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Electronics => Repair => Topic started by: MPereira on May 01, 2019, 04:48:43 pm

Title: RX 480 MOSFET (MDU1511) weird short?
Post by: MPereira on May 01, 2019, 04:48:43 pm

Hey guys!

I've recently bought a dead RX480. It doesn't have the 12v on the motherboard side shorted, and neither on the PSU side, the fusistors seem to be ok as well. The thing is that all the mosfets on the card are shorted on the Drain and the Source. (All the Gate's seem to be fine) The mosfets are MDU1511 and MDU1514, is this supposed to be normal? The drain shorted to the negative on the card?? There are a lot of smd capacitors that are shorted on the card aswell. I've tried to input 3v on the 12v line of the pci (I know it is an awfull lot) and I couldn't find anything warming up.

There is a small burnt area on the graphic card. (Attached pic) And a couple capacitores out of place close to the pci (I suppose these are not the problem, because the graphics card should at least boot on the 8x pci slot).

What do you guys think? is the short on the drain supposed to happen? What should I test next? If I have a short should it be present on the input pins?

Thanks in advance

(https://i.imgur.com/JZ6Wbwy.jpg)
(https://i.imgur.com/VbDKzat.jpg)

Title: Re: RX 480 MOSFET (MDU1511) weird short?
Post by: PKTKS on May 01, 2019, 06:00:42 pm

Hard to say on loose terms.

But VRMs depend exclusively on the supervisor chipsets used

And... in all cases (integrated or serial coupled doublers/drivers) the
HIGH SIDE and LOW SIDE MOSFETS can not be "shorted"
if so they are dead.

CAPS can not be shorted as well as if so they will dead short the MOSFETS.

But ... along the road .. a damaged GPU will dead short the whole chain

Remember ..we are dealing with pure beasts which power up a 100W to 200W/300KHz
to 500KHz at least  device.  Driving low as 1V we have peaks of 100A or in excess of 200A.
That will be loosely split in phases ...

Enough to fire in flames and build holes.

and the only safe way to tell for sure is removing and testing .. even
after that removing and testing the supervisors - e.g. you remove the chip
to test if the shorts are still there, even the PCB layer may be damaged
and/or being repaired and faulty again

be safe
Paul