Reviving a Kaypro 4

[Mikseri123]

Hello!

I recently came into posession of an old Kaypro 4 machine that does not seem to function correctly.

Little bit of background on the computer, as far as i know it was put away in working condition and was in dry, clean, room temp storage for who knows how many years before i rescued it.

Whenever i turn on the machine it does start, the power and drive A lights come on and the drive starts spinning (but it does sound very rough), after a few seconds the screen starts to glow but no text is displayed, altough i noticed if i turn off the machine and then quickly turn it on before the screen fades to black, some random characters pop up on the bottom 1/3rd of the screen and seem to kind of "fall down" off of the screen, when typing it sounds like it is doing something but it doesn't seem to properly react when i for example try to type "B:" to try switch to drive B. The video board seems to be the Toshiba variant based on the manuals i have found.

I am very new to vintage computers but i have some experience in vintage audio electronics so i know the basics, but i looked around the internet and this forum for threads with machines that have similiar problems to mine and i have done some checks like checking the +5v and +12v rails and CPU clock and they seem to be fine. I am aware i need to replace the rifa caps in the psu and i am working on getting the parts but they seem to not have compatible ones at my local electronics store so that might take a while and i would like to order all that i need at once. I did measure the filter caps and they seem to be more or less in spec with regards to capacitance but i can see some cracks on them.

I do have access to a basic digital oscilloscope, soldering equipment and a multimeter aswell as a bootdisk but i am honestly pretty nervous about working around the video board because of the high voltages so i don't want to go around poking at stuff all willy-nilly.

With the drive sounding as rough as it does i think i will propably need to do some mecanical maintenance on it but i was wondering if anyone had any ideas on where to continue with the other troubleshooting?

 

[ldkraemer]

First thing to do is open the top of the Kaypro and get the Motherboard Number and the Number's
on the EPROMS. This will lead you to the proper Schematics. While you are in there check that the
EPROMS are well seated plus any other IC's that are in IC Sockets.

Then Download the Version F Tech Manual.
https://u.pcloud.link/publink/show?code=kZco2f0Z1WMvRbWgUTXypEUP2YfC90nWBPb7

Now have a look at the Floppy Drives. If they are full height TANDON TM-100's you need to check
two things. The Drives will have to be removed for the 2nd check.

1. Open the floppy Doors. Shine a flashlight into the hinge area and look for two short White Nylon Pins.
If you see two White Nylon Pins you need new Hinges. If you see a full length Brass Rod, they Drives
are likely good to use. If you need hinges, they are available. I have lots of SPARES.

2. Remove the RPM board from the Back of the Tandon TM-100. Look for two 16 Volt 47uF Caps.
If the acid has leaked from them, the PCB traces will be eaten away. If the PCB traces are good, then
REPLACE both CAPS. If they need repaired I can use Hollow Copper Rivets to rebuild and test the RPM
board.

3. I would clean the head guide rods with Alcohol on the Tandon's. Then lubricate them with a few drops
of Dri-Slide a motorcycle lubricant that does not attract dirt. Most Motorcycle shops carry Dri-Slide along
with Walmart. A can will last a lifetime.

You can also get the Information on the Video Board that is in the Kaypro. It will be one of four as
shown in the Manual. Some Schematics are available for some Video Boards.

Larry

 

[Istarian]

If you have a nice uniform glow on the screen then your CRT display is probably operating acceptably well, there's just nothing meaningful being written to the video memory

 

[Mikseri123]

First thing to do is open the top of the Kaypro and get the Motherboard Number and the Number's
on the EPROMS. This will lead you to the proper Schematics. While you are in there check that the
EPROMS are well seated plus any other IC's that are in IC Sockets.

Then Download the Version F Tech Manual.
https://u.pcloud.link/publink/show?code=kZco2f0Z1WMvRbWgUTXypEUP2YfC90nWBPb7

Now have a look at the Floppy Drives. If they are full height TANDON TM-100's you need to check
two things. The Drives will have to be removed for the 2nd check.

1. Open the floppy Doors. Shine a flashlight into the hinge area and look for two short White Nylon Pins.
If you see two White Nylon Pins you need new Hinges. If you see a full length Brass Rod, they Drives
are likely good to use. If you need hinges, they are available. I have lots of SPARES.

2. Remove the RPM board from the Back of the Tandon TM-100. Look for two 16 Volt 47uF Caps.
If the acid has leaked from them, the PCB traces will be eaten away. If the PCB traces are good, then
REPLACE both CAPS. If they need repaired I can use Hollow Copper Rivets to rebuild and test the RPM
board.

