Kaypro Restore Pt 1: Replaced Sockets and Video Activity Capture

The Kaypro restoration is coming along, but not a lot of headway has been made.  I’ve manage to convert the board back the way it was when it left the factor, as can be seen in the picture below.  However, there is at least one problem with this.  U87 was factory suggested modification, and I have learned both from a reader on this blog as well as a guy on Facebook that it was a service repair of some sorts.  Something about corrupted data.  So that repair will be redone.  I guess it is for the best, seeing as how the previous sockets were worn from the constant pressure of the machine pins over the course of the last 30 years.  Rather that just sacrifice the chip, the person who did the original repairs sacrificed both a chip and a socket.  And the sockets caused the factory placed sockets extra wear. In other words, it needed to be replaced.

The next step was to take a look at the CPU’s activity, and see how everything was going.  And It appears that the CPU is hopping along quite normally.  However, I did notice that the clock appears to not quite be 2.5mhz.  Rather, it appears to be a stable 2.4mhz.  The picture below shows (from top to bottom) the clock signal, the MREQ signal, and the IORQ signal.

All and all, it appears that the machine is running, executing code, and generally performing routine memory operations as well as I/O operations.

As for the video problem.  Well, the good news is that there is at least some type of video signal.  But I’m not sure if it is garbage or actually has something to it.  The pictures below shows (from top to bottom) the Vertical Sync, the Video signal, and the Horizontal Sync.

I’d love to know if anyone knows if this looks pretty standard.  Or if there appears to be something amiss with these video signals.  Because, like I have mentioned in the past, I have no knowledge of video signals or CRT displays.

However, I have see mention before of a pretty easy circuit to fabricate that combines the vertical, horizontal and video signals into a single composite video signal (this was for the Commodore PET). And I may end up sitting down at the bench one day in the next week or so and solder this up.  However, I find it hard to justify using the time for that.  Since I do have my G-80S prototype video board under construction at the moment (another project involving video signals which I have no understanding of).  However, I’ve attached the following picture of a schematic I have found for the mod.  It seems interesting enough.

I have no idea if it’ll work.  But I cannot imagine that the signals are that different.  But who knows, like I said, I know nothing about CRTs or video signals.

So, a little work has progressed, and will hopefully continue.  Also, I’m still looking for a boot disk for the working Kaypro 2X.  If anyone has the ability to make me one for a decent price I’d be a paying customer.  Shoot me a email, and we can talk.

6502 Badge Nearing Completion


My copy of Lee’s 6502 Badge is nearing completion. Lacking only a 2mhz resonator and a slide switch that would fit the board, I have been forced to wait on parts from Mouser. 

I have, however, made some substitutions. Probably the most visible is the choice of EPROM. I have a 27C512 socketed. This is because one can use that as a replacement for the 27C256 provided he places the code in the top half of memory. Second item of note would be the connector that has been added to make a detachable battery pack. I thought it would be a nice addition. Third, I didn’t have the proper resistor arrays, so I used one that was close, and the other I substituted with upright resistors. There is nothing more retro than that… And the last substitute was to make odd sized capacitors work, and replacing the 560nF cap with a 100nF cap. I doubt there will be an issue here. Per my previous conversations with Lee I am under the impression that many times he chooses a part because it’s what he has ‘on hand’, and it works. The alternative was to go with a 560nF Tantalum. It would work, but I didn’t want anything that volitile on my chest (I have seen many Tantalum capacitors go ‘boom’ in my history with older computers).

But, a long story short I only lack those two components and burning the ROM in order to have a working example of Lee’s 6502 computer. 

But I have another problem. I’ve looked high and low, but have not found my TTL Serial to USB adapter. But, what I do have sitting on my work bench are a bunch of CH340G RS232 to USB ICs as well as plenty of 12mhz oscillators. Ok, so that’s something. I also have some MAX3232CPE RS232 to TTL ICs.  So I have options, and should be able to wire something up. I’ve never tried my hand at making my own USB to TTL adapter. But it could be neat. Especially since I have my own 3D Printer. I could make it look decent.

I’ll post an update as soon as it is finished.

6502 Badge Arrives


Thanks to Lee Hart, Retro Depot now has a couple of the boards for his and Daryl’s 6502 VCF Badge.

Since they just arrived in the mail there hasn’t been time to complete them. But that should be expected sooner rather than later. I believe the parts box even has a spare LED display left over from the z80 Membership Card that was built about two years ago.

In either case, as soon as it is completed you can expect a review. And the next time Retro Depot makes it to a Festival, I’ll have a nifty 6502 Name Badge / Conputer with me.

Maybe I should build a portable Terminal so that I can program on the go. Now that’s an idea….

