Hi SirNickity
I wasn't so much thinking of testing digital signals on custom ASICs. From the sort of repair I've done for example on miniature SMD circuitry on diverse devices such as Android and MAG IPTV boxes, or for that matter SATA Hard Drive controller boards, It is generally more a matter of testing the things that can be checked such as all the various power rails, oscillators, reset signals etc. if a Processor has the correct power, has a clock and isn't held in reset and it still isn't working then probably I can't fix it.
But at least half the time I find for example short circuit SMD capacitors, short circuit or otherwise faulty Buck regulators, blown or short circuit power FETS, duff electrolytics, common faulty components such as HDD motor controller IC, duff PWM controllers and duff Gamma correction ICs on LED/LCD TCON boards..... that sort of thing. For those components you can almost always find the datasheet/pinout and can always rework them with hot air, some good solder skills and some decent bench magnification.
From what info I can glean so far regards about video cards is that they are fairly simple devices with a few sections - at lease the more modern ones. Basically they seem to be 50% buck regulator circuits, and the other 50% made up from RAM, the GPU itself, a Bios (ROM), possibly some 'glue logic' to interface with the PCI-e or AGP slot to and some circuitry to monitor errors such as temperature or over current. That seems to be about it.
So now i am wondering how often that circuitry (especially the buck regulators) is failing compared to how often it is the GPU. Power supply isn't so hard to diagnose/repair and even RAM should be at least 'doable'.
Older cards i would think are less integrated, for example having separate RamDAC instead of integrated in the GPU.
Many tutorials seem to say that the only thing that ever goes wrong with a video card is the BGA reflow soldering. So they are easy to repair - throw it in the oven that will fix it. Don't even bother to see if the correct supply voltages are present to the GPU and RAM first, why would you even want to bother to check for something simple like that. Remove the plastic parts and GPU heatsink first? Nahhh....
Oh and put it at 200C for 20 mins. That is hot enough to melt solder....
Well actually it isn't... lead free solder which is what you will find on your GPU doesn't even melt until 220C. Personally I find those tutorials just plain stupid. 😲
So anyone here been repairing video cards and have some idea of the proportion of actual GPU failures to the proportion of other more easily fixed problems?