4A ROM Replacement

[Willsy]

How feasible would it be to replace the 4A ROMs with either:

 

• a set of EPROMs (does the 4A custom ROMs match with a particular ROM pin-out?);
• a small board with EPROMs or Flash chips?

 

[atrax27407]

EPROMs can be used to replace the even and odd console ROMs. If memory serves, they are TMS2532s.

[Tursi]

As usual, the answer is on Thierry's page

 

http://www.unige.ch/medecine/nouspikel/ti99/eeproms.htm#console

[repetto74]

I would like also to replace one of the two ROMS because it is faulty and TI99/4A won't boot. So as far as I understood Thierry's page the original ROM must be kept into the console and a piggyback is required for the replacement? What about if the ROM is faulty? Is this going to work?

[Tursi]

For a faulty ROM I'd prefer to desolder and replace it.. it's hard to predict what it's going to do.

[matthew180]

The hardest part is desoldering the original ROMs. Once you remove them and install sockets, your are open to any options you want, i.e. replace with EPROMs, make a PCB to allow using SRAM that is loaded on boot, shadow RAM that can page out the ROMs, etc. If the ROMs were already in sockets I think this kind of thing would be a populate upgrade.

[repetto74]

I have desoldered the faulty rom and soldered a socket. Now anyone can tell me how to replace this chip with an Eprom? Which one and what file to program in ? The TI99/4A is a PAL version. I would like to do things simple and just replace the faulty ROM then I may consider later the PCB upgrades as explained .

 

The ROM is the one sitting on the left of the two scratchpad Ram IC's and labelled :

8228

C71077

 

Many thanks for your help.:-)

Edited October 19, 2017 by repetto74