Kaypro - An Iconic (and Nostalgic) CP/M Machine

Kaypro computers have long been nostalgic for me.  My grandparents had a Kaypro and I remember thinking how impressive of a computer it was.  Very rugged and industrial compared with my VIC-20 connected to a color TV.  I was recently offered a Kaypro from a trusted seller whom I've done business with before and I was most happy to be the next owner of a Kaypro 2X from 1984.

The naming of the Kaypro model numbers is a bit odd, but if you are interested, this article explains the timeline quite well.  The 2X is one of the final machines, but they all looked quite similar to the rest of the line.  I think they may have used the same case dimensions through the entire run of models.  From the outside, the distinguishing characteristic of the later systems is the 1/2 height drives instead of full height.  

My repair story started with finding and reading the relevant sections of the technical manual from BitSavers.  The first problem to overcome was that the CRT display was not working.  You could see that the tube was working, but the display was rolling.  By figuring out which of the three CRTs (Toshiba) was inside, I was able to locate the adjustment Pots and get the display solid.

The next challenge was to get the Kaypro booting.  I didn't have any Kaypro media, but as readers will know I've got a SuperCard Pro flux disk imaging system.  I've recently figured out a new workflow for that which has allowed me to create bootable disk images for several different retro systems, including the DEC VT-180 Robin and now this Kaypro.  Here is that workflow at a high level:
    Find Appropriate Bootable Disk Images for the Target System
    Use HxCFloppyEmulatorSoftware from this page to convert Disk Images into Flux Image Files
    Use Flux Imaging Tool to write out Floppy Disks, in my case SuperCard Pro.

Once I had floppy disks I was ready to try booting the machine. Sadly the unique push-button floppy drives in the machine were not working. Neither drive would eject a disk.  In the short term I was able to find a working DS/DD 5 1/4" drive from my parts bin that worked with the Kaypro.  Jumpering this as Drive 0 I was able to see the machine boot into CP/M for the first time.

Next on the agenda for the Kaypro was a through cleaning.  This was a dusty and dirty machine, both inside and out, but like many of the 80s systems, it was quite easy to take apart all the way down to the board level, so I did this both for the computer and the keyboard.  I washed the housings with warm soapy water and set them aside to dry, then cleaned the circuit boards w/ Isopropyl Alcohol, including the power supply, the analog CRT board, and the logic board.  I also removed the keycaps and washed them, and spent some time cleaning up the switch deck of the keyboard.  I did not try remove any of the switches as all the keys appear to be working on this machine!  I wonder if the enclosure design keeps dust out of the keyboard?

Part of the cleanup process was to return to the two floppy drives.  These were unique mechanisms, Epson SD-521 drives.  Like so many times before, the forums have been quite helpful, and I got some good advice about the cleaning.  After cleaning and lubrication, one of the drives is working well (it was previously the B drive, so maybe had fewer hours on it?).  I was able to get the previous A drive ejecting again, but there is a problem with the drive motor which I was not able to easily troubleshoot, so I've set that aside for now.  

As I was troubleshooting, I made an interesting observation about just how small CP/M even when compared to DOS 3.  One of the floppy drives I was troubleshooting was having trouble w/ the head stepper motor but if I manually pushed the head back to Track Zero (on the outside of the disk), then when the computer would successfully boot into CP/M and even give the Directory listing (DIR).  Trying to load a program would lock up the computer since the heads were not able to move to the correct position.  So this is another drive that I've set aside for now.

The machine doesn't look perfect since the two drives are not an exact match, but I'd much rather have the second drive functional than have it look nice but not work correctly.  The final results for now are shown below...

I'm quite pleased with how it turned out.  The highlight so far as been playing a text based Pac Man clone called Catchum...

It's surprising how much fun a text based arcade game can be.  The Space Invaders clone, called Aliens also looks like it would be fun, but there's a problem with the keyboard mapping for that game, so it isn't working on the Kaypro 2X.

Do you have any memories of the Kaypro computer, or suggestions about software to run on it?  If so, please let me know in the comments below.

Assembling an Apple IIgs - Late 80s & Early 90s 16 Bit Retro Computer

In the fall of 2021, I heard from a fellow member of the Retro Computer community on the Free Geek Twin Cities Discord server that they were selling an Apple IIgs.  This machine had been on my Wish List for some time as it has some nostalgia for me.  The IIgs was the "new powerful" machine for me when I was in Junior High and High School, and I looked forward to using it when I was at school as an upgrade over the Apple IIe.  Also, GS/OS was the first Graphical User Interface that I personally used.

