820-2101-A replaced GPU, boot chime wont go pass apple logo

[protocold]

I have replaced defective GPU with a new one and machine boot up with chime but it wont go pass apple logo when the bar is around 50% it will just reboot.

I tried to boot linux and it wont go into anything with graphic but somehow pure text mode seems to be ok.

Where should I start looking?

 

[2informaticos]

Seems that machine fails when tries to load graphic driver.
Possibly bad chip, or solders...

 

[protocold]

maybe i killed the chip during the replacement... what's the max temperature that I should use on these GPU chips?

 

[2informaticos]

Temperatures differ for leaded and lead-free solder.
Also the rework stations are not equals.
Be aware, the temperature setting in station menu, is not the same as the value achived by motherboard.

I cannot give you a value for a particular station model.
You should practice in scrap boards, when configure your station.

 

[piernov]

Also be sure you got a good chip. Must have white underfill (not dark) and datecode > 0830 at least, model number G84-603-A2. Preferably "128-bit" memory bus, "64-bit" should still work if it's a good chip but it'll be limited to 128MB VRAM (it's probably a remarked G84-53-A2). Most chips on the market are remarked garbage (but the underfill color cannot lie on these GPUs at least).

 

[protocold]

Thanks piernov. Is it true that all G84-603-A2 have white underfill?

I have got supposedly new G84-603-A2 with white underfill and those chips are green, I presumably killed them as they turned brown after I put them on the board so I am really puzzled by the temperature.

 

[piernov]

I think all the G84-603-A2 should have the good underfill yes (the white one).
Chip shouldn't get discolored too much when soldering. If it is, it indeed may have gotten overheated.
As 2informaticos said, profile will vary between rework stations but also between boards, so you have to calibrate it on your own using donor boards.
This BGA replacement is an easy one to do with proper equipment, but you can't get it right on the first try, needs some prior experience with BGA rework.
That said, temperature at the chip shouldn't go as high as 245°C, and even that is a bit too much. And of course it shouldn't stay for several minutes near reflow temperature.
If you have a cheap garbage rework station, I'd recommend reballing the chips with leaded solder before soldering.