Repairing ..you dont repair these CPUs without some serious hardware and even then I doubt you could repair such an issue. But have you checked all the caps on the bottom to see if any are dead ?

Because if its anything other than the caps I'm pretty sure that CPU is toast and in all honesty with how cheap these CPUs are it would be easier to just grab another. (Likely cheaper too)

I also thought of the caps first. But they are all parallel and there´s 0 ohm at each of them. If one of them is the culprit it´s not easy to find.

majestyk wrote on 2022-10-18, 11:40:

I also thought of the caps first. But they are all parallel and there´s 0 ohm at each of them. If one of them is the culprit it´s not easy to find.

I'm guessing you would need some voltage on the CPU to be able to measure them, you might be able to rig something up if you had a accurate bench powersupply and a pin out diagram.

majestyk wrote on 2022-10-18, 11:04:

The seller claimed this wasn´t possible and demanded I return the CPU to China as insured mail - which - of course - exceeds the CPU´s value.

Uhm... if you bought it on eBay, that's not how it works.
If it was sold as new/used and it turned out to be dead, you just need to open a dispute and the seller WILL pay for the return shipping (otherwise he loses both the money and the item).

Anyway, I'm pretty sure that nobody bothers to repair a shorted CPU - not even Intel or AMD. They would just throw it away and give you another one. 😀

Due to the "war and pandemic situation" postage from China to Europe currently takes extremely long. While you are waiting forever for the parcel to arrive, the deadline for asking for Ebay buyer protection expires.
You probably have to call in buyer protection while the item is still in transit - so you have it in reserve in case anything is wrong with the order.

majestyk wrote on 2022-10-18, 11:04:

In summer I ordered two (mobile) Intel Core 2 Duo T7800 CPUs. When they arrived months later I had to find out one of them has a "zero Ohm" short between the Vcore and Ground-pins.

Ouch, hope the finding out didn't cause any damage. How close to zero is it?

I wonder if anybbody managed to repair such a CPU or has any idea?

Never tried, but I'd also go with removing the capacitors just in case, they can fail short. I've got a gas soldering iron where the exhaust port works as a reasonably localised hot air source for removing small SMD components. Given the CPU's probably dead already then I'd probably see about removing all the caps in one go, to save having to keep reheating the CPU for each cap. Pick them off with tweezers and place them on a bit of sticky tape in the same order so you know where they came from, in case the values are different. Once they're all off, check if the CPU still has the short. If not, then check each capacitor. It the short's still on the CPU then it's even more likely that it's dead. At which point, just for fun, could maybe see if the short can be burnt out using a bench supply on a low voltage and turning the current limit up. There was someone on here who got a FLIR camera they could use to figure out if anything was heating up.

If all else fails, you've got a supply of pins for repairing other CPUs.

majestyk wrote on 2022-10-18, 12:59:

Due to the "war and pandemic situation" postage from China to Europe currently takes extremely long. While you are waiting forever for the parcel to arrive, the deadline for asking for Ebay buyer protection expires.
You probably have to call in buyer protection while the item is still in transit - so you have it in reserve in case anything is wrong with the order.

Strange, I've had multiple orders from China in the past months and they've all arrived in 3 - 4 weeks tops (I'm also from Europe - Romania).
Anyway, if you paid using Paypal, you can open a case with them within 6 months.

snufkin wrote on 2022-10-18, 14:08:

Never tried, but I'd also go with removing the capacitors just in case, they can fail short.

I´ll probably try this with the hot air station set to a moderate temperature.
Even if one of the caps is faulty, since the CPU will not operate stable without the caps, all of them would have to be resoldered. The pitch is very fine and I´m afraid soldering contacts with just 0.5mm space between them will be a no fun operation - and we´re talking about ca. 60 caps here.

bloodem wrote on 2022-10-18, 15:58:

Strange, I've had multiple orders from China in the past months and they've all arrived in 3 - 4 weeks tops (I'm also from Europe - Romania).
Anyway, if you paid using Paypal, you can open a case with them within 6 months.

I can confirm this. I orderd a lot of components from China during the last decade and 99.9% arrived within a few weeks and the items were all 100% o.k.
One or two got lost (and refunded), one or two were defective or wrong article (and refunded).
When I tried to open a case here, the transaction could no longer be selected. I also couldn´t leave feedback. But I will check if paypal buyer protection can still help, thoough.

majestyk wrote on 2022-10-18, 16:54:

I´ll probably try this with the hot air station set to a moderate temperature.
Even if one of the caps is faulty, since the CPU will not operate stable without the caps, all of them would have to be resoldered. The pitch is very fine and I´m afraid soldering contacts with just 0.5mm space between them will be a no fun operation - and we´re talking about ca. 60 caps here.

Could try mopping up the old solder then applying solder paste and hot air to put them back? Surface tension of the molten solder (if there's enough flux) tends to pull components in to position so you don't have to be too precise. Remember soldering my first QFN package and being surprised how far I could push the chip (maybe a bit over 0.5mm) when it was floating on molten solder and it would still pull back in to position. Failing that, then yeah, a fiddly job with a fairly small tip. You may get lucky and find the short really is in the CPU so you won't have to put the caps back.

$25, paypal dispute
meanwhile buy $3 T7500, or $10 T7700 and live happily ever after 😀

I just removed half of the caps. You need nearly 500°C to melt the solder. Ironically the solder of the CPU pins melts way before any of the caps can be loosened.
Intel probably soldered the caps and pins before attaching the die on the topside.
Needless to say the short´s still there so this CPU will get binned and I´ll go with rasz_pl´s suggestion...

Interesting. High temperature solder? Or a lot of metal to heat up? I can imagine they'd want to avoid the chance of capacitors dropping off if the CPU got hot.

snufkin wrote on 2022-10-19, 11:54:

Interesting. High temperature solder? Or a lot of metal to heat up? I can imagine they'd want to avoid the chance of capacitors dropping off if the CPU got hot.

This probably was the main concern here: dropping capacitors shorting traces on the mainboard and causing major damage there.
(The whole unit heats up in no time, there´s not much matal involved.)