UPDATE: Roadrunner Author Lead

Great news. Evan from the VCF has emailed me concerning the possible identity of the individual responsible for the Roadrunner Monitor. His email was very brief, but I plan on following up with it.

I have contact information including an address and phone number. However, considering this would be a cold contact, I’ve elected to write the gentleman a letter to confirm his identity, and attempt to engage in conversation about the history of the code.

For the time being, all further details are on hold. However, once more information is obtained, I’ll be making another update. Until then, we will all have to wait in anticipation.

FYI, I think I’m just as excited about this as anyone!

Kaypro II ROM Dump – Surprise

This story just keeps developing.  I decided to restore the computer to it’s original state, since the modification appeared to be unfinished, and redundant.  I carefully pulled the ROM, very carefully bent the pin back into the place, and placed the rom into my programmer to preserve the code that was within.

Upon reading the code to memory, I was stunned.  I half way expected to see something along the lines of two separate versions of code.  However, what I saw was something entirely different.  What I saw was this:

This ROM was an aftermarket ROM developed by a gentleman by the name of Howard Saltzman, of Baltimore Maryland.  And was sold by Highland Microkit.  How cool!  But what was it?  I hadn’t the faintest idea.  So, I went to google…and came up empty handed.  Searching for “Howard Saltzman” and “Baltimore” didn’t return much.  And I spent a few hours trying different combinations.  That is until I searched for “Highland Microkit” and “Saltzman”.

I then came up with something odd.  A hit for a PDF file from a magazine called “Profiles.”  It was apparently a magazine geared towards the Kaypro in one way or another, but not excluding other computers entirely.  The particular magazine I found was this one here.  Or, if the link dies, you can download from Retro Depot here.  On Page 77 there is an add for a company called Highland Microkit, which advertises a rom called the “Roadrunner Custom Monitor”.  Well, sure enough if I scroll down to 0x01B0 it clearly identifies itself as the Roadrunner ROM v1.5.  But what does it do?  And why have I not seen this ROM listed on any websites which store backups of Kaypro images?

In either case, you can download the ROM Image right here.  It is saved as a text file, but it is actually a binary.  So you’ll need to rename it to “.bin”.  It’s the only way my server would allow it to upload, since it poses a “security risk” being a binary.

I’ve tried to track down Mr. Saltzman, and the closest I’ve come so far is that he attended an engineering college in Maryland, may have become a professor, and ultimately retired some time ago.  He is likely 61 years old from what I can gather on LinkedIn.  But I cannot find any contact information on him.  But if ANYONE knows who this man is, I’d LOVE to talk with him about this ROM.  Who knows, maybe I have the only surviving example out there.  And if that is the case, he very well may want a copy.

Details will be given as they are learned, but it would appear that we are learning quite a bit about this old work horse.  But lets see if we can track down Mr. Saltzman.

Operation Speed Racer Was A Success

Thats right boys and girls.  Operation Speed Racer was about acquiring two, yes two, Kaypro “luggable” Computers.   I found out about the computers on Tuesday the 19th of September.  They were located over in Springdale Arkansas.  That being a drive of about two hours from Tulsa, I figured that it was worth the shot of seeing if they were still available.  To my surprise, since they had been listed for about two weeks, the were still available.  And best news yet, the prices was $57.  And that included not one, but two computers, and the documentation that came with the original software package (MS Basic, S-Basic, CP/M, Perfect Writer, etc.), but no disks.  :o(

I made arraignments with the owner to drive over and meet the owner on Saturday.  And hoped that someone didn’t pick up the computers from him/her while I was forced to wait due to work.  Friday came, and I emailed the owner to confirm that he/she would be available on Saturday, and very quickly I had a reply with a phone number and address.  Everything was looking good.

I loaded up my son after having worked part of the morning, and we hit the road headed to Springdale.  Once at the address, I called the number to confirm I was at the right location.  An older lady answered the phone, and told me she was coming outside.  She promptly came out and and guided me over to where she had placed the computer.  Showed me what she had, and told me the story of where these machines came from.

The story is that she was friends with the Widow of a Professor from the local university.  And that these computers were his babies.  She didn’t know exactly what he had taught.  But that he was supposed to be the original owner of at least one of the computers.  But she she wasn’t sure about the second.  She let me know that he had died about 15 years ago, and that the widow had eventually given these computers to her.  And after quite some time she figured they were just collecting dust, and decided to be rid of them.  After looking closer at the computers when I returned home there seems to be a name scratched into the keyboard G.L. Wheeler.  I’d love to hear about the guy if anyone knew him.

I explained that I collected older computers, and she seemed happy that they were finding a good home.  We exchanged money for computers, wished each other a wonderful weekend, and the boy and myself were back on the road headed home.