3. I would clean the head guide rods with Alcohol on the Tandon's. Then lubricate them with a few drops
of Dri-Slide a motorcycle lubricant that does not attract dirt. Most Motorcycle shops carry Dri-Slide along
with Walmart. A can will last a lifetime.

You can also get the Information on the Video Board that is in the Kaypro. It will be one of four as
shown in the Manual. Some Schematics are available for some Video Boards.

Larry

Thanks for the response Larry!

Based on the mainboard and the manuals you linked it is a 4/83 model so that is good to know. The socketed ICs and EEPROMs look to be seated well, I can see that U19 is soldered in a bit off kilter but seems to be fine.

The drives seem to indeed be TM-100's, I can see the nylon pins in the hinges, why do you say the hinges need to be replaced since they feel like they function fine?

I can see the 47 uF caps you mention and they look to be fine but I will need to hunt down my imperial sized tools to get the drives out to check and replace them.

Ok, I will give the rods a clean once I get the drives out and disassembled. I live in Finland so I don't think we have Dri-Slide available here, atleast I have never heared of it before, but I will take a look at it to see what would be a suitable local replacement.

If you have a nice uniform glow on the screen then your CRT display is probably operating acceptably well, there's just nothing meaningful being written to the video memory

Yeah it seems to be a uniform glow, when I first got it I could only see a glow in the bottom left corner but once I disassembled it to take a look at the rifa caps and put it back together the glow is uniform and the "falling" letters I mentioned seem to display nice and crisp so i think you are correct.

So would that indicate that maybe the EEPROMs have been erased over time and need to be rewritten? I think I saw somewhere that it should prompt for a floppy on screen if you don't put one in when booting.

 

[Mikseri123]

Update: I took out the drives, changed out the caps, and cleaned and relubed the rods for the drive heads and when i reassembled the machine and turned it on the drives sounded way better and it did display the "Please place your diskette into Drive A" screen, but when i turned off the power and placed the floppy in there and turned it back on it would just show the even green glow on the monitor even after several minutes of waiting and it does not seem to display the text anymore even if i remove the disc from the drive. So it worked for a second and now does not again.

 

[Istarian]

Thanks for the response Larry!

Based on the mainboard and the manuals you linked it is a 4/83 model so that is good to know. The socketed ICs and EEPROMs look to be seated well, I can see that U19 is soldered in a bit off kilter but seems to be fine.

The drives seem to indeed be TM-100's, I can see the nylon pins in the hinges, why do you say the hinges need to be replaced since they feel like they function fine?

I can see the 47 uF caps you mention and they look to be fine but I will need to hunt down my imperial sized tools to get the drives out to check and replace them.

Ok, I will give the rods a clean once I get the drives out and disassembled. I live in Finland so I don't think we have Dri-Slide available here, atleast I have never heared of it before, but I will take a look at it to see what would be a suitable local replacement.

Yeah it seems to be a uniform glow, when I first got it I could only see a glow in the bottom left corner but once I disassembled it to take a look at the rifa caps and put it back together the glow is uniform and the "falling" letters I mentioned seem to display nice and crisp so i think you are correct.

So would that indicate that maybe the EEPROMs have been erased over time and need to be rewritten? I think I saw somewhere that it should prompt for a floppy on screen if you don't put one in when booting.

The only way to know for sure about the ROMs (probably UV eraseable or OTP EPROM unless somebody replaced them) is to use a dedicated reader and see if they contain valid data. Multiple passes might be needed to ensure what you got reflects what is actually on there.

I think bad memory (RAM), flaky logic, or mechanical failure of solder joints or the sockets is more likely than the ROMs having lost their contents.

 

[ldkraemer]

You should have just inserted the floppy and closed the door on the Tandon TM-100.
You DO NOT WANT to be Turning Power ON & OFF with a floppy INSERTED in the
Drive, with the Door Closed. You stand a chance of clobbering the floppy.

If the Drives have the Short White Nylon Pins installed, it's likely that the actual hinge part is broken
and not allowing the floppy to be loaded properly. The Hinge part and full length brass rod
will fix that problem.

If you look closely at the hinge part, you will see the Hinge has a "C" shape that holds the Short White Pin.
It will be broken on one side. The replacement parts are Resin Printed using TOUGH Resin and should never break.


Larry

 

[Mikseri123]

The only way to know for sure about the ROMs (probably UV eraseable or OTP EPROM unless somebody replaced them) is to use a dedicated reader and see if they contain valid data. Multiple passes might be needed to ensure what you got reflects what is actually on there.

