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Odd output from Elenco XP-15K Power Supply
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tomherrick:
OK, now it's getting weird...  DMM on VDC, neg to P4, pos to cathode side of D1, I get a momentary reading that differs each time then is replaced with the reading you see below. Momentary readings were 15.45, 17.24, 11.72, and 17.50 on D1. Momentary readings on D3 were 14.89, 19.82, and 19.21. All were shown for less than a second then the DMM display shows "1  .  ".  Golly, I hope that helps...   :-//

rstofer:
That measurement on pin 3 of the LM317 is very wrong.  Unfortunately, troubleshooting beyond this point may require some disassembly and that is often problematic on single sided boards.  The pad tends to lift off the board.

If I were making the tests, I would remove the LM317 and then check the Input and Adjust pads.  The Adjust won't change because it doesn't have the feedback from the output voltage but it should be about -1.4VDC.  And the Input should be about 24VDC.

Before we worry about regulating, we need to get the Input level correct and we need to know that we have that negative rail for the Adjust circuit.

SolderWick is your friend and I would use the wider variety.  Make sure there is plenty of solder on the pad before you apply the wick.  I know, counterintuitive.  If you have to buy SolderWick, buy some paste flux as well.  Put that over the solderball on the pad to increase the amount of flux beyond what SolderWick supplies.

Were it mine, I would cut the leads off the LM317 and remove them one by one.  Less chance of damage that way.  Of course, I would need to buy a couple of spare LM317s...  I would absolutely do it by cutting the leads.  I have destroyed too many pads...

https://www.digikey.com/products/en/soldering-desoldering-rework-products/desoldering-braid-wick-pumps/265?k=solder+wick&k=&pkeyword=solder+wick&sv=0&v=473&pv1698=6&sf=0&FV=ffe00109&quantity=&ColumnSort=0&page=1&pageSize=25

I would use the 0.1" braid for this operation.

https://www.digikey.com/products/en/soldering-desoldering-rework-products/flux-flux-remover/266?k=paste+flux&k=&pkeyword=paste+flux&sv=0&v=473&pv183=3336&pv771=256&pv771=259&sf=0&FV=ffe0010a&quantity=&ColumnSort=0&page=1&pageSize=25

LM317

https://www.digikey.com/product-detail/en/texas-instruments/LM317T-LF01/LM317T-LF01-ND/3640769
rstofer:
Since the voltage should be 24VDC, I would expect it to overload a 20V scale.
rf+tech:
A less invasive technique would be to take a few more measurements. Up to this point, all DC measurements have been from the back side of the negative output binding post. And there appears to be a suspect solder joint where the wire from this binding post connects to the board.

The next step would be to measure DC voltage across C1 (2200 uF), with the DMM black lead to the striped side of C1 and red lead to the other side of C1.

Set the DMM to the 200 VDC range.
tomherrick:
These will have to wait a bit. I have a long list of tasks that I haven't gotten to yet. This 12V power source was simply intended for use with a marine GPS chartplotter to load maps and waypoints. This has turned into a stumbling block rather than an interesting intellectual exercise.

That said, I hope to get back to it soon and thank everyone for their thoughtful input. Very nice of you all.

I'll be back soon to pick up where we left off...
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