No video on Compaq HP 6735b, what is the best method for GPU reflow?

Compaq HP 6735b, num lock/caps lock lights flashing 5 times and no video. From what Ive read, a reflow of the GPU is indicated. Remove the board and cook it.  There are quite a few videos on youtube. I have a MHT 750 heat gun which at 750° F is too hot I think. Then theres always the oven, 10 minutes @ 400° F. Either way, a lot more than just the GPU is going to get very hot. Does anyone have any hints or clues on this procedure other than "dont do it"? The laptop is a doorstop now, I cant make it any worse. There is no critical data on it.

The manual says "Thermal pads are used on the Northbridge chip and the section of the heat sink that services it. Thermal paste is used on the processor and the section of the heat sink that services it." Are the thermal pads necessary vs just paste?
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i used a heatgun, which i fixed 10-15 cm above the board
if you want to know at what point the solder melts, i put a bottle capsule with some solder on it on top of the video chip

personally, i let the gun run for about 10 minutes
i repaired 4 HP DV9500 like this
disciple_of_chim-chimAuthor Commented:
Excellent! What temp did you set the gun for? My heat gun's lowest setting is 750°F - isnt that too hot?
As nobus mentioned, just move the gun further away and check with solder. Mount the gun at distance where it just still melts the solder. The further away, the less hot the surface will get. I also recommend using flux fluid around the chip, that helps the solder to distribute itself properly. Cover the parts of the board around the chip with aluminum foil, so that those parts don't heat up too much.

The oven trick is generally a bad idea, as there are usually parts on the board that don't take too nicely to heat, and also, most boards have parts soldered on both sides, and as an oven heats evenly, it's likely that those parts that are on the bottom of the board will desolder and fall off.
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my gun is a simple paint stripper, and has no setting
disciple_of_chim-chimAuthor Commented:
Using the sample solder as a guide sounds like a good idea but what type of solder do I use, or does it make a difference?
There isn't much difference in the melting point of the different solder.
disciple_of_chim-chimAuthor Commented:
Well, theres something wrong with this picture - I put a piece of .032  63% tin/37% lead, rosin core solder on a penny and and mounted my heat gun 1 inch above it. I started at coolest (750°F) for at least 5 minutes, no melt.  I went to 1000°F, still no melt. Maybe its the gun, I dont have a temp probe. The wood it was sitting on was charring but I think it should have ignited long before 750°F.
i can assure you my setup works fine.
if you can strip paint with it, it should work, certainly at a distance of 1"
the solder you used - is that norrmal electronics solder?
if in doubt, i practice first on an old or bad electronics equipment
Lead has as far as I know been banned from solder several years ago. Most electronic solder melts at between 200°C and 220°C. What that is in Fahrenheit I have no idea (and since that measurement should have been banned, like lead in solder, a long time ago, I refuse to do the conversion myself...).
disciple_of_chim-chimAuthor Commented:
I taped the intake vents closed, wrapped it in bubble pack and towels and started it. The first time, no luck. Tried it again and voilà- it got hot enough to melt the solder, video restored. We'll see how long it lasts

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glad it's working again
disciple_of_chim-chimAuthor Commented:
Though helpful, the other comments were not what resolved the problem. What I chose to do did resolve the problem.
while it works now - i still have doubts on "the soldering" job that was done this way
i hope it keeps up - but never saw any reference to a gpu reflow like this
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