I think bad memory (RAM), flaky logic, or mechanical failure of solder joints or the sockets is more likely than the ROMs having lost their contents.

I see. So probably the best course of action would be to inspect the solder joints for cracking etc. and maybe reseating the socketed ICs?
The machine suddenly working for a second after messing with the drives makes me feel like it could be something with them too?

You should have just inserted the floppy and closed the door on the Tandon TM-100.
You DO NOT WANT to be Turning Power ON & OFF with a floppy INSERTED in the
Drive, with the Door Closed. You stand a chance of clobbering the floppy.

If the Drives have the Short White Nylon Pins installed, it's likely that the actual hinge part is broken
and not allowing the floppy to be loaded properly. The Hinge part and full length brass rod
will fix that problem.

If you look closely at the hinge part, you will see the Hinge has a "C" shape that holds the Short White Pin.
It will be broken on one side. The replacement parts are Resin Printed using TOUGH Resin and should never break.


Larry

Oh that makes sense, like i said i am new to vintage computers. My toughts were that it would be safest to insert the floppy when things are not moving. But the good news is that i do not see any damage to the floppy itself.

I took a closer look at the pin holders on the hinges and they look fine to me but I will definetely look into getting some replacements. The machine was used in academia so i think it was handeled a bit more carefully than an average Kaypro.

 

[Mikseri123]

I took a look at the joints for any cracked solder etc but the only real thing of concern i found was some sort of burn/corrosion next to one of the M3764-20RS ICs pins, i cleaned it up and reflowed the joints with a bit of flux but it does not seem to have helped any.

I took a look at the signals that the manual shows in the part where it talks about the mainboards and all looked fine to my eye. Also tried to see the video signal from the J1 connector between main and video boards, sync signals were fine but i have no idea what the video signal is supposed to look like so attached are a couple photos of it if someone can tell me if it looks right or wrong?

 

[Istarian]

Someone who knows these systems well might have more to say here, but neither of those signals looks especially video-like to me.

You might want to double check your test points and consider what the reference voltage ought to be.

http://messui.polygonal-moogle.com/comp/kaypro_tm.pdf

You may find the document linked above helpful. It's written with respect to the KayPro II, but as the KP 4 and KP IV are an evolution of the earlier unit much of it may still be applicable.

 

[Mikseri123]

Someone who knows these systems well might have more to say here, but neither of those signals looks especially video-like to me.

You might want to double check your test points and consider what the reference voltage ought to be.

http://messui.polygonal-moogle.com/comp/kaypro_tm.pdf

You may find the document linked above helpful. It's written with respect to the KayPro II, but as the KP 4 and KP IV are an evolution of the earlier unit much of it may still be applicable.

Yeah i thought as much tbh. The point i tested from is the connection between mainboard and the videoboard and it only has 3 signals, 2 clocks and the output from the multiplexer that sends the parallel dot pattern to the video driver.

Thanks for the document, altough i did allready have it from Larry's link. But you sending it prompted me to take a better look at it and i think i am starting to get a bit of a clue at least, altough i am a bit overwhelmed with all the info since my earlier experience is mostly just audio amp circuits and stuff like that but i think i will have to just hunker down and try to find as much info as i can and try to put it together.

 

[ldkraemer]

If you are sure that the Floppy Door Hinge parts are not broken, you should be able to locate a 3/32"
piece of Brass Rod and cut a piece 38.3mm long to replace the two Short White Nylon Pins.
The Short White Nylon Pins get mis-aligned and that causes the Hinge part to break.

If you know of someone with a Resin Printer, they can print you some SPARE Hinges.


Larry

 

[Mikseri123]

Thanks for the tips Larry! I will try to find that brass rod.

If anyone here has any insight into trying to figure out the booting/display problem i would greatly appreciate any help!

 

[ldkraemer]

You always start with VERIFYING the +5.0VDC Power Supply, the +12 VDC Power Supply,
and the -12 VDC Power Supply. If those check good, then start with the Z80 CPU.

Verify that you have a Clock Signal on Pin 6. And ALL INPUTS to the Z80 are HIGH, as these
Signals are ACTIVE LOW.

Pin 16 - INT
Pin 17 - NMI
Pin 24 - WAIT
Pin 25 - BUSRQ
Pin 26 - RESET

PIN 6 - CLOCK


Larry

 

[ldkraemer]

If the above tests are good (VERIFIED) then REMOVE the ROM and replace it with a clean
EPROM. Then Power UP. The screen should fill with 9'9'9'9'9'9'9'9


Larry