The parts nearest to it are the fan header on the other side of the board and the h/w monitor chip is very near to it, so I think it's for fan control.

Reminds me of this thread which I found while trying to do some similar repairs on a GF3 Ti200 I think? Adding a fan header to Geforce3 TI 200, help with components check needed!
Following on from that I found some MSI geforce something schematic that's a close-ish match to what you've got there:

From your picture and the shots online, we can still see "HR" which shows up when looking for it here: https://smd.yooneed.one/code4852.html
Pictures online of that part 2SA1036K online have the same font so the remaining part is likely to be that. That should mean it's potentially Q1 0 3906 on that schematic.

Looks like from looking at pics of similar V7700 cards it's the lowest pin is the red / fan power, which is great because that means things are starting to fit together for this being a PWM circuit like the schematic. Can you check if the pin that's closest to the Q805 writing is connected to ground?

I can make out HR on the transistor that's still intact but that's the one at Q804 per the silk screening. I have the broken one stuck to a piece of tape. My eye sight is being nicer to me today apparently but I can't make out HR on it. the right edge is broken off, but what I can make out at the moment looks like an underligned S followed by 1A and then it there's marks after that. I wish I had a microscope to see this, or at least that I could get a clear picture I can zoom into....

Trying to follow your response though, and I'll be clear, I'm not that type of engineer so my knowledge is a bit lacking, but I'm no dummy and I know I can work through this. That said assuming I'm following your instructions correctly, I metered the surface point for that transistor closest to the Q805 silk screen label does meter to ground, assuming the rear io backplate on the card is ground enough?

That being said, if this broken circuit is for the fan on the card, that fan has long since been removed and replaced with a vantec copper chipset cooler that uses a 3 pin connector to the motherboard. The original fan on the card died long ago. I went back to look at my testing notes on this card, but I don't see any note other than the broken transistor so now I wonder if I plugged it in and actually tested it or not. Sounds like it might be safe to test?

edit// maybe it was not the brightest thing, but I just tested the card on my abit be6 + pentium 3 with win98 I've been using to test all my AGP cards, and as far as POST goes, it displays clean all the way through boot. Windows detects the card and installs the driver, but after reboot, windows stops on a windows protection error....

I have three such cards. On two of them Q805 is marked p04 (lowercase p), the third one has a K1N instead. Good luck on restoring your card!

Thank you for checking, if the pin nearest to the Q805 text is ground (i/o bracket is great) then that confirms it's essentially the same as the schematic excerpt I've shared, there are only minor differences in resistor values and maybe differences later in the circuit.

Haha yep, I was thinking of asking "does the fan spin"? Well technically you seem to have avoided the problem already. If my understanding is correct, your Q804 is equivalent to Q1 - 3906 (PNP transistor) in that schematic excerpt. The Q805 is I'm pretty sure equivalent to Q2 - 2N7002 (N-Channel MOSFET, like NPN transistor) on that excerpt. When the PWM signal goes low, that opens the gate of Q2 which pulls the input gate of Q1 low (the N part, which is otherwise stuck high @ 12v). When that opens, the 12v power is allowed to go through Q1 and into the fan's power input (P > P).
The PWM signal allows that fan power input to turn on and off very rapidly, allowing for fan speeds slower than 12v / 100% without directly altering the voltage. Without the PWM signal being able to alter the flow of the PNP transistor's gate by pulling it to ground, the PNP transistor should never make the connection between 12v and fan voltage, so the fan shouldn't spin, or maybe it'll run at a lower speed 😀 not really worth diagnosing further.

quicknick: Thanks 😀 I see two NPN 3904 transistor codes match up with PO4 and K1N, which is great! That means the circuit should work how I'm saying and how the schematic is laid out, but uses a slightly different component, which performs the same function in the same way.

OP: since you're not using the original fan, this missing component doesn't really matter. I recommend cleaning off the remaining bits of that transistor to avoid a risk of it shorting anything, ideally with a soldering iron with a bit of flux, looks like there's not much left to worry about though..

The Windows protection error could be down to driver version, AGP drivers, all sorts. I think your testing it in this state is fine now we know you're not using the original fan. Check the board for other damaged components perhaps if you still get oddness.
You can test out the ram separately from the OS with this nice DOS-boot-disk type utility VMTCE: https://sourceforge.net/projects/vmtce/files/ Something I used extensively going through my box of scrap video cards.

okay, so on the premise that I still want to repair this circuit. some of this is over my head, but if I understand correctly, does this look like the correct part? Like I said, this is not quite my jam

https://www.digikey.ca/en/products/detail/ons … i/2N7002/244345

I have another HSF with a plug on it that looks like it fits this GPU, so I would like to swap that on as possible to have the card closer to an original configuration

I did find some information on that protection error being potentially driver/config related. I've tried driver versions 71.84 and 81.98 so far, but came across a system.ini setting for a cache setting of sorts to try out as well. I also have another Asus CUV4X board I could try it on as well so I'll have to find time to test different configurations to narrow that down or see if I can rule it out of the equation.

Also, Thanks for the tip on VMTCE, I'll take a look at that as maybe it will help me diagnose the geforce3's and 4's I have here that are problematic as well.

oh, I think I figured out what I need. I was following wrong earlier, but I found this one, seems to be the same 3904 with k1n marking as what quicknick said was on their card. I guess the same component is still available new

https://www.digikey.ca/en/products/detail/dio … 3904-7-F/815727

The jelly bean transistors and regulators are still in use to the day. Like TL341, 2N2222 etc and they are more than 40 years old design but useful.

But the newest ones are coming into use is SiC, and other new semiconductor alloys.

Well, on mention of new semiconductors, LED developments I wanted to talk about:
The last barrier for LED is true white, even warm white. Not tinted at all, real white like the incandescent lamp. Last time there was breakthrough was blue LED. Oh, I dislike the profusion of blue lights on the devices! And blue LEDs too bright at night and eye thinks white if you are not looking directly. White LEDs are currently lit by blue or UV source through a rare earth phosphorus material to add more color to mix with to look white. But your eyes and the spectrum light test tells otherwise, heavy in one band and weaker in other color bands. Makes illuminated items look wrong and light looked tinted purplish or bluish. Even cellphones still uses two white LED of different colours to make it look right.

Finding high quality white LED lamps is difficult due to this and also very difficult to find DIY LED kits that has high CRI and of good quality. This why I don't like buying cheap LED lamp bulbs and flashlights.

Cheers,