Several hours later we were unloading the car and bringing the computers into our home.  I made room on the kitchen table (i.e. My workspace), and began examining the computers.  I had noticed upon picking them up that one had a switch that had been placed internally.  I assumed it was for bank switching the ROM (it’s a pretty common thing to see this on older computers).  But I wasn’t entirely sure.

After an initial inspection i took note that both computers looked to be in ok shape.  However, the computer that had the toggle switch coming out the back vent hole appeared to be modified (I’m assuming to allow bank switching).  See below.

These ICs have been removed from the socket, placed into another socket, modified with bodge wires, and then reseated into the original sockets with a toggle switch running to the back of the machine, and a single wire running to the floppy header.  Interesting, but I have no idea what the owner was doing here.  It would seem that it would definitely have something to do with banking memory though.  Seeing as one of the ICs was connected to a 2732’s  A11 pin.  What I’m not entirely sure of yet is whether this is a character ROM, as the bios seems to be another chip towards the back of the board.

After inspecting the computers I tried powering them on. Now, the first computer, a Kaypro 2X, boots just fine from what I can tell.  However, I have no boot disk to confirm that it does in fact work.  And no way to currently make a boot disk. So I’m going to be stuck for a little while.

The second computer, a Kaypro II, did not boot.  And had a high frequency low volume chirp coming from the power supply area.  I probed around on the power rails for a few moments and noticed that there were no DC voltages.  So, it’s time to start unplugging things.  The first two things which seemed to be the easiest were the Floppy Drives.  After unplugging them, the chirping was gone, and the rail voltages read +4.8v, +11.8v, and -12.0v.  Ok, so now I have power.

However, there was still a problem.  First, obviously one of the drives has a problem (likely a shorted capacitor, not a big deal).  But more importantly, the CRT wasn’t showing any signs of life.

Rats.  I know nothing about CRTs.  The only thing I do know is that it did not appear to turn on.  However, looking at the back of the neck of the CRT while it was turned on it is clear it is getting voltage.  As there was a red glow coming from the back of the neck.  But, I’m deathly afraid of high voltage, so I’m not sure I want to mess with it.  It may be a job for an old TV repair man.  I’m not entirely sure there is even a video signal coming from the board.  I’ll have to break out my oscilloscope and see.  But that will have to wait until there is more time to tinker with it.

But until then, if anyone has any idea what could be going on, I’d love to hear from you.  Also, if anyone has, or can write, a boot disk for a Kaypro 2X I’d love to discuss it with you.

Operation Speed Racer

I have recently stumbled onto an opportunity to acquire another z80 computer.  This is not a homemade computer, but rather a commercial variant.  I’m not releasing the details just yet.  However, I have decided it is worth it to update the community as to the nature of the operation.

I’m calling it Operation Speed Racer because I’m going to be running short on time, and need to meet the individual to grab this computer before he/she decides to let it go to someone else.  From what I can gather he/she has been sitting on it for a while, and is ready to be rid of it.  But the price that they’re letting it go for is ridiculously low.  The big part of the transaction is the drive.  I have to drive several hours away to pick up the computer.  But luckily, the current owner has acknowledged that I’m willing to drive several hours away to acquire what he has.  Let just hope that doesn’t work against me when I get there (read: price jump).

Either way, the operation is a go and I will be spending about 5 hours of the day driving over to meet with the current owner and coming back before I’ll have any additional information to post.  Of course, this all comes after I spend over half the day working at my day job (Clients always have issues).  And that doesn’t include the time I must spend once I get back examining the equipment and determining the condition.  So all things considered, I will likely not have any detailed information until later into the weekend or early next week.

However, I will make sure that I reveal the identity of the computer once the mission is successful.  But until then, I’m not counting my chickens before they hatch. You’ll have to wait to confirm that I do in fact have them in my possession.  But here is to a great Vintage Computing weekend.

Stay Posted.

Grant Searle’s z80 Computer

If you’ve searched any portion of the internet for the terms “homemade” and “z80”, there is a high probability that you’ve run across Grant’s Page.  Grant’s work is essentially the Holy Grail for the beginner.  He gives you the tools you need to have in order to understand how to build a generic z80 circuit.  As well as well documented software which can be modified fairly easily.

Grants circuit gives you a very basic (pun intended) serial based computer running Microsoft Basic 4.7b (a variant actually written by another individual who’s name escapes my memory at the moment).  The computer’s I/O is interrupt driven by the 6850 UART, and has enough leftover space in the ROM to place a monitor or any other code that you’d like to use.  The computer’s original speed is 7.3728mhz.  However, the example above has been modified to use a 1.8432mhz oscillator.

