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Thread: Kaypro 4/83 voltages...

  1. #1

    Default Kaypro 4/83 voltages...

    I pulled the main board and the power supply. Both look really clean. I budged/seated all the socketed IC's on the mainboard just to freshen up the connections. The voltages are 4.95V, 11.5V, -12.2V. I have the issue where the screen width will move slightly when the drives turn on - but the voltages are the same drives on or off. I was having a horizontal jitteriness in the display, but it hasn't happened so far since putting it back together, so I'd like to think that might be no longer an issue.

    Is the -11.5V ok? I saw there was a multiturn pot on the power supply, but I'm not sure what voltage it might change...

    I used a LCR meter on the power supply and it was coming up with a resistance for the bank of red caps in the middle (16V 2200uf + 2200uF + 1000uF), or it was coming up with a very large amount like 14.34mF. Same thing with the two caps in the corner, both are 40V and around 1000uF in parallel. One came up 25 ohms and the other 3mF or something. I think my LCR meter tries to autodetect what it is connected to and below a certain threshold it assumes resistance...

    The screen width issue is more of a bounce, it bounces skinnier and then returns back to where it was when the motors start up, but not when they stop.

  2. #2

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    The jitter issue is still present. It started as 4 rows and spread over the whole screen and then went away. I read in the micro cornucopia something about jitter, but it was on a big board. Maybe the Kaypro has a similar thing? Does anyone know what IC's might be part of it? I could add more bypass to them if it would help... It starts and stops sitting there doing nothing...

  3. #3

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    I would check the video cable and plug under the main board. also i had issues with the 4 pin plug on left back as well. maybe a re-cap of the video board and psu will fix it if not done, i do that first off as i have 4 kaypro's. a 2x and 3 x 10's

  4. #4
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,238

    Default

    Alan,
    That last posting jogged my memory. Check to see if your Video Board has a 5 or 8 Pin Plug.
    The Motherboard has a round Pins sticking up that the Video Plug pushes down onto. Remove the
    Plug, and get some fine crocus cloth and polish up and down the pins. I had to do that on mine to get a
    good video signal. I had intermittent problems with a connection on those pins. My Pins had a light bluish
    tint to them that the crocus cloth removed.

    I think I posted here on VCF about that problem. Sure did, and I got a lot of some what negative postings
    about the REAL problem from the VCF experts. I had the same type problem on my 2003 Chevy Silverado.
    http://www.vcfed.org/forum/showthrea...t=crocus+cloth

    Have a look, it may save you some time.

    Larry
    Last edited by ldkraemer; November 18th, 2019 at 06:43 PM. Reason: added url

  5. #5

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    I rocked the long connector going to the video board back and forth a few times and removed/reattached it. So far no problem so maybe it was a bad connection... We'll see!

  6. #6
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,238

    Default

    Alan,
    Did you notice any of the shiny metal pins that had a bluish tint on them? If not, then only time will tell.

    Thanks.

    Larry

  7. #7

    Default

    Hi Larry,

    No, but I'm color blind so I might not even notice. I was hoping rocking the display board connector fixed the horizontal video jitter issue, but it didn't, that comes back from time to time. I'll try to look at them up close with a magnifier.

    I did manage to desolder the soldered in IC's from U66, U86, and U87 and add sockets for these three. I did the drive fix on U87 by bending out pins 1/9 and then making the 1-6 and 12-15 jumpers. This did not change my drive B: problem (it will work one minute, but not the next) - Not sure what to try with B: next, maybe I'll pull it and try to rw-wet all the solder connections on its control board to see if that makes a difference.

    I'm going to do the speed mod next (which is why I also socketed U66 and U86).

    Thanks,

    Alan

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