As I've become more familiar with the history of Apple II, I've learned that the IIgs was the most powerful Apple II machine and the “end of the line” for this iconic series of machines.  I was able to make a deal with the previous owner and I got the machine home and started to go over it.  The machine had been at a school and mostly just needed cleaning up.

When I first got the IIgs home I had only the base unit. not the correct monitor or keyboard, but since the machine had a Composite output I was able to connect an older Apple IIe Color Monitor that I already had.  This was the first Apple computer to use the ADB bus, and although I didn't have the unique keyboard, I was able to use a different ADB keyboard and mouse that I already had from a late 80s Macintosh.  With these plugged in along with floppy drives and a FloppyEmu that I already had I was able to get the machine booting and running, and to create floppy disks for the machine.

This machine was a Rev 0 machine (not the "Woz" signature edition).  I discovered that many collectors feel that ROM 1 machines had better compatibility than ROM 0, so I looked for a replacement ROM and was able to find this device.  It was a fairly inexpensive addition, easy to install and easily reversible should I decide to go back to ROM 0.

My IIgs included an original Memory Expansion board that was not fully populated with RAM DIPs.  I was able to source the correct RAM DIPs from Jameco and get that card fully populated, bringing the system total to 1.25MB, enough to load GS/OS.   I will point out that the period correct RAM DIPs were not cost effective, dollar for dollar I would have been better off getting a modern RAM upgrade for the IIgs to bring it to closer to it Maximum RAM capacity.

After working with the IIgs a while, I realized that I was really missing the look of the matching monitor and keyboard.  I put out some feelers with the Free Geek community, and was very pleased when a fellow retro computing enthusiast offered to sell me one of their keyboards along with a IIgs Monitor.  I finally had the "matched set"...

Although I know this is a somewhat common Apple II vs. others that I have collected I've really enjoyed this machine due the nostalgia factor that I have with it.  One the most important lessons of this build was being willing to go slow and accumulate the parts as they came.  As usual, the forums have been a great source of information with a community that is more than willing to offer advice and support.

I'm more skeptical than I was about the value of Retrobright since it's likely that computers will just end up yellowing again.  But in this situation the IIgs itself had stickers on it that I've removed and this has left the base un-evenly yellowed.  Also, the Monitor has hardly any yellowing and the Keyboard is the most yellow of all the items so I will be attempting to Retrobright most of this computer during our long days here in Minnesota this summer.

Other than that, this machine is complete.  I've got a flash based storage solution inside this machine, and I've found and loaded a bunch of games on this machine.  I'm especially interested in the 16-bit games from the late eighties and early nineties because I don't have a machine like the Amiga 500 or Atari ST.  Here's a great YouTube playlist that goes through many of these titles.

A New Addition to the Collection - DEC VT-180 Robin

Knowing of my interest in both Digital Equipment Corporation and CP/M Machines a friend recently offered to sell me his DEC VT-180 Computer, also known as the Robin.  I jumped at this chance and I consider myself very fortunate to be the next owner / caretaker of this survivor from 1982.

My system came with some but not all of the software that has been archived.  I was able to write out floppy disks from the images on BitSavers which are listed here. and I have converted these to the more universal IMD format (Dave Dunfield's Image Disk) and uploaded them to Archive.org.  Also, I used the KERMIT80 software which was included on one of the disks to send data over a serial link to create disks for ZORK 1, 2 & 3, as well as send three floppy disks full of Basic games.  I've uploaded disk images (In IMD format) for this "new" contribution to Archive.org if there are others that can use this.

As we all know, gaming is the "Killer App" for Retro Computers, so I've also tried finding a couple of other CP/M Games like Ladder and a text-based PacMan clone.  The only archives of these that I've found, do not appear to contain versions that will run on the DEC, although I do see one YouTube video showing these games, so I do think they are out there.  Please leave a comment below or reach out via email (address in my Profile) if you have disks you'd be willing to swap, send, or image?

The Robin has been a super interesting machine to learn about.  As many of the earlier personal computers, it has single sided double-density floppy drives, and to make up for that it supports up to four drives at a time.  The machine is hosted inside of a VT-100 terminal.  It has two serial ports, one "general purpose" that could be used for a Modem or terminal emulation, and a second to connect to a printer.  The system is not expandable beyond the ports on the back as there are no open card slots.  This machine is built like a tank, and each of the drive enclosures is also solid sheet steel and amazingly strong.

Perhaps in the future I will blog about a hands on comparison and contrast between the DEC Robin and the IBM PC, but for now I'm just going to bask in the warm glow of the VT-180 experience.  Perhaps it's finally time for me to play through Zork, that's something I never did finish back in the day?

