A bit of an update on this incase its useful to someone...

I followed the general flow of trouble shooting that others seem to suggest.

- No open resistors or missing capacitors.
- No obvious broken or dry solder joints on the fbi chip or tmu chips. I reflowed these to be sure as the solder was a bit dark and oxidized but no change.
- I found a copy of the steam engine demo that some one from youtube wrote and used to test the fbi chip. This looked fine so pointed towards the tmu's again.
- No obvious broken or dry solder joints on any of the tmu ram.
- Removed all 8 tmu ram chips off the back side of the card, to downgrade it into an 8mb voodoo2 and hopefully halve the amount of memory that has issues, and repeated the donut demo test. Problems as above still present, suggesting the first 2mb of tmu ram was the problem area, not the second 2mb.
- Removed all 8 tmu ram chips from the front side of the card. Cleaned them in ultrasonic cleaner to get rid of remaining flux and tested the ram in a pci s3 trio 64v2/dx video card. I found it best to only change one chip at a time, instead of pairs, as if it didnt detect the extra ram it was hard to tell which chip was the problem one. 3 ram chips appear faulty as the s3 trio doesnt like them and only reports 1mb of memory, not 2mb.

Have ordered some more ram chips, but coming from aliexpress who knows what will actually turn up? Others seem to have had luck.

Later this week when i get some time i will test the memory from the back side, using the same s3 trio card, and make sure thats ok before fitting it to the front side. If it works fine as an 8mb configuration then that proves that the faulty memory is indeed the issue. If not, more trouble shooting is required.

Another update..

Today i checked all of the tmu ram that was removed from the back side of the card in the s3 trio and they all tested ok. I have soldered them on the front side of the card and it now runs fine as an 8mb configuration. The problems in tye 3dfx splash screen are gone and the textures and background in the donut demo are fixed now too.

Once the new ram chips arrive ill see how they go, but assume that will work fine and bring it up to 12mb again.

Next im tempted to have a crack at doubling the tmu ram to 8mb and making it a 20mb voodoo2. Ill have to put some thought into how to achieve this without stacking the ram chips as i feel thats a bit messy and asking for trouble with how close together the chips are. Has any one else actually done it? Ive not managed to find much info about it other than it is doable and supported.

Only seen it done on a voodoo1 4 mb where stacking made it a working 8mb card.

Don't know if it works on a voodoo2..

It's not possible to upgrade a V2 like this. The TMU/FBI have no extra pins.

sdz wrote on 2023-04-30, 20:59:

It's not possible to upgrade a V2 like this. The TMU/FBI have no extra pins.

Theres a voodoo2 datasheet floating about that suggests each tmu is capable of having 2, 4, 8 and 16mb of memory. That said, it does note that this is not available in the alpha version of the chipset, so maybe it was never actually implemented. The fbi is only mentioned to support 4mb.

Ive just had a bit of a look and the Ras signal is usee for bank selecting. Ras for bank 0 come from pin 129 on the tmu, and Ras for bank 1 comes from pin 128 on the tmu. Other adjacent pins definately have connections, which is where id expect to be looking, this fits in with 4mb being the limit. Has anyone got a dead card with a tmu removed that they can send a righ res picture of? If theres any unconnected pins we could probe them for activity. I dont really fancy removing a tmu just to look underneath it though.

Yeah, the datasheet is preliminary, it even mention SGRAM support IIRC.

http://sdz-mods.com/wp-content/uploads/2023/0 … /7d-scaled.jpeg
http://sdz-mods.com/wp-content/uploads/2023/0 … 0068-scaled.jpg

It mentioned sgram and sdram but noted they were not available in the alpha version. I guess these features never made it into the final voodoo2 chips and was probably implimented in future chips on later cards.

Wow, thanks heaps for that!

Looks like every pin is connected to something. Id expect any extra unused outputs to be left floating rather than tied high or low through a resistor so i guess that confirms that. Pitty.

I sanded, scanned all the layers, traced everything and reversed the schematic a few years ago. Any "extra" pins are either tied to GND or VCC, but removing the TMU and measuring directly its pins confirms that all those GND and VCC pins are internally connected to each other.
Sorry to dissapoint.

Oh wow, thats an epic effort!

Another update... The new memory chips from aliexpress arrived. They appear consistent with the old chips in terms of look and the printing on them. All same date code and the printing didnt rub off with iso alcohol, so hopefully they are real chips. They worked fine in the s3 trio too. I soldered them on to the voodoo2 and everything seems good. So i think thats probably now a success.

Well done on the successful repair. I've had no trouble yet with these ram chips from Aliexpress.
Good that You tested first in a card with empty sockets.