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4K to 8K EPROM Adapter Kit
Last revision of this chapter: October 7, 2024
I EXPLICITLY WARN YOU THAT YOU MAY PERMANENTLY DESTROY YOUR HARDWARE IF YOU MAKE ANY TECHNICAL CHANGES TO IT. I DO NOT ACCEPT ANY RESPONSIBILITY OR LIABILITY WHATSOEVER IF YOU CARRY OUT MODIFICATIONS TO YOUR HARDWARE ON THE BASIS OF MY PERSONAL TECHNICAL DOCUMENTATION. IF YOU MAKE ANY MODIFICATIONS TO YOUR HARDWARE, YOU DO SO AT YOUR OWN RISK. ALWAYS ENSURE THAT THE PLUG CONNECTIONS ARE CORRECTLY SEATED. EVEN TOUCHING SENSITIVE COMPONENTS SUCH AS CPU, RAM, ... CAN CAUSE THEM TO BE IRREVOCABLY DESTROYED (ELECTROSTATIC DISCHARGE - ESD). WITH MANY OLD COMPUTER POWER SUPPLIES, VOLTAGE IS STILL APPLIED TO COMPONENTS EVEN WHEN THE SWITCH IS IN THE OFF POSITION.
!!! WARNING !!!
The Modification
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 by the previous owner. The amazing thing here is that no 8K TurboROM was used at all, but the usual 81-277-A / 1.9E(F), which is actually a 4K BIOS. This ROM has simply been doubled to 8K for the 2764 EPROM (see below).
Restore the Kaypro 10 to it's original condition? Just remove the adapter kit, burn a new 4K BIOS and insert it.
Because both the BIOS/ROM and the CPU are socketed, the modification is very easy and consists of the following steps:
- First you need a DIP/DIL IC socket with 28 and 40 pins; I use the round pin sockets here.
- Make a wiring (solder & very thin copper wire) between pins 1, 28, 27, and 26 of the new ROM 28-pin socket (U42). This will give +5v to these pins.
- Connect pin 2 (A12) of the 28-pin ROM socket with pin 2 of the 40-pin Z80 CPU socket. This requires a delicate hand, because the additional 40-pin socket still has to fit into the 40-pin IC socket on the mainboard!
- Carefully pinch PINs 1, 2, 27 and 28 (of the 28-pin ROM socket) a little, because they are overhanging in the U42 socket! Exactly at this point on the mainboard is a capacitor (C40, 104M, 12V)! Attention: Do not cause a SHORT CIRCUIT!
In my Kaypro 10 I use the 81-277-A BIOS (1.9E(F)) in U42 and the 81-278-A "character generator" EPROM in U26. I also tested the 81-302C ROM (1.9E); no problems so far.
A little hint!
Because I sometimes have problems burning the old UV-EPROMs, 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 1 : Versions
--> Go to Part 2 : Hardware
--> Go to Part 3 : 8K EPROM Modification
--> Go to Part 4 : Formatting a Hard Disk
--> Go to Part 5 : USER areas
--> Go to Part 6 : MASMENU - Master Menu
--> Go to Part 7 : Terminal
--> Go to Part 8 : KayPLUS ROM
--> Go to Part 9 : Advent TurboROM
--> Go to Part 10: Multicopy Plu*Perfect
--> Go to Part 11: Kaypro Family & Company
--> Go to Part 12: Kaypro Design Views
--> Go to Part 13: Micro Cornucopia
--> Go to Part 14: Repairing a Kaypro II
--> Go to Part 15: Kaypro Collections
--> Go to Part 16: Kaypro General
--> Go to Part 17: Kaypro Robie
--> Go to Part 18: MFM-Emulators
--> Go to Part 19: Roadrunner ROM
--> Go to Part 20: Software
--> Go to Part 21: FAQ
--> Go to Part 22: Kaypro Virtual
--> Go to Part 23: Formatting a Floppy Disk
--> Go to Part 24: ROM, EPROM
--> Go to Part 25: Kaycomp