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Kaypro 2x video issue

retrobits

Experienced Member
Joined
May 22, 2007
Messages
169
Location
Portland, Oregon, USA
Hi all,

I was recently gifted a pristine Kaypro 2x computer. It's a beauty, complete with manuals and disks, and it works. But it does have one minor issue. There are thin horizontal (and slightly diagonal) lines running from top to bottom of the CRT display. They are not bad enough to obscure the display but they show that something is slightly wrong.

Any thoughts on where to look first? Eventually the entire system should probably be re-capped, but that's a big job and it'll probably be a while before I can do that.

Also, there is a lithium battery on the mainboard, and it hasn't leaked. But I'm thinking I should remove it?

Thanks!

- Earl
 
Hi all,

I was recently gifted a pristine Kaypro 2x computer. It's a beauty, complete with manuals and disks, and it works. But it does have one minor issue. There are thin horizontal (and slightly diagonal) lines running from top to bottom of the CRT display. They are not bad enough to obscure the display but they show that something is slightly wrong.

Any thoughts on where to look first? Eventually the entire system should probably be re-capped, but that's a big job and it'll probably be a while before I can do that.

Also, there is a lithium battery on the mainboard, and it hasn't leaked. But I'm thinking I should remove it?

Thanks!

- Earl

Impossible to make an educated guess of the video issue without a photo of it.
 
Recapping is one thing, a far more urgent subject are those gold colored (and cracked) RIFA X2 and Y2 capacitors at the primary side of the power supply. These are just timebombs waiting to go off. Replace these as soon as possible. They will not cause immediate damage to the computer but the smoke and smell if they fail is horrible.
 
Recapping is one thing, a far more urgent subject are those gold colored (and cracked) RIFA X2 and Y2 capacitors at the primary side of the power supply. These are just timebombs waiting to go off. Replace these as soon as possible. They will not cause immediate damage to the computer but the smoke and smell if they fail is horrible.

I wouldn't be too worried about those.

The great thing about the line power supply voltage, is that it has a very low internal resistance and it can supply the 110V to a 1kW bar heater.

So if the Rifa X2 caps start to draw current and smoke, there is plenty of energy available to vaporize them and plenty of time to turn off the power before they start lighting up like Christmas tree lamps, smoking more than Humphrey Bogart on Casablanca, and stinking out the house.

You can just remove the X2 caps as they fail.

In this day and age there is little point in replacing them, when there are truckloads of SMPS's supplies running on line power (drawing current on peaks distorting the nice sine wave) and powering every appliance and energy efficiency lamp for every man and his Dog, the subtleties of keeping RF interference off the line power is well out the window by now, just throw the Rifas in the bin. You can prove this easily by trying to run a shortwave radio in most homes these days and wonder where all the RF hash is coming from.
 
So if the Rifa X2 caps start to draw current and smoke, there is plenty of energy available to vaporize them and plenty of time to turn off the power before they start lighting up like Christmas tree lamps, smoking more than Humphrey Bogart on Casablanca, and stinking out the house.
If you happen to be home, or in the room when this happens, then yes, there's enough time.
 
In my experience they tend to fail, when they do, shortly after power up.

Though many years ago I was sleeping in a room that had a Singer electric sewing machine in it. It was switched on, but not running. There was a Rifa cap in parallel with the foot pedal control, suddenly maybe around 2am, the machine started at full speed because the Rifa cap shorted out spontaneously, it was actually pretty scary and for a moment confusing as to how it happened.
 
Impossible to make an educated guess of the video issue without a photo of it.


It sounds like retrace lines to me. It can often indicate a worn CRT, where the brightness has to be turned up beyond the normal settings for a usable picture.

Sometimes it can be fixed by adjusting the "screen" control on the flyback, if it has such a control (I don't really know anything about the internals of the Kaypro).
 
Kaypro 2x video issue (pictures added)

Kaypro 2x video issue (pictures added)

Attached, please see pictures of the video issue I'm having with the Kaypro 2X.

In one picture, I've turned the brightness down all the way. You can still see the horizontal slanted lines on the screen.

In another picture, there is text on the screen from the MITE terminal program. On this screen, you can see that on lines with text, there is a horizontal streak of green on the entire line.

In the final picture, with some inverse text, some bending of the screen is also evident. (Note on this picture that the extra brightness in the middle is the camera - it doesn't look like that in person.)

EDIT: One thing I'm going to try - the Kaypro technical manual describes a brightness pot on the CRT board. It's possible that is turned up too high, causing the distortion. I'm going to try (carefully) adjusting that.

Any thoughts appreciated, and thanks again!

- Earl
20200619_195852_result.jpg20200619_200109_result.jpg20200619_200718_result.jpg
 
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Adjusting the brightness may get rid of the retrace lines, but not so sure if it will fix the other symptoms (it might).

