chip overheating

[ChrisBartram]

Doing final testing of several props and one with a PROP1 linked to just a PIR (p7) and 12v cylinder immediately gets VERY hot (the chip) as soon as the switch is moved to P2. Even with the PIR and cylinder disconnected it still gets very hot immediately.
Powering it with a 12V 500mA and also tried a 12V 800mA power supply same effect.
Is something defective? Did I do something dumb? Or anything I can look at; too late to order a replacement for this year so I'd like to salvage if possible. Been a while since I've played with the PROP1s so memory isn't what it used to be...
Attached a pic in case that helps.
Thanks in advance!
-Chris

[Jeff Haas]

Which chip is getting hot?  The one in the socket on the right, or the main chip on the board on the left?

I would also try taking the whole thing off your board, and having nothing connected to it at all.  There might be a short somewhere.  Then connect only the power to it and see what happens.

Then if that works, connect to the computer and see if you can get the BASIC Stamp editor to recognize the board.

[ChrisBartram]

The one in the socket on the right.
I've connected my adapter to it and the BASIC Stamp editor does recognize it lets me download/run code on it.

[Jeff Haas]

The chip on the right can be replaced easily, so it sounds like the board is OK, but it could take too long to get a new chip.  Do you have an extra relay?  You could use that to trigger the valve, and you could remove the chip from the socket and still run fine.  The valve would need another power supply on its side of the relay.

[ChrisBartram]

I didn't think the chip itself would be the cause of it overheating... but if that's the case I will look around - I probably have another one I can salvage.
Thanks!

[Jeff Haas]

I would double-check to see if anything has accidentally shorted a couple of connections.  There could be a stray bit of wire somewhere that is the issue.

[JonnyMac]

If the ULN2x03 is getting hot when the output is commanded to be off, I believe the chip is probably bad. I would seriously suggest changing the ULN. If running under load specifications, it may get a little warm, but it should never get hot.

What is the load (in W or mA at 12V) that you have connected to it?

[ChrisBartram]

I had one SY5120 12v valve connected; but also tested it in P1 power setting and with the valve disconnected and it still gets burn-your-finger hot.
I believe I have some spare chips; will have to wait till after Halloween now before I can experiment with it more though... too late for this year.

[bsnut]

I had one SY5120 12v valve connected; but also tested it in P1 power setting and with the valve disconnected and it still gets burn-your-finger hot.
I believe I have some spare chips; will have to wait till after Halloween now before I can experiment with it more though... too late for this year.

Replacing the UNL with a spare one may get you by. But, I would suggest that you use a relay control to this valve since draw less on the ULN. 

[JackMan]

What's the ma draw of that valve? Sounds like the valve may have drawn too much current thru the ULN and damaged it.

[ChrisBartram]

So tell me if you've heard this one before... lol
The supply of spare chips I had; were NOT ULNx chips... they were from some other left over project. I couldn't read the part info on the chips until I took a closeup pic with my phone then loaded it onto my PC so I could zoom in on it.

Replacing the chip with a real/correct ULNx chip solved the overheating problem.

It also turned out the PROP1 I was using had a bit of rust - in particular the power switch was stuck in the "2" position - which is where I needed it to be but it had a problem.

I tested the OUTn ports with a volt meter and discovered that when they were lit they were delivering 18-19V - instead of the full 24V coming from the power supply. I guess something in the rusted switch was adding a bit of resistance?

Had to swap out the PROP1 as well and now the prop is "firing on all cylinders" so to speak!

Appreciate the patience and suggestions!