One of the big problems of retro computing is that some parts are no longer available. Old designs sometimes use the 2708 (1K eprom) or the 2716 (2K eprom) and these are hard to get and require a old (25 Volt) eprom programmer to program. Sometimes it is just better to replace them with a later version. But the later eproms like the 2764, 27128 and 27256 are not pin compatible. Even replacing the 2708 with a 2716 can cause a big problem and defective chips. I got a question of someone who wanted to replace the 2708 of a Elektuur Junior computer board, with a 2716 eprom. I have some 2716 eproms but my eprom programmer does not go higher than 18 volt, so I could not program it. What I also had were a few 2816 5 Volt eeprom chips, these are 2716 compatible eeproms. I decided to program one of these, but with a notice that the pins should be redirected.
The eprom of the Junior computer
As you can see this old eprom uses +5, -5 and 12 volt to operate, supplying these voltages to a “modern” chip would certainly destroy them. So we need a conversation board, or we could bend out some pins and connect them with the right voltage levels using small wires.
Different pins on 2708, 2716 and 2816
As you can see there are four pins (18-21) that are different and require other levels.
The correct levels for all eproms
The main difference between the 2716 and the 2816 (according to the datasheet) is that the 2716 needs to have pin 18 to Vcc and the2816 to the Gnd. The eprom will use (select) the lowest “bank”so 0000H. The best solution for the Elektuur Junior computer seems to be a small conversion board or bend out pins 18, 19 and 21, to wire them to the correct voltage levels. With a conversion board you can easely switch the (e)eprom, with bend out pins you will need to solder to replace the (e)eprom. I have seen small adapter PCB’s on the market for those who cannot or won’t solder.