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Kaypro 2x no horizontal or vertical sync


Sep 13, 2022
Hello all I picked up some Kaypro equipment recently and I’m currently working on a 2x. The issue I’m having is no display. I started looking at the crt board and found no high voltage checked all the transistors and caps on the board along with the traces and everything looked good I replaced several electrolytic just to be safe, I was told that the high voltage is controlled by the horizontal portion of the board. I then pulled the o scope and fluke meter out. Theres 5 volts dc on the vertical but no signal. The video and horizontal are at zero volts and no signal. I then changed out the video ram and installed a blank character prom to do the 9, screen fill. Still nothing. Could a bad 6545 video controller stop this? Now I don’t think the computer is running. The voltages are good but the drives don’t seek. Would a bad z80 processor or bad boot prom stop the whole machine? This is my first cpm machine and I got a whole bunch of disks with it. I have the technical manual downloaded all ic’s were pulled and reseated one at a time and the board traces and solder joints were checked. Thanks all!


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I'm pretty sure the 6545 does not power-up in a working state (producing video), so if the Z80 cannot run the instructions in the ROM, the 6545 won't be setup and enabled to produce video. So, it could be anything along that line, including the custom-LSI chip attached to the 6545. In fact, the other custom-LSI chip used for DRAM control could also be involved. Maybe start checking that you're getting a good 4MHz clock on the CPU, and then work outwards from there. There are ways to check the CPU as well, like forcing NOP and watching address lines.
That’s what I was going to do next Is Che the the processor. I have signals at the the clock crystals themselves. Well I’m slowly working my way back
Well I remembered that I have a pk-232 modem used for ham radio applications and it has a z80 in it so I swapped them and we have activity! The cpu was dead!


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That's always nice to find it was a faulty part and to have a spare on hand. I am still trying to get more software onto my 2x.
Well this machine was stored improperly but at least I have a good start point. It came with a lot of the original kaypro branded master disks. Going to order more z80’s seeing as I have several pieces of equipment that run them now. I’ll give updates on this machine on this thread