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Kaypro 4/84 crt

K

kurt_kayger

Experienced Member
Joined
Dec 25, 2020
Messages
61
Location
Germany
Hi,

for days I have had a problem with the Kaypro 4/84 board 81-194.
The CRT display changes the quality after approx. 2 seconds.
Green background stripes appear.
The longer the Kaypro is used, the better the picture.
It is not a fault with the brightness controller.
My second Kaypro has the same problem. Only here do the stripes disappear again after a while.

Does anyone know the phenomenon and can give a tip.

I like the Kaypros and I don't want to lose them.

greeting
Kurt
 

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Looks like the video "black level" is too high (contrast too low). I recall being able to see that same thing on a "new" 2X if the brightness was set too high. I would adjust the brightness so that the background "bloom" just disappeared. Haven't studied the video circuitry, but I suspect some components are just getting old and causing low contrast and/or high black level. If adjusting brightness down so that background disappears results in the foreground being too dim, you probably are going to need to look for faded components (I don't recall if there are any internal adjustments to make). I always preferred and low brightness setting, and worked in subdued light conditions, so never had a problem.

I suspect whatever it is will be totally fixable, but I don't have the video electronics expertise to advise much more.
 
Hi Doug,
thank you for the answer.

Yes, the SUB Bright setting must be changed.
There is a rotary potentiometer on the control electronics of the Kaypro 4/84.

Everything OK again. Excellent!

Kurt
 
Last edited:
What Is the Manufacture of the Video Board? If it is Elston I have the Schematic for it, that I bought some 20-30 years ago.

Larry
 
Hi,
I can't find out.
The board says PW 385 or G89.

It is the KAYPRO 4/84 (S / N116 916) produced for Europe.

greeting Kaypro_Video.jpg
Kurt
 
iHello Larry.

thanks for the information.

My KAYPRO 4/84 is now working again.
I changed the PRE-BRIGHT setting on the board.

Kurt
 
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