Firecracker 24 modification?

[brett71]

Hi all,

I recently obtained a Firecracker 24 V2.0 board that seems to have some sort of modification done to it. Would anyone have any idea what was done or why?

I've attached pictures. It appears that 3 chips on the upper edge of the card have been linked into a custom-made PCB with a chip on it and a few other components as potentiometers. The main chip is an MB40978P-SH, which I looked up as a "DAC, 3-Channel, 8-Bit RGB D/A Converter". This revision of the board also does not have a 15-pin VGA plug, but has a 15-pin plug of some other type which I don't recognize.

I've looked up the Firecracker 24 on the BBOAH, and the picture there is of a V2.1 board and it seems like that one has a single chip in the same general position as the board I have. Did someone try to upgrade the board from a V2.0 to V2.1?

Can anyone tell me what's going on with this, or if it's a known mod?

Thanks!

[MiaM]

Once upon a time some equipment used a DA15 dsub connector (15 pins, two rows, same spacing as the connectors used for mouse/joystick, serial, parallell, floppy, rgb and scsi on Amigas) for VGA style signals. I assume they did this due to the DE15 connector (often incorrectly refered as HD15) were kind of expensive and rare in the early days unless you were a customer about as big as IBM were.

Not sure if there is a standard pinout but you should be able to ohm out which pins are ground and then you can usually see which three pins seem to follow a similar path on the PCB - those will be the RGB signals. Then you need to find the two sync signals. Any kind of measurement instrument like preferable an oscilloscope would of course help a lot here. The RGB output pins won't suffer any damage if they are conencted to a sync input. However there is a slight risk of damages if you hook up a sync output to an r/g/b input.

Hopefully someone chimes in with some more useful information.

[brett71]

I actually have no use for this card, I happened to get it along with another purchase, so I'll likely just put it up for sale. But first, I want to know what I'm dealing with here, and how to properly describe it.

[shaf]

The MB40978P-SH Part is a 3 Channel 8 bit RGB to D/A Converter so my guess is the this is the Optional SVHS Module.

[chb]

As the MB40978P-SH is exactly the same chip as on the 2.1 revision pictured here, and your expansion board fits into three identical-looking sockets, my guess is that they replaced three separate DACs with a single, 3-Channel one after finishing the first board design. So probably some prototype revision. Those hand-written "Auto" and "Pointer" labels and black tape stickers on the EPROMs add to that impression.