The IBM Model 5150 Personal Computer

In 2021 I saw a tip from a friend on the Free Geek Twin Cities Discord, he pointed out what the seller was calling "one of the early IBM PCs".  I followed up with the seller and was able to acquire the PC without even knowing for sure which model number it was.  As it turns out, it was an original IBM 5150 that had been upgraded over the years.  I was able to roll back some of the upgrades, and install a "stealth" upgrade of my own, an XT-IDE interface to allow this machine to boot from a Compact Flash card.  

One of the downgrades I performed on the machine to get it back to the original look was to install full height 5 1/4" drives into it.  The original machines shipped with Single-Sided drives, but I'd found out about a Minnesota Computer History connection.  One of the companies making "mini" 5 1/4" drives was called Magnetic Peripherals.  Magnetic Peripherals drives were manufactured in Oklahoma City but were owned by the Minnesota firm Control Data in the early eighties.  I was able to borrow a drive out of a different computer, purchase a parts drive from eBay, and I got two additional magnetic peripherals drives off the free pile @ VCF Midwest in the Fall of 2021.  Between these four drives I was able to combine parts and get two working drives.

Here's a picture of the 5150 after I'd done some work on it to restore it...

I have very few memories of this computer from back in the day.  We didn't have this type of computer at school (We had Apple IIs at school), but one of my parents friends did and he let us play games on it when we visited.  I remember being frustrated when I accidentally exited the game we were playing and was confronted with my first DOS prompt.  I didn't know what to do and was surprised when turning the computer off and back on again only brought up another DOS prompt.

In the modern day, we know that the IBM PC was a huge success, and so much has already been written about that, but what can I add about the machine based on my own experiences in 2021 and 2022?

I can report from personal experience that the keyboard, the Model F, is truly amazing.  I still enjoy the buckling spring keyboard and use a Unicomp keyboard as my daily driver, but it's not the same, the vintage board is just so much heavier and has a much better feel and sound.  This is probably the high point of the machine. 

The documentation is also a high point.  This owner had kept all the floppy disks and manuals along with the machine.  The manuals are truly amazing, covering in detail how the machine works.  I understand that this was an intentional decision on IBM's part to copy the openness and expandability of the Apple II that had enabled so many third parties to create compatible hardware for the machine.  So interesting that this design decision, which was intentional and did work as planned also planted the seeds for IBM to loose control of the PC compatible market within less than 10 years.

The 4 color CGA graphics leave much to be desired, although I do find it interesting that out of all the Retro machines and games that I have, both PCs and Apple, my kids ask to go back to Alley Cat over and over again.  The game designers certainly did their best to make this an engaging experience with the 4 colors and PC speaker.

One other item of note I should cover is the overall build quality.  Very heavy sheet metal was used in everything from the base of the keyboard to the top cover of the case.   The build quality surpasses anything that we see in the modern computing era, and I expect these machines will outlive many modern devices.

In summary, I'm very glad to own one of these, certainly an important part of the history of computing and of the Personal Computer revolution.

Making Memories - Core64 Project

As readers of the bLob will know I'm interested in moving "back in time", learning about the history of computing before the Personal Computer revolution.  I've recently been reading the book "A New History of Modern Computing", it's a textbook but quite enjoyable.  It's written in an interesting way, instead of trying to follow all the development streams in chronological order they approach the development of computing from the different groups of users, scientists, data processing, personal use, etc.  I'm only about 1/3 of the way through, but I highly recommend this book.

One of the interesting things I was reading about was the development of memory technologies, specifically of core memory in the mid to late 1950's.  I first learned about core memory at my first job out of college.  Some of the older engineers had worked with the technology earlier in their careers.  I wish I'd recorded what they told me then, but if I recall correctly they had told me that there was a preference to continue to use core memory in military aircraft long after industry had abandoned it because it was nonvolatile.  If an aircraft crashed the core memory could be recovered, the state of memory could be recovered from the time that the computer stopped.  This was the original meaning of "core dump".  This data could be used in crash investigations.

But other that these conversations, I have never seen core memory in use or even had a solid grasp of the principles of operation.   When I learned of Andy Geppert's Core64 kit, I was intrigued.  This kit is great idea, as it gives the builder hands on experience of making a core memory.  In my experience nothing helps me understand an unfamiliar technology better than getting hands on with it.  Building 64 bits of core inspires tremendous respect for the men and women who made core memory.  For example, the PDP8-i had 4048 12 bit words of core (so 48,576 bits of core had to be woven, 759 times more than the Core64 kit!).