It may be possible that all 3 symptoms are caused by one thing, so after you've tried the brightness pot, start looking around the video board and power supply for bad capacitors. They often give themselves away by leaking, bulging, or getting hot. Another cause is large components (big resistors, transformers) getting bad solder joints.

If the boards are joined by plug & socket connections, check them out too. The earlier Kaypro II was prone to that trouble.
 
Earl, Which manufacture of the Video Board do you have in that Kaypro? If it an Elston I have the
Schematic for that specific one.

Thanks.

Larry
 
I'll give an explanation of retrace lines.

In the composite video signal, on either side of the sync pulses, the level of the video voltage is defined as "black level" .The meaning of this is that the actual CRT beam current is low enough that the CRT phosphor, on the screen is not illuminated, that is, if the CRT's brightness and contrast controls are set correctly.

So , if you consider a composite video signal voltage, if all is well, then the "black level" or CRT beam current extinction level, will correspond the composite video voltage on either side of the sync pulse and the sync pulse will drive the CRT beam "blacker than black"

So, the thing to understand about the composite video signal, there are two important qualities, it's peak to peak amplitude and the DC level or DC axis that determines where the black level is.

The black level voltage around the sync pulse is also the level that corresponds to the horizontal and vertical blanking times, which is where the CRT beam is returning to start a new horizontal line or a new fields or frame of vertical scanning lines.

Therefore, in theory at least, during retrace of the CRT beam, with the contrast and brightness control set correctly, the horizontal or vertical retrace lines would not be seen, but what went wrong with this idea ? The answer is, letting the user adjust the controls.

Video Monitor makers (and TV makers) let the user adjust both the contrast and brightness control ( a analogous to a Greek senator centuries ago, saying to his friend, hey, I've got a good idea , let's let the people decide who should rule them and his friend replies ; You can't be serious, and look what happened !)

So , if you consider the situation in the VDU (video monitor) for it to be adjusted correctly, your contrast and brightness control must be set correctly.

Once the composite video signal peak to peak amplitude is set(this determines the contrast) , the brightness control should be set so the background or raster illumination, just goes black in the black level part of the signal, in the blanking and retrace time.

But let's say the user wants a brighter display , so, instictively they tun up the display brightness. This lifts the CRT's average beam current . The display gets brighter, but the black level increases, so the beam retrace lines appear during vertical flyback and appear as those tilted brighter retrace lines on the screen.This is because the video signal voltage, during vertical retrace, is not low enough to extinguish the beam.

As TV and VDU designs got better, the video black level got clamped to a fixed voltage and increases of contrast (signal peak to peak amplitude) would not shift the black level. The brightness control, then simply shifted the DC axis of the signal driving the CRT.So if the contrast control got adjusted, the black level would stay put.

Also, TV makers realised, that it would be a smarter idea to electronically blank the CRT beam, during both vertical and horizontal retrace(internal retrace blanking, as pulses applied to the CRT during retrace to extinguish the beam), so no matter how abnormally the contrast and brightness controls got set by the user, the vertical retrace lines would remain invisible.

However a lot of vintage computer VDU's don't have internal retrace blanking, so the vertical retrace lines appear a lot, if the combination of brightness and contrast controls are not correctly set.

So set the contrast control for the intensity you want, or perhaps a tad higher, then lower the brightness control until the retrace lines just disappear.
 
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Earl, Which manufacture of the Video Board do you have in that Kaypro? If it an Elston I have the
Schematic for that specific one.

Thanks.

Larry

Hi Larry,

I will be opening it up tomorrow night or this weekend. I'll identify the video board using the technical manual, and report back on which one it has.

Thanks!

- Earl
 
Good news - all fixed!

This Kaypro 2X appears to have the Toshiba video board. The "sub-brightness" adjustment is very easy to reach with the lid off. Turned it down just a bit, and *all* the problems went away.

Next stop - replace battery, replace (or just remove) Rifa caps...

Thanks for the help!

- Earl
 
Attached, please see pictures of the video issue I'm having with the Kaypro 2X.

In one picture, I've turned the brightness down all the way. You can still see the horizontal slanted lines on the screen.

In another picture, there is text on the screen from the MITE terminal program. On this screen, you can see that on lines with text, there is a horizontal streak of green on the entire line.

In the final picture, with some inverse text, some bending of the screen is also evident. (Note on this picture that the extra brightness in the middle is the camera - it doesn't look like that in person.)

EDIT: One thing I'm going to try - the Kaypro technical manual describes a brightness pot on the CRT board. It's possible that is turned up too high, causing the distortion. I'm going to try (carefully) adjusting that.

Any thoughts appreciated, and thanks again!

- Earl
View attachment 61614View attachment 61615View attachment 61616

I just went through this with one of my K10s. There should be a secondary brightness control on the video board. Try backing that off slightly. Components and settings drift over time with these machines.

UPDATE: Sorry, I should have read all the responses since Larry already suggested this... Glad you have it solved.
 
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