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Need help with OTI037 EGA/VGA card

A

albr

Member
Joined
Jun 29, 2015
Messages
21
Location
St.-Petersburg, Russia
Hello!

I've got 8Bit ISA EGA/VGA card based on OTI037C chip for my XT computer:

oak-vga-8bit.jpg

Trying to use it with my LCD VGA monitor I get black screen with "Signal out of range" message.

I've tried to find any information about this card (jumper settings etc) in the Internet and found two similar cards.
One is 8bit but have only VGA (15pin) connector, the second one is 16bit and have EGA(9pin) and VGA (15pin) connectors (like mine).
Obviously mine is something third... I've tried all 16 combinations of switches with the same "Out of range" signal.

Can anybody help me solve this problem or share any information about such card?

Thank you for any help/advice,
Alexander.
 
Try all four switches in the OFF position.
Did you wait some time? At startup it seems to put out 15kHz for a short time.

Some switch settings:
BIOS 2.15

SW4-3-2-1
0000 -> VGA monochrome, grayscales, character problems with system BIOS
0001+ -> VGA color
0101 -> EGA
0110 -> CGA
0111 -> Hercules
1000 -> as 0000
1001 -> VGA color
1010 -> EGA signal, detects as VGA, many video modes broken
1011 -> MDA signal, detects as VGA, many video modes broken
1100 -> VGA color
1101 -> VGA color
1110 -> VGA mono, MDA attributes, characters compatible
1111 -> VGA color

I may not have found some other differences, especially with the VGA color entries.
 
Last edited:
Thank you for your reply.
I've tried this card with CRT monitor, the same result.
My CRT monitor shows actual H and V frequencies of signal when it is out of range. I've found combination of switches when Vsync was 50Hz and Hsync was 29.5KHz, but valid range is 20-120KHz. Probably this card is not compatible with my monitors :(
 
Additional info that might be of some use:

I had picked one of these from the trash and found it not functional. Symptoms:
- system gives 'no video' beep codes
- system boots
- the card is putting out 25kHz/35Hz which is unsuitable for monitors
- the BIOS chip works fine in another card of similar type

Later I put it together with the working card in the same system. The broken card put out a blue screen, the working one showed black.

Had the idea to replace the video DAC. Unsoldered with hot air at 260°C (card lying on an old plate heater), tried the unsoldered part in another video card. It gave incorrect colors. Well, could still be an incompatibility. Back to the broken card, placed a socket and put a new old DAC taken from storage 'cooling chamber of the slaughterhouse'. The card is now working.

It appears that video BIOS does some hardware checks and aborts when it finds an issue. It leaves the CRTC generating these incorrect frequencies that were used for its self test.
 
Looks similar to my case. Recently I get another one, it's working fine, but first does not despite jumpers settings. Most probably first card is really broken and works in EGA mode?
I have no DAC to replace, so I'll just store this card somewhere just for a case :)

Thank you very much,
Alexander
 
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