CPU doesn't appear to be receiving power from 4+4pin post water damage

[Matthew Frank]

I had a terrible day yesterday and decided to do some maintenance using water and I payed the price. I'm trying to narrow down the issue to try to limit what I replace. I don't have replacement parts to swap out for testing purposes anymore.

The system runs as long as the CPU's EATX12v is not supplied power by the 4+4 from my PSU. The 4+4 connectors all read 12v when checked with a multimeter.

With the 4+4's connected the unit power cycles - up for a second, then down, then up, then down - and the CPU_LED light is on.

1) Is there a way I can check or identify if its the connection on the motherboard that's bad? I'm guessing not, unless I'm familiar with electronics/soldering/etc., right?

2) If the 4+4 and the 20/24 and molex connectors from the PSU all read the right voltages it's a safe bet that the PSU is fine and I'm looking at replacing MOBO/CPU, correct?

3) My MOBO is a LGA 1156 - discontinued, and from my quick reading 1156 processors are not compatible with LGA 1155 boards - so even if the CPU is somehow good but the board connections have a short from water damage, I have to replace both.

I'm in a weird spot where I have to assume both CPU and MOBO are bad. If I buy another 1156 (discontinued) board and drop the CPU in and the CPU is bad, then I have to try to buy another (discontinued) processor...

But, it would be nice to assume just the MOBO needs replacing...

Suggestions?

 

[Matthew Frank]

Does it behaves the same when you try to turn it on while the CPU is not installed? It should, because I think that CPU is fine. Measure the resistance on the motherboard connector for the CPU and that 24 pin one. If there is a short (few ohms) on some voltage rails (you measure +3,3V and GND, +5V and GND, +12V and GND, and so on), then the motherborad needs reparing/replacing.

UPDATE: I'm getting solid 1's :| It looks like the short is, as I suspected, right on the EATX12v. In another thread I read that PSU's *should* handle permanent shorts in a non-destructive fashion. Kinda thinking that, as you said, CPU is fine and MOBO is dead.

As you suggested - it behaves the same if I turn it on while the CPU is not installed. The fans still cycle up, then cycle down, and the CPU_LED still blinks on, then blinks off.

I'm guessing the short is in or around the connectors. I've looked for damage but I couldn't see anything with my naked eye, and I didn't smell anything.

 

[Matthew Frank]

To measure the resistance, put the multimeter dial on the omhs range (if it is not automatc, put it in to 200 ohms range, or what ever the smallest range is) or on the diode range (where it should beep if there is a short). Place the leads on the power rails of the power connector on the motherboard. For 12V rail, place one lead on the +12V pin of the connector and the other lead on one of the GND pin. Same goes for other voltage rails...

Sorry - I updated my original reply to say that I was getting straight 1's - so it looks the motherboard is bad. I haven't tested the 20/24 pin connector because, I kid you not, I can't find a single paperclip in the house to jump the PSU. I've been assuming that since the system, with everything but CPU (GPU, fans, DVD, etc.) runs and the voltages coming from the molex + 4+4 are all fine, that the mobo main power connector is likely fine as well.

If the mobo is bad, it puts me in a bad way since it's a 1156. Finding another 1156 is going to be near impossible from a major retailer, and sketchy but doable from eBay. Urgh. This sucks. Seems like I'll have to replace the mobo, and CPU along with it even if it's good.

 

[Matthew Frank]

All my resistance tests have been done without the PSU connected.

If I test the 20/24 pin connector, at 20K, I do get readings - black lead to black wire + red lead to 12v (yellow) wire gives me .12 and .11.

If I test the cpu connector with the black lead where the black wire would sit and the red lead to where the yellow 12v wire would sit, I get nothing - it just sits at 1 - on the left side of the display. I tried for all four sets. I also tested resistance by putting the black/red leads from my multimeter together, and it reads 0 or next to. In my (very) limited understanding I was thinking that 0 is what we were looking for, and 1 indicated a bad connection.