Changing the 2708 game roms on Zaccaria CPU type 1B1110, 1B1110/0, 1B1110/1 and 1B1110/1a.
This Zaccaria CPU board uses the obsolete and very old eproms type2708. The main difficulty is when you have to reprogram them. As they use three different tensions +5, -5 and +12 volts and most eprom programmers will not support this type of eprom. Thanks to the site Tilt-it .com the rom images are available but then we are confronted with this secondary problem.
To solve this, I worked out a solution by replacing these 2708 eproms with the 2716, or 2732.
The only thing you have to do is change two wires at connector CN7 where the wires come in to the CPU board.
This will work fine and I did try it out for myself on a "Hot Wheels" pinball. The modification is VERY easy to perform, and is fully reversible.
Who we do this
At CN7 where the CPU voltages come in; cut the red wire coming into CN7 pin 4 leaving about two inches of wire, and cut the white wire coming into pin 6 also leaving 2 inches of wire. Connect these short wires as follows,
For 5x 2716 ; the red wire from pin 4 goes to ground , you find the grounding just nearby on the outer edge of the board. And the second wire ( white) coming from pin 6 goes to +5 volts you find that on top of the diode just next to CN7. (See photo.) The cut wires coming from the power board are no longer of any use.. Just isolate them.
Here you see the connection as installed on the CPU .That is all there is to do. You can use now the 2716's in place of the 2708's now .
For 5x 2732; Connect both wires to ground ( the red a,nd the white ) You can use now 2732's in place of the 2708's.
Changing only ONE 2708.
Whenever you want or have to replace only one 2708 that can be done to. Use a 2716 in the socket and bend pins 19 and 21 upwards. Connect the pin 19 to ground and the pin 21 to +5 volts, of course the connections at CN7 are not changed (They are left in there original configuration)
If you use one 2732, again bend pins 19 and 21 upwards and connect both to ground.
Read-out of a 2708 on ANY eprom programmer!
This is possible to! The only thing you need is an old computer power supply. These gives us the needed tensions being -5 volts and +12 volts.
In the datasheet of the 2708 is recommended to put on the -5 volts before the other tensions, and to unplug the -5 volt as the last tension. So we will follow these rules in our primitive reading systhem.
My work bench power supply comes from an old PC , i added a box with banana plugs and a LED as an indicator on each tension.
To read-out the 2708 bend upwards pins 19 and 21. solder a wire at both these pins and also a wire on the pin 12 , ( pin 12 is not bended !!) solder these wires on the top of the pin. On pin 19 connect the +12 volts on pin 21 connect the -5 volts, and the ground of your extra power supply is connected at pin 12. Before plugging the 2708 in or applying the tensions put the eprom programmer settings at 2716. Now you can read out the 2708 his readings will be at 0000 to 3FF. You CANNOT program the 2708 with these connections, only read and compare.
Do not forget to apply the voltages in the correct sequence. Plug in first the - 5volt then turn on the eprom programmer ( this will apply the +5 volts )and at last p)lug in the +12 volts. If the reading is done use the reversed sequense to power down ; unplug the 12 volts, set "off" the eprom programmer , unplug the - 5 volts.
The 2708 in the programmer with his extra tensions connected.Black being ground, red =+12 volts and red = - 5 volts.
All this covers our needs regarding the Zaccaria game roms. We can read and compare their images, and if one is bad program a 2716 instead and put that in place of the 2708.
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