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Kaypro 4 or IV?

PostPosted: Mon Feb 11, 2013 10:11 pm
by tezza
Great machines appearing on Trade Me ... 955810.htm

This one is puzzling though. It has all the attributes of a Kaypro IV, except the case says Kaypro 4??

The Kaypro 4 has 1/2 height drives, and there are more ports in the back.

I can only surmise that either the top of the case was swapped or maybe Kaypro naming system was even more chaotic than it appears.

Either way, $100 reserve is pretty good for a classic old beast like this one.

Re: Kaypro 4 or IV?

PostPosted: Thu Feb 14, 2013 9:40 pm
by YetiSeti
Hmm, I was interested but now you point it out, I'm not sure I want a computer with an identity crisis. Although it would look nice next to my Osborne 4, except that's sitting on my work desk and I'd have to lose my work computer for it to fit (and then probably my job).

Re: Kaypro 4 or IV?

PostPosted: Sat Feb 16, 2013 8:38 am
by TRS80
I will let you know if it is a 4 or IV when I open it up.

I did see in the Kaypro column of Micro Cornucopia magazine that the swap from full height to half height was due to Tandon (who made the full height TM-100 drives) not providing good supplies due to their commitments to IBM for the PC. This made Kaypro move to other sources and there seemed to be a fair quantity of transition machines. It also talks of Kaypro II with Kaypro 4 PCBs.

Quite enjoying CP/M on my home made Z80 machine so it will be interesting to see how it differs on the Kaypro.

Re: Kaypro 4 or IV?

PostPosted: Sat Feb 16, 2013 9:56 pm
by tezza
Well done. I'm glad it's gone to one of the community on here.

Re: Kaypro 4 or IV?

PostPosted: Wed Feb 20, 2013 7:08 am
by TRS80
Picked up the machine Tuesday. It is definitely a Kaypro 4 (rather than a mix of parts) and not a 4/84 (which is what I think you have Terry).

For all intents and purposes it is a Kaypro 2 with double sided drives. 2.5Mhz Z80 (not 4Mhz like the 4/84) and no modem or real time clock (so no leaking batteries).

The power supply is the same Boschert switcher in Terry's article on smoking caps so it definitely needs the suppression caps replaced.

Otherwise it looks pretty very clean. Some minor scratches on the paint but the internals are dust free and no sign of corrosion on the metal.

Quite interesting to compare the motherboard in the Kaypro with the Tandy Model 4. The Kaypro is so much simpler (certainly based on chip count) yet does much the same job. Not sure if the Model 4 was over engineered or Kaypro were very good at cost reduced manufacturing.

Re: Kaypro 4 or IV?

PostPosted: Wed Feb 20, 2013 7:56 am
by tezza
Interesting. It sounds like the description of the 1983 Kaypro IV at least going by Wikipedia ( (section on Kaypro Model by year). Interesting that it has 4 on the case and not IV though?? Yes, my second Kaypro is the 1984 Kaypro 4 with the 4Mhz Z80, 1/2 height drives and clock.

The Kaypro's do have an elegant and straightforward single board. The TRS80 Model 4 had a BASIC in ROM which maybe lead to more board complexity? I've never had a good look at my Model 4 board actually.

Glad to hear it's in good condition. Do you have some disks for it? Does it fire up ok?

Re: Kaypro 4 or IV?

PostPosted: Wed Feb 20, 2013 10:53 am
by TRS80
Not sure if you have the Kaypro technical manual (available

The machine is the spec described as a Kaypro 4 in section 3.3. of that document.

I haven't powered it up yet... removed the power supply and will sort out the capacitors first. Saves smelling out the workshop and gives me time to make some disks. The machine didn't come with any.

>The TRS80 Model 4 had a BASIC in ROM which maybe lead to more board complexity? I've never had a good look at my Model 4 board actually.

I shouldn't imagine that Basic in ROM would have made that much difference... an extra ROM chip and some address and chip enable decoding. I could imagine that the Model III compatibility might have contributed though. Also on my Model 4's the main board is probably 30% larger than the Kaypro with the Floppy Controller and Serial Interface on separate boards.

Re: Kaypro 4 or IV?

PostPosted: Wed Feb 20, 2013 11:40 am
by tezza
Yes, you are right. Given that it is Kaypro 4 on the case and Kaypro 4 in the manual, then I conclude that it's the Wikipedia article needs some amending.

Where did the name Kaypro IV come from then? Did people over time come to call the Kaypro 4 (released in 83) the Kaypro IV to distinguish between the later variant, but it was never an official designation. In the technical manual Kaypro itself calls this the Kaypro 4. The later Kaypro 4/84 (my machine) was called 4/84 in the manual but on the case it was just plain Kaypro 4, similar to the Kaypro 4(/83).

One thing that needs to be ascertained though before diving into Wikipedia to correct the article is did Kaypro ever put out a case which had the name Kaypro IV? Maybe it did? It's not in the manual so one would think not BUT neither is the Kaypro II. In the manual they call it the Kaypro 2. On the box though it is Kaypro II. Could there be a box with Kaypro IV on it that this equivalent to the Kaypro 4 (1983) model?

Did they just switch cases 1/2 way through production of that model? The earlier case said Kaypro IV, the later one Kaypro 4?

I've had a quick look on the web but can't find an image with Kaypro IV on the case

Not that it really matters but it would be good to get a proper handle on this confusing Kaypro nomenclature.

Re: Kaypro 4 or IV?

PostPosted: Sat Mar 23, 2013 9:00 am
by TRS80
Finally got back to the Kaypro.

Replaced the caps on the power supply a few weeks ago and it sat on the workbench while other things (the TRS-80 Model 4) got sorted out.

Reinstalled the power supply and tested it with the mother board disconnected. No smoke and good voltages on the outputs.

Reinstalled the main board and on next power up was greeted with the "Kaypro - Please place your diskette into drive A".

So very pleased with that. Overall the machine is very clean internally, very little external wear and no burn on the screen. It will be interesting to see if the floppy drives work.

Time to make some boot diskettes.

On a separate note, the seller dropped past of the office earlier in the week to drop off the keyboard cable and mentioned that he had picked up the machine at an auction 7 or 8 years ago and it had sat in the corner of his office never opened. There must be a lot of interesting stuff in corners.