the3dfxdude
Experienced Member
Hi All,
I bought an IBM EGA card advertised as working, but unfortunately it does not. The screen does not display properly, with the correct DIP switches and EGA monitor. This monitor and computer works correctly on an EGA Genoa card.
I measured the vsync and hsync pins on the db9 and found 26.5 hz for vsync and 9.6 khz for hsync for the IBM card. Compared to the Genoa card, it outputs 59.6 hz and 21.8 khz.
The crystal on the IBM card is outputting a 16.6 MHz. So I narrowed things down. The sequencer chip U33 receives 16.6Mhz on pin 20 CLKIN. The sequencer outputs 8.1Mhz on pin 21 DT and 9.7 khz on pin 6 CCLK. I don't know enough of the Genoa to compare, so can someone to check the for the correct frequencies on a working IBM EGA card? I didn't bother tracing the source for vsync, but I think it's clear there is something wrong with either U33 or U32 the CTRC controller.
Can something be incorrectly causing a clock dividing?
I bought an IBM EGA card advertised as working, but unfortunately it does not. The screen does not display properly, with the correct DIP switches and EGA monitor. This monitor and computer works correctly on an EGA Genoa card.
I measured the vsync and hsync pins on the db9 and found 26.5 hz for vsync and 9.6 khz for hsync for the IBM card. Compared to the Genoa card, it outputs 59.6 hz and 21.8 khz.
The crystal on the IBM card is outputting a 16.6 MHz. So I narrowed things down. The sequencer chip U33 receives 16.6Mhz on pin 20 CLKIN. The sequencer outputs 8.1Mhz on pin 21 DT and 9.7 khz on pin 6 CCLK. I don't know enough of the Genoa to compare, so can someone to check the for the correct frequencies on a working IBM EGA card? I didn't bother tracing the source for vsync, but I think it's clear there is something wrong with either U33 or U32 the CTRC controller.
Can something be incorrectly causing a clock dividing?
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