Eudimorphodon
Veteran Member
There's a listing that's been running for a while on eBay offering a lot of five "AS-IS" OTI077 ISA VGA cards for a little less than $20. I wanted a VGA card to check out if one would work in my homemade Tandy 1000 EX/HX expansion system, and since that lot of five was less than what most people wanted for one card I took a chance. I'm curious if anyone else here has bought one of these same lots, and if so how it worked out.
After the cards arrived I randomly pulled one and tried it in the HX, and so far as I can tell it worked 100%. (There are a couple little compatibility things I've found but I think they're Tandy 1000 related quirks, not a problem with the card.) It's been a few weeks, and just today I've finally gotten around to feeling like I should test the other four. Here's the results:
Of the five cards three worked. Two worked 100% out of the bag, while one of them was recognized by the machine but I got a blinking blank screen instead of proper video. Upon inspection I found that the socketed RAMDAC chip on that card was partially unseated in the socket. I reseated it and the board seems to be working fine. (I tested each card in several graphics modes, including VGA modes 12h and 13h, GEOS' OAK 800x600 SVGA driver, and EGA mode 0Dh.)
Two of the cards didn't work at all. The Tandy 1000 HX BIOS probes for a VGA card as part of its startup routine; if you leave a CGA monitor attached, as I had, with a VGA card inserted when you power up you'll see the "Memory Size = 640k" message appear for a few seconds on the onboard video before it's disabled and control handed off to VGA. With the two non-working cards plugged in the machine never disables the built-in video and just continues booting in TGA mode.
All the cards have the same PCB. The cards that worked and didn't work clustered into two groups that differed slightly in how they were populated. Here's a picture of an example from each side-by-side:
The "bad" cards have socketed BIOS ROMs instead of soldered-on, and they have a different brand RAMDAC. (The bad ones have a "MUSIC TR9C1710-66PCA", the good have a "KDA0476BCN-66"). The "good" ones also have an inline resistor pack populated between the DAC and BIOS ROMs, while the bad ones don't.
I was initially going to open this thread to see if anyone might have an idea off the top of their head if that resistor pack might have something to do with 8/16 bus width detection or similar, but after I started typing an obvious "wait a minute" popped into my head; the Tandy BIOS probably determines if a VGA is present by looking for a VGA BIOS, and the "bad" cards have socketed ROM chips.... so, yeah. I've reseated the ROMs and now both "bad" cards seem to work. Have one in the machine now running a diagnostic loop, and if it works after a few power cycles I'll do the same with the other one.
Anyway, if anyone else here has bought some of these I'm curious what you got. And if you happen to *need* a VGA card, well, if my experience is any guide these might be worth taking a chance on.
After the cards arrived I randomly pulled one and tried it in the HX, and so far as I can tell it worked 100%. (There are a couple little compatibility things I've found but I think they're Tandy 1000 related quirks, not a problem with the card.) It's been a few weeks, and just today I've finally gotten around to feeling like I should test the other four. Here's the results:
Of the five cards three worked. Two worked 100% out of the bag, while one of them was recognized by the machine but I got a blinking blank screen instead of proper video. Upon inspection I found that the socketed RAMDAC chip on that card was partially unseated in the socket. I reseated it and the board seems to be working fine. (I tested each card in several graphics modes, including VGA modes 12h and 13h, GEOS' OAK 800x600 SVGA driver, and EGA mode 0Dh.)
Two of the cards didn't work at all. The Tandy 1000 HX BIOS probes for a VGA card as part of its startup routine; if you leave a CGA monitor attached, as I had, with a VGA card inserted when you power up you'll see the "Memory Size = 640k" message appear for a few seconds on the onboard video before it's disabled and control handed off to VGA. With the two non-working cards plugged in the machine never disables the built-in video and just continues booting in TGA mode.
All the cards have the same PCB. The cards that worked and didn't work clustered into two groups that differed slightly in how they were populated. Here's a picture of an example from each side-by-side:
The "bad" cards have socketed BIOS ROMs instead of soldered-on, and they have a different brand RAMDAC. (The bad ones have a "MUSIC TR9C1710-66PCA", the good have a "KDA0476BCN-66"). The "good" ones also have an inline resistor pack populated between the DAC and BIOS ROMs, while the bad ones don't.
I was initially going to open this thread to see if anyone might have an idea off the top of their head if that resistor pack might have something to do with 8/16 bus width detection or similar, but after I started typing an obvious "wait a minute" popped into my head; the Tandy BIOS probably determines if a VGA is present by looking for a VGA BIOS, and the "bad" cards have socketed ROM chips.... so, yeah. I've reseated the ROMs and now both "bad" cards seem to work. Have one in the machine now running a diagnostic loop, and if it works after a few power cycles I'll do the same with the other one.
Anyway, if anyone else here has bought some of these I'm curious what you got. And if you happen to *need* a VGA card, well, if my experience is any guide these might be worth taking a chance on.