Why Does My ATI Mobility Radeon 7500 Chip Get So Hot?

[singbad]

Hi,
I've got a couple of dead T30 system boards with ATI Mobility Radeon 7500 chips that get hot. Some more, some less but all much more than the ones in working systems.

I wonder if it's due to an internal failure of the Radeon or if there's a common external cause like overload or short circuits.

Expert opinions are welcome.

Best regards,
singbad

[SMA]

When chips that are designed to operate from more than one supply voltage, is operated with one or more, but not all supply voltages present,
then it is normal behaviour that they can get warm.

There are chip, where a specific combination of supply voltages present/not present will damage the chip, but those cases
are usually protected electronically so that the chip will not be damaged.

I wouldn't worry about a warm GPU chip on a faulty board. Instead, I would use it as an indication of what is wrong with the
board. The first thing I would suspect would be a faulty voltage regulator.

[singbad]

I need a working system board so I went through the ones with the hot Radeons hoping I could save one. I found all are missing the main CPU voltage (VCCCPUCORE). This means the CPU voltage converter circuit is not working.

It's a buck converter made up of 2 parallel dual CMOS bridges driven by an Analog Devices ADP3203 2-Phase IMVP-II and IMVP-III Core Controller for Mobile CPUs. IBM's circuit is pretty close to AD's data sheet example except there's no diodes. They use synchronous rectification instead. Does anybody know how to troubleshoot this kind of circuitry?

I don't have an oscilloscope, I can only check DC voltages.

Any advice?

[singbad]

I've checked the MOSFETs, re-soldered the inductivities, checked the supply voltages of the ADP3203 controller and the auxiliary chips. I did not unsolder and check the capacitors - will I have to?