Adapter board that allows use of regular EPROMS on Amiga 500 Rev 5 boards A500 boards with revision 6 and higher don't have these problems and don't need this adapter.
To be able to use regular 27C400 or 27C800 EPROMS on Amiga 500 Rev 5 boards, you will need to lift out pin 31 on the chip, connecting it to VCC and instead connect pin 31 in the socket to pin 1 on the chip. If that wasn't enough there are compatibility problems between some EPROMS and some machines/CPUs which requires pull-up resistors on the address pins. This simple adapter board solves both problems. It re-routes the EPROM pins and has place for two optional resistor nets.
Diag ROM installed on a Rev 5 board
| Component | Pcs | Name | Comment |
|---|---|---|---|
| 100nF ceramic capacitor | 1 | C1 | |
| 4.7k resistor array | 1 | RN1, RN2 | 9 resistor arry (10SIP). 10k is probably OK as well |
| DIL-40 socket | 1 | EPROM socket for top side | |
| 20-pin header | 2 | Round machined pin headers for bottom side (mates with motherboard) |
Retro Ninja