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Kaypro 4/84 wont take kaylplus or turbo ROM, only works with 24 pin orginal roms

VERAULT

VERAULT

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So this thread is a spin off from the freHD for use on Kaypro thread. I was burning some kayplus roms to install on my kaypro 4/84 when none of the roms worked. When I tried them in another of my 4/84 computers the ROMS I made work fine. The only differences I can see on the boards are the one in question has u75 marked as SPARE and unpopulated. While the one that works with the new ROMS has u75 populated with a 74LS10. The kaypro that doesnt work also has several bodges and bridges under the board which look factory to me.

Pin 2 of the rom socket and pin 2 of the z80 have continuity. Can someone lend some advice as to why it wont take a 28 pin rom when the silkscreen on the board shows both sizes.
Mick
 
Not specifically, but since 24 and 28 pin ROMs are not pin compatible, there must be either jumper settings on the board, or else you will have to convert it manually.
 
On my other ksypro 4/84 i pop out the 24 pin rom and pop in the 28 pin eprom i burned and it works fine. They both halve silk screening on the same socket for both size eproms.
 
Might be helpful to get the Kaypro part numbers for the board(s) that work and the board(s) that don't. Kaypro did a lot of mixing-matching, so probably need to ensure both of your 4/84s have the same mainboard.

The 2732 and 2764 EPROMs *are* actually pin-compatible, when you anchor them both on the bottom. Because pins are numbered from the top, the pin numbers change. However, there is no need for jumpers or rewiring to switch between 2732 and 2764 on properly-wired 28-pin sockets (as long as the 24-pin EPROM is registered to the bottom of the socket). There is a need for jumpering between 2716 and 2732 (both 24-pin EPROMs).
 
The thing is both of these boards are listed as "universal boards". Both are almost exactly the same except on the board in trouble.. U75 was an unpopulated 16 pin "socket" ( no socket just holes filled with solder) while u75 on the working board has a 74ls74 14 pin ic in a socket. Otherwise they are a spot on match..
 
I'm guessing this thread took a left turn, assuming that the ROM itself was not working instead of the code in the ROM was not working. I seem to recall some after-market ROMs for the kaypro depended on hardware modifications, so perhaps this one needs whatever mod was done to your working board. Are there instructions with the ROM that describe a hardware mod?
 
durgadas311 said:
I'm guessing this thread took a left turn, assuming that the ROM itself was not working instead of the code in the ROM was not working. I seem to recall some after-market ROMs for the kaypro depended on hardware modifications, so perhaps this one needs whatever mod was done to your working board. Are there instructions with the ROM that describe a hardware mod?
Click to expand...

It is possible sure, however I have had these kaypros for years and they are both bone stock. I just burned the ROMS myself (kayplus and advent turbo). Both had the original 24 pin roms with version 81-292 bios. But only one of them will utilize the new bios. Does that make more sense?
 
So, the parts list for mainboard 81-292 (2/84, 2X) shows U75 as a 74LS74. Same is true for the 4/84 mainboard 81-184. In fact, all the later mainboards show U75. The schematics suggest that U75 is integral to the video, so not sure how a system can operate without U75. Clearly, the two boards are not identical. Can't explain it, you may have to track down what really is different between the two boards. Actually checking the board part numbers might be required. And revisions. If U75 does not even have a socket on one of your boards, it must be very different.
 
Well, clearly there must be some differences. I couldnt tell you if the board was ever swapped when it belonged to the orignal owner. I cant find any actual board numbers as both boards have "assy 81-______" with nothing writeen on the board. Which is odd since both boards have hand written serial numbers.
 
Now that I've been burned myself while trying to install a TurboROM in one of my K10s, I'm wondering if you checked the Vcc wiring to the socket. The 24-pin EPROMs get +5V on their pin 24 (aligns with pin 26 of a 28-pin part), while 28-pin (e.g. 2764) want it on pin 28. I never noticed that my original TurboROM had a small jumper between 26 and 28. Of course, the one I picked from my parts bin did not. Took more time than I care to admit before the light went on and I realized the EPROM was not receiving any power :). Have you checked your non-working board with a meter to see if there's +5V on pin 28 of the socket?
 
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Thats not a bad assumption. I can certsinly give it a try after the holiday. I pretty much got discouraged and shelved the whole thing.
 
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