Power supply only putting out single voltage (24v) - has dual output 12v & 24v

Thread Starter

born2fly

Joined Dec 5, 2020
34
Can't figure this one out. No shorts. Dual output of 12v & 24v. No 12v out anymore only 24v. Owner says there was a nearby lightning strike. No obvious damage. This is a power supply for a Haward salt water control board. Tested everything except for rectifier, transformer and disc caps. I'm not sure how the 12v is generated. Opto's are working. I looked for a bad transistor underneath but no luck, voltage check shows aprox 2v lower on secondary side compared to similar working PSB. I am not sure how the 12v is being supplied.
 

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sagor

Joined Mar 10, 2019
786
It appears to be a switching PSU, and the 12V "could be" controlled by one of the 3 TO-220 devices near the bottom of the board in your first picture.
Depending on the load, the 12V may even be a standard 7812 regulator.
 

AlbertHall

Joined Jun 4, 2014
12,187
It appears to be a switching PSU, and the 12V "could be" controlled by one of the 3 TO-220 devices near the bottom of the board in your first picture.
Depending on the load, the 12V may even be a standard 7812 regulator.
Can you read the markings on those three devices?
 

Alec_t

Joined Sep 17, 2013
13,229
Check if the solder streak at 'A' in the pic below is short-circuiting anything; also if the solder joint at 'B' is dry or good.

PSboard.jpg
 

Dodgydave

Joined Jun 22, 2012
10,591
Can you take pictures of the To220 devices , and which terminals are the 12v and 24v?

Looking at the transformer, it has two outputs..
 

Thread Starter

born2fly

Joined Dec 5, 2020
34
Can you take pictures of the To220 devices , and which terminals are the 12v and 24v?

Looking at the transformer, it has two outputs..
Sorry for my ignorance, how can I measure the transformer outputs? Since this is AC voltage, I'm confused about the transformer outputs to the secondary side. The 12v rail is on the far left bottom in pic showing bottom of board, exits to a wired connector on top. The LM2596 was replaced just incase and the other TO-220 were tested good as did everything else on top.
 
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Thread Starter

born2fly

Joined Dec 5, 2020
34
I am still having an issue with this supply, pretty much at my wits end.o_O I have an identical working PSB that I have been using for reference as much as I can. I spent days going over the board with a fine comb, all through hole components removed for testing. I am getting 170v at the main caps. The only thing I have not done is check the transformer output, not sure how to go about that. The other question I have - Can I inject voltage( 3v-12v) at the 12v output to try to locate the faulty component without doing damage?
 
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