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Kaypro 4

Computers in Collection

General Info


Supply is an Astec, and has those infernal input capacitors that like to go up in smoke after 40 years. I need to replace them…

Floppy Images

Converting .IMD files to .RAW (.IMA) files for use with the Gotek:



Hirose ‎TM1R-616P44-35S-150M‎ is a potential replacement keyboard-side connector.

Kaypro 4, serial 89298

Kaypro 4 powered on and waiting for a floppy

Kaypro 4 running a Space Invaders clone game

No modem or real-time clock. This rules out it being a “4-84”. Full-height drives suggests this is actually a “IV” or a “4-83” or “IV-83” (depending on who’s offering the name). TODO: Check that the floppy drives are DSDD.


Acquired from cupajoe123@eBay in October of 2017. Picked up in Bend, Oregon in December of 2017, if I recall correctly.

Logic Board

Kaypro 4 logic board

TODO: Better, complete photo of the logic board.

Manufacturer Kaypro
Part “PC81-240A”
Serial “18235” (hand-etched on PCB)
BIOS ROM U47 “81-232”
Character ROM U43 “81-146”
Sockets Most complex ICs (RAM, ROM, CPU, I/O chips), a few standard logic ICs
Date Codes early/mid-1983

All the ICs on the board are standard, off-the-shelf components, unlike later Kaypros that had one or two Kaypro-custom ICs.

Maintenance Log

Display took fifteen seconds to warm up. Pixels of text were clearly being scanned out, but were all stacked up as a single line along the middle of the screen. The line had the appearance that it was wrapping around. The display hardware was making a considerable whining noise.

I spent a bunch of time pulling socketed parts and cleaning the IC pins with Scotchbrite and dusting out the sockets with a stiff little brush. No change in the display. Probing around the circuit board, there’s clearly life, as the data and address buses and clocks were all bumping around as I’d expect. At some point, I found one IC with a pin tucked underneath, not in the socket, which I fixed.

I located a wooden chopstick and poked the potentiometers on the CRT circuit board, and after poking the H-hold (?) pot, the whining immediately stopped and the screen stopped rolling about. The image was crystal clear.

Now time to clean and lube the floppy drives and hook them back up to power and data. Too bad I don’t have any floppies.


Disassembled and scrubbed/cleaned everything. (Re-?)lubed the floppy drives.

Kaypro 4 disassembled, CRT and labeled hardware

Kaypro 4 disassembled, complete

Cleaned the CRT as best as possible using brush and Windex-like cleaner (not on the deflection coils though). Cleaned HV terminal with alcohol. Repacked with dielectric grease.

Kaypro 4 CRT yoke LCR test


Replaced keyboard-side connector with new part, crimped and soldered on using existing parts. Here’s the broken jack, with the correct wiring visible, more or less:

Kaypro 4 keyboard-side broken jack, wiring harness