Even regulated down to a quarter of the speed of the original, this computer is more than capable of handling most basic programs.  And with 32kb of RAM, you’ll likely not find yourself running out of program space.  And programs can easily be transfer from a PC to the computer by simply typing the programs into a text file and then copying and pasting them into your terminal program.

Added breakout pins around the z80 on my personal computer allow me to prototype circuits and test them with the IN/OUT commands in basic.  A handy feature indeed.

If you’re looking for a simple circuit to build, and you’d like to have your own homemade z80 computer. Might I suggest that you head over to Grant’s website, and give one of his examples a try.

TEASER:  There will likely be another z80 Computer article coming in the following days.  Not to give too much away, but it DOES NOT involve a homemade example.  I’m working out a deal to acquire something special.  I’ll know the full scoop within the next 24 hours.  Until more is known, we will be referring to this as “Operation Speed Racer.”  I’ll let your mind go crazy now…

Francois Rautenbach’s work on Rope Memory

The early computer and navigation systems used by NASA are extremely interesting, even in the modern day.  The ways that they computed, stored data, and were interacted with are quite different than what we typically think of when we reference a computer in today’s modern age.

However, Francois Rautenbach has been made aware of the discovery of  Rope Memory. And has worked quite hard on a method for dumping the programmed contents thereof.  The video is below.   And a followup video he posted sheds a little more light on the subject.  But my question I have to ask is, is the data still valid?  From what I can gather from my examination of the video, the module is made up of magnetic core storage, similar to early RAM.  And as such, likely lost it’s data a very long time ago.

Open Source CoCo Cartridge Shell

It’s no secret that I love 3D Printing.  It allows the everyday individual the ability to prototype and produce enclosures that are professional.  Or the ability to print that figurine that you found on Thingiverse.  But whatever your 3D Printing Desire is, you know it’s the wave of the future for the Maker.  And you likely want in.

I only recently bought my first 3D Printer.  In March of this year I became the proud owner of a Da Vinci Pro 1.0 printer.  And it while it does take experimentation to master, it is very rewarding.

Several years ago I became the proud owner of a Tandy CoCo 2 64K computer.  I didn’t have any cartridges for it.  But I did have a tape recorder and a great understanding of BASIC.  I wrote several programs, but that was mostly just to tinker.  And to show my son exactly how things were done back in my youth.  And while I occasionally looked at buying some cartridges for the CoCo, I never did.

Now another well known fact is that I love playing with electronics.  I have just about every tool that I could need as a hobbyist.  Up to, and including, a 54 Channel Logic Analyzer.  Being this well equipped, I eventually decided that I just needed to sit down and design a PCB for the cartridge.  And I set out looking for schematics for the boards themselves.

It was at this time that I came upon THIS WEBSITE.  Someone had already created a pretty decent PCB, and uploaded the files for the world to use.  So I thought to myself,”Hey, why don’t I just use this guy’s stuff!”  And so I downloaded the Gerbers, and ensured that all was OK.  I then uploaded the files to my favorite board house, Elecrow.  And once paid for the wait was on.

Now if you never have done business with Elecrow, I’ll fill you in.  Once you pay for the boards they get right to work.  Usually having your board in production within two days.  Once in production it usually takes about three to four days, and they send you an email letting you know that your boards are shipped.  With this email they’re nice enough to send a picture with your  vacuum packed boards and the invoice for your order.

About three weeks later I discovered a package in my mailbox.  Once opened I discovered that not only did I receive the 10 PCBs that I ordered for about $15.  But I also received 5 more “bonus” boards.  I guess they had leftover space on the ENIG Finish panel, and just decided to be nice.  I’m not complaining.

Upon inspection, I honestly could not be happier.  While there are a few small issues, such as the solder mask not quite sticking to the small traces of the ENIG finish (see below), the boards looked great.  I promptly soldered up a “test” board so that I could test individual EPROMs in my CoCo.  I feel this is important to do before committing to soldering an EPROM into a board.  You never know if it’s going to work as programmed.

The boards, and the EPROMs, turned out to work great.  But this left me with another problem.  I didn’t have any cartridge shells.  And moreover, I didn’t have any way of knowing the dimensions of the normal CoCo shell.  Nor if these boards would fit in the every day CoCo shell.  Well, I guess I’ll just have to design my own.

After a few days in AutoDESK 123D Design (Why did they ever discontinue this awesome software!?!?!), and a few test prints of course, I had a basic design.  Ready to test.  And the best part about it, it was practically free….because, I made it!

While I wouldn’t say that this design is authentic to the styling of the original cartridges, I will say that it is very close to what you would expect of a cartridge shell from that era.

And the best part, I’m providing the STLs for free over on Thingiverse.  You can find them HERE.

And you can watch my YouTube video below.