No AHT when I hold down D

There are differing opinions on that. It is soldered onto the Logic Board, so it's not what Apple would do. They would just replace the entire board. But--only as a total guess--you might find someone who is willing to do it. I'm not certain it's even possible and, if so, same caveat about finding someone extremely skilled in doing this. And no idea how much the part would be. But that way it might be considerably less expensive than from Apple.

Don't know if Apple still has this, but there used to a one fee to fix everything, which might actually be less expensive than the cost for a Logic Board replacement.

There are some independents around, but I wouldn't know whom to recommend or trust with this.

Steve Over wrote:

Ok, I got hold of ASD 3S132 and made a bootable USB flash-drive.

The test gets to "Loading Video Controller devices" and then the computer just shuts off.

I'm pretty sure I have a faulty GPU, so I guess we are talking about a new logic board if Apple fixes it? can anyone guess a total price that Apple would charge?

I think that's the wrong ASD. Could be Must be why it's shutting down at that point. For the mid-2010s I think you want ASD 3S140. Again, be very careful where you get this from.

>>it's down to me to fix; I have repaired GPU faults on many PC laptop and even a few MacBooks. But before I tear this machine to pieces I would like to run Apple's diagnostics.

>>so I might be able to replace just the graphics card?

Is this yours ? http://www.ifixit.com/Guide/iMac+Intel+21.5-Inch+EMC+2389+GPU+Card+Replacement/6 272

if so, the card can be replaced, albeit with some effort.

AHT will sometimes fail to initialise with faulty memory or GPU.

51 Steps. Not for someone without considerable experience. I wouldn't go near it. But if the OP doesn't want to venture it, might find someone, maybe even an AASP, who would do it.

And since the OP used the wrong ASD, we can't even be sure it's the GPU yet.

Am I right in thinking that the bigger the number the newer the ASD is?

AFAIK, yes.

so 3S142 and 3S156 would be fine?

No. AFAIK you need the 3S140. There may sometimes be some overlapping, but I don't think in this case that's so.

The EMC # should be on the bottom of the foot.

Best of luck with that - was it one where the gpu is on a separate card ?.

Yeah, good luck. A reflow won't help if it's the chip, though. In that case, a new card.

iMac (21.5-inch Mid 2010)

AHT came on one of two install discs that shipped with the machine, Pop the appropriate one in and then restart holding down the D key. See http://support.apple.com/kb/ht1509 for details.

Splendid 🙂 & well done.

Does AHT or ASD work now ?

Impressive work!