Video output issues on Franklin Ace 1200

[renewedgamer]

Hi, I recently acquired another Frankin Ace 1200. This one was not in working condition, but I have been able to get the system to boot, although the video output is not good at all. Very saturated reds/greens. I will post a photo when I get home tonight, but wanted to post this in the case that someone here can help.

I have debugged down to what I believe is the issue based on probing with an oscilloscope and comparing to the other working 1200 that I have.

The issue seems to be at an IC in the video area (near the "front" of the computer) the chip TBP24S10N outputs do not seem to be close to what I am seeing on the working computer.

I looked up the specs on this chip, and it seems to be a PROM. A PROM that probably has been programmed, but is now "not" programmed correctly. Does anyone know if there is a modern replacement or someone that could program an "empty" IC?

Any help would be appreciated!

-J

 

[cryu]

The TBP24S10N (aka 82S129) at U19 on the color daughterboard is indeed a four-bit PROM, and according to the 1000/1200 schematics, is a "PROM Modulator".

You can very easily rig a modern EPROM to replace it. Attached to this post is a dump of the PROM from my 1000, which should be identical.

You might be better served by removing the color board and performing the Franklin-sanctioned color modification. That's documented on page 57 of the "Franklin Service 1 of 2" PDF available on archive.org (I don't have the link at hand, but can send the PDF if you can't find it on IA).

 

[renewedgamer]

Thank you! I will give this a try over the weekend.

 

[cryu]

No worries, and good luck. If you decide to go with the color-mod route, please be aware that you need to put a 74LS51 at ZC13, in addition to adding the two capacitors, one resistor, and a transistor.