Kaypro / 8K EPROM Modification / Part 3


4K to 8K EPROM Adapter Kit

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When I first opened my Kaypro 10 I was a little surprised about the modification on the mainboard. But after I had spent some time looking at the different BIOS, I knew what had happened here.

This modification is necessary if you want or need to use an 8K (2764) instead of a 4K (2732) BIOS or EPROM. Now that I knew what had happened here, I quickly found out on the internet. This modification is described in detail in the Advent TurboROM manual.

The TurboROM for the Kaypro 10 is an 8K (2764) EPROM. The TurboROM can be plugged into all Kaypro 10s except for the early versions. Early Kaypro 10s can be distinguished by the position of the 50 conductor (approximately 2 1/2" wide) ribbon cable. The ribbon cable attaches near the middle of the main circuit board on early Kaypro 10s, not to the edge of the main circuit board as in later model Kaypro 10s.

This appendix details how to modify the early Kaypro 10s to accept the TurboROM, in the event that the TurboROM Adapter Kit is not available. This adapter is available from Advent Products, Inc., to perform this same modification without soldering or permanently modifying the main board. When using the TurboROM Adapter Kit to install the TurboROM in a Kaypro 10, the 16 pin IC, also contained in the Adapter Kit, is not used.

The Adapter Kit provides a jumper wire for connecting pin 2 of the TurboROM to pin 2 of the Z80 CPU which is the 40 pin IC at position U28. If the TurboROM Adapter Kit is not available, the instructions below will duplicate the installation of the adapter.

See also „Sharkonwheels“ at VCF.

My adapter is homemade. The amazing thing here is that no TurboROM was used at all, but the usual "81-277-A / 1.9E(F)", which is actually a 4K BIOS.

Restore the Kaypro 10 to it's original condition? Just remove the adapter kit, burn a new 4K BIOS and insert it.

Kaypro 10 with modification
Kaypro 10 with 2764/2732 apapter kit

Modification: Wiring between pins 1, 28, 27, and 26 of the new BIOS 28-pin socket (U42). This will give +5v to these pins. Connect pin 2 (A12) with pin 2 of the Z80 CPU.

Kaypro 10 with modification
Replacing M2732A with M2764A
Z80 CPU (A12 address signal)

So far, so good. The modification described above is understandable. But now there is another one, which I do not understand as a non-professional. Following is an excerpt from the "KayPLUS ROM Upgrade" manual. Numbers 1 to 5 are the same as the previous instruction, but numbers 6 and 7 are different.

from KayPLUS ROM Upgrade
from KayPLUS ROM Upgrade

Pin 10 of the 74LS157 multiplexer is a data input line.

74LS157 (l1d data signal)

In my two Kaypro 10 I use the 81-277-A BIOS in U42 and the 81-278-A "character generator" EPROM in U26.

A little hint!

Because I sometimes have problems with the „old“ UV-EPROMs with the burning, I figured, just test an EEPROM from ATMEL. I also use this - with adapter - in my IBM 5150.

And what can I say, it works flawlessly and the burning/erasing is incredibly fast! Just use an ATMEL AT28C64B.

And how do you get a 4K BIOS into an 8K EPROM? Nothing is easier than that; just double it.

C:\> COPY 4K.BIN /B + 4K.BIN /B 8K.BIN /B

My series about the: Kaypro

--> Go to Part 4: Formatting a Kaypro 10 hard disk