junky Jetway P4MDPT board

[zunasthegreat]

Re: junky Jetway P4MDPT board

Great tips there thanks a lot. I recently tried to repair a very bizzare LC-8460BTX PSU that mad a horrible buzz sound, the amount of cost savings the maker did was just nuts. PSU had in total 3 filtering caps for 12V/3.3V/5V voltages, one each and half the pcb was empty. The 12V cap gave a reading of 35pF ...

[momaka]

Re: junky Jetway P4MDPT board

KZG Job done ... 6.3V 1500uf and 3x Nichicon 1500uf 16V. Mainboard posts normal so far.

Nice work!

Keep an eye on those KZG caps, though. Generally, they've had a lot less issues with newer batches than older ones (from like 2005-2007), but they still may fail occasionally. By far, their biggest enemy seems to be sitting on the shelf without seeing any voltage / use. So the more you use that motherboard, probably the better off they will likely be.

On that note, I just recently posted about a socket 775 ASUS P5GC-MX motherboard with KZG caps, where pretty much every KZG failed. Of course, note that this is an older motherboard from 2006-2007 era, when KZG really was problematic, so that's probably why so many of them failed. Newer KZG seem to be doing OK for the most part and I tend to leave them alone (but still keep an eye on them when there's a chance! )

The old GSC 1500uf caps are a mystery, 6.3V ones show very high Vloss on meter ~5% but their capacity is epic at around ~2600uf.

Ah, classic GSC / Evercon failure mode before they start bulging. Looks like you caught them right on time!

The high capacitance means their electrolyte is breaking down the aluminum foil layer and increasing the capacitance at the expense of decreasing the maximum voltage they can tolerate. As a result, their internal leakage current also goes up, making the cap more "lossy", especially when operated at voltages closer to the cap's rating. Eventually, this will keep getting worse until the cap "just loses it" one day and partially begins to conduct/short out, making it bulge and then leak.

So again, you caught them on time.

Though IME, GSC / Evercon tend to break down rather slowly over time, so they sometimes allow the device to continue working for quite a bit before they finally fail completely.

On a related note, the GSC caps from the Jetway N2PAP-LITE motherboard I linked to above in post #2 have all started failing in the same exact way - extremely high capacitance and high Vloss... though none have bulged yet. I've used them as test caps in a few low-stress circuits, and they are just about adequate for that - but never going to use them permanently in anything again, because they will get worse further and further over time.

That being said, if a capacitor is showing a capacitance that is more than 20-25% higher than what the cap is rated for, then suspect a possible near future failure. The old UCC KZG also actually fail in this manner (as do many other unstable caps.) So checking the capacitance of loose caps in your stock from time to time can sometimes tell you if any cap may be failure pending to happen.

[zunasthegreat]

Re: junky Jetway P4MDPT board

KZG Job done ... 6.3V 1500uf and 3x Nichicon 1500uf 16V. Mainboard posts normal so far. The old GSC 1500uf caps are a mystery, 6.3V ones show very high Vloss on meter ~5% but their capacity is epic at around ~2600uf.

[momaka]

Re: junky Jetway P4MDPT board

IDK, I think I've seen poly caps with high Vloss like that before. I guess just connect that cap to a 2-2.5V source and see if it holds voltage for, say, over 10 minutes. If yes, it's probably not as leaky as the meter shows. I honestly don't pay too much attention to Vloss on my meter, as some of my lytic caps (and I think a few polies too) easily show 3-4%.

If you have a small low-voltage DC motor (like out of a CD drive eject mechanism or tape player or similar), you can also connect the charged cap across it to see if the motor spins for an instant. If it does, then the ESR and capacitance are probably reading correct and cap should be OK.

[zunasthegreat]

Re: junky Jetway P4MDPT board

For lowside VRM cap bank I'll mix solid 820uf 2.5V (sepc series) + some nichicon 2200uf 6.3V. The 16V ones will be replaced with Nichicon HD's 1500uf 16V.

*My cheap tester shows Vloss above ~5% on the NCC solid 680uf 2.5V caps.
Crappy reading or whole batch of semi-working caps ? Other caps on tester show the usual 0.5-1% Vloss so I guess its not tester error.

[momaka]

Re: junky Jetway P4MDPT board

Btw I still have around a Lelon-Modded Soltek P4 board that still goes strong from ~2012.

Nice.
A lot of older boards didn't care as much about low-ESR caps (particularly early Pentium 4 boards and ones older than that.)

The arrangement of those caps look similar to an ECS P4VXASD2+ I have. That one came stock with OST RLX and all caps are still doing OK, despite the board abusing the VRM high-side caps with a ton of heat. Then again, that board doesn't care about low-ESR caps either. Its CPU VRM is one of those inefficient 2-phase designs, done with Schottky diodes as the free-wheeling devices and a KA7500 IC for PWM control (read; relatively slow switching frequency.) Oh, and the funniest part is that it uses the 5V rail to power the CPU instead of 12V. The board is quite good for abusing/testing the 5V rail on old PSUs.

[zunasthegreat]

Re: junky Jetway P4MDPT board

That jetway on the link looks so OP with proper caps. I'm awaiting some nichicon HD's to arrive so I'll consider mix and max like u said. Btw I still have around a Lelon-Modded Soltek P4 board that still goes strong from ~2012.

[momaka]

Re: junky Jetway P4MDPT board

Sorry for hijacking OP. Will the NCC PSA series 2.5V 680uf Solidcap work for the VRM area on a junky Jetway P4MDPT board ?

Looking at pictures of the board online... Most likely, I'd say the answer is YES.

Given how many caps it has around the CPU, converting it to all-polymer will still probably give good enough capacity on the CPU VRM low side. This can be important for older boards (and especially budget ones like PC Chips and ECS) that used relatively low VRM switching frequency. But your board's CPU VRM appears as relatively medium frequency design, so solid/poly caps should work OK.

That said, you don't have to go all solid or all wet electrolytic caps. You can mix and match too to get both higher capacitance and better ESR in the circuit. That's what I did with my Jetway N2PAP Lite, detailed here:
https://www.badcaps.net/forum/showthread.php?t=63041

In case of your board, you can probably do like 2/3b of the caps on the CPU VRM low side as polymers, and 1/3 or so wet electrolytic with high capacitance.

Also, as "junky" as this Jetway may appear, notice they used a through-hole socket for the CPU. That actually makes the board quite bullet-proof, especially when subjected to the horrible warping from the stock Intel heatsink mounting mechanism.

[zunasthegreat]

Sorry for hijacking OP. Will the NCC PSA series 2.5V 680uf Solidcap work for the VRM area on a junky Jetway P4MDPT board ? Originals are "Evercom" 1500uf 6.3V and are crap, 16V Highside VRM has same Evercom 16V 1500uf that I'm gonna replace with some Nichicon HD series @ 2200uf.