I got a great deal of enjoyment from the process of building the Core64 kit.  The documentation is excellent and by tackling a small amount of the weaving process over a few days I was able to complete the assembly that works well and looks really cool because of the interactive nature of Andy's design.

I'd recommend the kit to anyone looking to get a more intuitive grasp of how this technology works.  Here's my unit assembled and operating...

See the kit webpage here for instructions and ordering information if you'd like your own...
https://www.core64.io/

Do you have any connection with core memory technologies?  Let me know via email or in the comments if you ever used a Digital Equipment PDP-8i, or another computer with core.

Walkabout Computing - Hammerhead XRT Tablet

Over the last months I've been buying Retro tech from a gentleman in St. Paul that I met through a mutual friend.  He's been collecting for a long time and has some really interesting stuff.  I think the oldest machine I've gotten from him is an Apple IIe from 1983 but this article is about one of the newest things I've gotten, a rugged tablet computer from 2005 (a Hammerhead XRT from Walkabout Computing).

I'd never heard of this machine before he texted me an image of it and asked if I'd be interested.  I was able to find the Users Manual online, and I was intrigued.  The device is ultra-rugged for Military and other high availability applications, based on the asset tag it looks like this one was used in the airline industry.  When I got a look in person the screen was in good shape.  He didn't have the Power Adapter so I had to buy it without knowing if it would work or not but I've had good success with most of the items I've purchased from this seller so I took the risk.

On getting the unit home I used the Multimeter to probe the power pin and prove to myself that it was Center Positive, I sorted through my power supplies to try to find a 15 Volt unit, or at least a barrel jack of the right diameter.  I didn't find a 15 Volt supply with enough current but I did find the right barrel jack which allowed me to power the unit from a bench Power Supply.

The machine booted!  I was quite relieved, but it turns out that this early win soon gave way to frustration.  Taking the tablet apart I learned that the hard drive had been removed.  It uses a 2.5" 44 pin IDE Hard Drive and I have plenty of replacements so that was not problem, but I also could not figure out the hotkey to enter the BIOS.  Since this is a rugged computer, it's possible that they have this feature locked out, or it could be as simple as me not using a compatible USB Keyboard.  I was not able to find any additional technical detail online other than the Users Manual, some reviews, and a forum thread about running Linux on the tablet.

So, I was stuck with making due with whatever hardware the BIOS would recognize in its current configuration.  The machine does have a single USB port, and I was able to get the machine to boot off a USB Floppy Disk drive, and once or twice off a USB CD drive, but this was inconsistent.  I ordered a second USB 2.0 hub, thinking that I might have a compatibility issue between the BIOS and my USB hub where the machine can not discover CD drives behind the hub, but I have not tested that yet.

In the meantime, I tried to load the OS onto a Hard Drive using another machine, then move it back into the Tablet PC.  For Windows XP Tablet Edition, this did not work.  Perhaps due to differences in the HAL between the two machines, XP Locks Up on boot.  Based on another article I thought I would try an old version of Ubuntu, but long enough after this machine that it might include hardware support for the touchscreen.  I loaded Ubuntu version 10.04 (2010) on the machine, and it booted and runs great!  Such a relief to have something running on the machine, the touchscreen is working as is a USB Ethernet dongle and other USB peripherals as well...

The Specs of this machine are:

Pentium III Mobile @ 800 MHz
512 MB RAM
60 GB HDD
USB
2x PCMCIA Card Slots

Once I got the machine running, a "loose end" was to solder up a more permanent power solution.  As is probably no surprise, the batteries are completely dead on this machine and so it will remain plugged in all the time.  Through testing I determined that the machine would run fine at 12 Volts, and so I was able to find a 12 Volt 3 Amp Power Supply in storage to solder up with the barrel jack for this machine.

So, the remaining items on this machine are:  Continued experimentation to enter the BIOS of the machine and looking for additional technical information online.  Try to load Windows XP Tablet Edition on another PIII machine and see if I can get that booting, and also to find a larger Flash Based storage solution that is recognized by this BIOS (A the current time, I had only a 2GB CF Card w/ adapter, which really isn't enough storage to do anything interesting with this machine, like load the entire contents of Wikipedia in case of a Zombie apocalypse).

Let me know if you've ever used one of these machines, or if you have any background information about the Hammerhead.

Really Old Computers - Simulation Using Kits as a Path Forward

As readers of my bLog will know one of my goals in the Retro Computing hobby has been to "move back in time", learning about earlier and earlier computer systems.  Over the last couple of years as I've built my collection and interest in the hobby has increased prices have risen.  The machines that I can afford to buy (as a hobby) are of a certain age and no older.  The machines from the 70's are becoming out of reach for the average hobbyist, including the 1977 "trinity" of pre-assembled home computers; Commodore PET, Apple II, and Radio Shack TRS-80 Model 1.  For machines that are older than that, the original kit built home computers like the Altair 8800, IMSAI 8080 and more obscure machines like the ones that Brad @ Tech Time Traveller covers on YouTube, prices are also quite high.  

