joeyoravec
Member
I'm fixing a Taito Space Invaders TVN boardset. This post shares what I've learned about modifying the Taito and Midway boardsets to use other kinds of EPROMs. I don't own a Midway boardset so I've only verified the info for Taito.
My board came with 2708 EPROMs which really stinks. 2708s are ancient and difficult to buy. 2708s require three voltages (+5, -5, +12v) so my EPROM programmer cannot read or write them. Fortunately 2708, 2716, and 2732 eproms have a similar pinout (link). By modifying pin 19, and pin 21 it's possible to substitute a more common chip like 2716 or 2732.
Both Taito and Midway board have jumpers to configure those lines. Midway published a table (link, final page) that offers settings for 18 outdated chips, but not 2716 or 2732. Taito published nothing that I could find. Taito scans on xmission are low-resolution and unreadable so use this instead (link).
Here's an explanation of the two boardsets:
You'll notice some useful settings are missing. S3 doesn't offer A10. S2 doesn't offer +5v or A11. The jumper pad is used to get a signal into the chip.... but you might have to find the signals nearby and run a longer wire. Now you have a few options:
I'll probably install the original number of 2732's, since it's so easy to get ground to those pads. But any of those work. I'm not sure if Midway has a jumper for ROM select bit 3, so you might be limited there.
I've attached a photo of my Taito TVN board with the signals. Unfortunately KLOV forum shrank the image and it's extremely difficult to read, so probe it yourself with a DMM. Here's a guide that shows you what to do on the Midway boardsets (link).
My board came with 2708 EPROMs which really stinks. 2708s are ancient and difficult to buy. 2708s require three voltages (+5, -5, +12v) so my EPROM programmer cannot read or write them. Fortunately 2708, 2716, and 2732 eproms have a similar pinout (link). By modifying pin 19, and pin 21 it's possible to substitute a more common chip like 2716 or 2732.
Both Taito and Midway board have jumpers to configure those lines. Midway published a table (link, final page) that offers settings for 18 outdated chips, but not 2716 or 2732. Taito published nothing that I could find. Taito scans on xmission are low-resolution and unreadable so use this instead (link).
Here's an explanation of the two boardsets:
Code:
Midway Taito Purpose {settings}
S1 S1 ROM pin 22 {5v, A9, GND}
S2 S2 ROM pin 21 {-5v, A10, GND}
S3 S3 ROM pin 19 {12v, 5v}
S5 S4 ROM pin 18 {5v, GND}
S6a S5 ROM select bit 0 {A9, A10, A11}
S6b S6 ROM select bit 1 {A10, A11, A12}
S6c S7 ROM select bit 2 {A11, A12, A13}
S8 ROM select bit 3 {A12, A14, GND}
You'll notice some useful settings are missing. S3 doesn't offer A10. S2 doesn't offer +5v or A11. The jumper pad is used to get a signal into the chip.... but you might have to find the signals nearby and run a longer wire. Now you have a few options:
- Use 2716 (original number): S3 Pin19=GND. S2 Pin21=+5v. Program 1k images to the bottom-half of each chip.
- Use 2716 (fewer): S3 Pin19=A10. S2 Pin21=+5v. Change ROM select to {A11, A12, A13, GND} so each ROM socket has 2k. Combine images, program 2k to each chip, and install in the correct sockets.
- Use 2732 (original number): S3 Pin19=GND. S2 Pin21=GND. Program 1k images to the bottom-quarter of each chip.
- Use 2732 (fewer): S3 Pin19=A10. S2 Pin21=A11. Change ROM select to {A12, A13, GND, GND} so each ROM socket has 4k. Combine images, program 4k to each chip, and install in the correct sockets.
I'll probably install the original number of 2732's, since it's so easy to get ground to those pads. But any of those work. I'm not sure if Midway has a jumper for ROM select bit 3, so you might be limited there.
I've attached a photo of my Taito TVN board with the signals. Unfortunately KLOV forum shrank the image and it's extremely difficult to read, so probe it yourself with a DMM. Here's a guide that shows you what to do on the Midway boardsets (link).

