prodds/889305.pdf

So pin1 should have more than 14v). Pin 2 zero. Pin 3 (7812) +12volts.
The 79 series are slightly different. http://www.hep.upenn.edu/SNO/daq/parts/lm7915.pdf

Pin 1 = Ground. Pin2 = input (more than -14v. Pin 3 = (7912) -12volts.

 

[MAAC0]

If the regulator is Ok and the circuit after isn't shorting / loading it, the output pins should measure their nominal regulated voltage when referenced to ground . Accept minor tolerance say +-100mV. Please note that the input pins should have a higher Voltage (min 2-3V higher) in order for the regulator to work and a minimum load also. A Led as a load (20mA) usually is enough. I would check the diode bridge and the capacitors before and after the regulators. Measure the voltage on the capacitors after the regulators.

 

[Wolletje]

Thanks!

 

[phase]

I had thought that those regulators had short circuit protection, if that’s true, then you likely have issues outside such as previously mentioned.

 

[Wolletje]

Thanks,
yes you are right
I found two burnt diodes on the PS and replaced them and also the 7812+7912 but there must be more problems because it stays yet into the death modus. I have to do more rescue work on it but it is difficult to find.