Prior to the Home Computer revolution, computers were purchased by companies in smaller numbers and tended to be quite large, so hardware from IBM and the Seven Dwarves isn't a practical target for an individual to buy and tinker with.  Even early "Mini Computers", systems from Data General or Digital Equipment are beyond the limit for most hobbyists in terms of cost, size, and power requirements.

But, there is an option that I've recently become aware of that I've become convinced is a good way to go for those of us who are just learning and aren't yet certain if we are willing (or able) to make the commitments required.  Emulation has proliferated as one of the many benefits of the Open Source software movement, and Hardware Simulation has become easier since only the User Interface needs to be Simulated with the rest of the functionality easily emulated in Software.  There are some really lovely simulators out there now with front panels like; Adwater & Stir's AltairDuino,  High Nibble's IMSAI replica, and Oscar Vermuelen's PiDP-8 replica.

As Oscar explains on his web page one of the many advantages of pursuing the hobby in this way is that these systems are more stable and reliable than the retro computers themselves.  Learning these systems is complicated when running on actual hardware because the hardware is often breaking down due to component age.  Along withe lower cost and no risk of damaging an actual antique, I find that a quite a compelling list of arguments, so I took the plunge and got in an order for the PiDP8 project.  Based on the instructions on the website I was able to get the Pi setup and running before the hardware arrived, and I had that running as shown in my last bLog article about building what looks like a Retro terminal.

While I was waiting for the kit to arrive a friend of mine reached out about a Terminal that he had acquired as a part of a large lot of vintage gear that he had purchased.  He offered to sell it to me at a great price, an offer I couldn't refuse, so now I am the proud owner of a Digital Equipment Corporation VT-520 from 1996.  This was the last Terminal that DEC made and I believe based on the date code that this may have been one of the last of the DEC branded terminals.  I'm quite happy to have gotten it, and because it is compatible with PC keyboards that also lowers the cost of entry.  I've paired it with a very nice clicky Unicomp from 2001...

Shortly after I got the Terminal online with the Raspberry Pi computer, the PiDP8 kit hardware arrived.  The build was time consuming but very well documented. My son helped me start the build, so that was fun.  It's a great looking build as expected...

I couldn't be more pleased with the build, and I'm going to move other computers around to keep this machine easily accessible so that my learning about the operation of the machine and the software can continue.

Building a "Terminal" out of Retro Parts

As I work my way back in time in my Retro Computing journey, it's time for me to get a Terminal.  Ideally I'd like to get a VT-320 as this is the interface that I remember using most frequently during my college years to access the DEC Vax systems in the computer labs.  These labs were filled with 30-40 terminals each and were large enough for lab classes to meet with everyone logged into the Vax at the same time, or to use for programming assignment when classes were not in session.

As interest in retro computing has risen, so have the prices of these terminals, with these "newer" 20 year old terminals selling on eBay around $300, sometimes without keyboards that could cost another $50 to $100.

What is a retro computing hobbyist to do?  I encountered a suggestion on a kit building website about directly attaching a display and keyboard to a Raspberry Pi and remembered that I still had a few RPi's in storage from projects that I'm not using any more.  What followed is this:

This "Terminal" consists of an early VGA Monitor (640x480 only, not multi-sync), and a nice Omnikey 101 keyboard which I have previously covered on the bLog.  Here's what I did to get the retro monitor and keyboard working with the Pi...

I started with the current base image of Raspberry Pi OS (32-bit, lite version).  I'm running this on an RPi 2, since that's what I had around, but I did want WiFi connectivity so there's a dongle plugged into a USB port.

I plugged the Pi in with a modern USB Keyboard and HDMI Monitor to start, and used raspi-config to setup the networking, enable ssh, change the password, and get the display configured.  Using the information from this article, I set the display resolution to DMT 640x480@60Hz.  After restarting the Pi, I double checked the image resolution and it was indeed lowered to the required resolution.

After checking that, I was able to connect the Keyboard with a PS/2 to USB adapter that I had laying around.  I don't have a model number but if you use a Northgate Keyboard I'd recommend reaching out to Bob @ Northgate Keyboard Repair as I've heard that these keyboards can be somewhat picky about which adapters work well.  Once the keyboard was tested and working with the Pi I moved on to the Retro Monitor.

In order to plug the VGA monitor into the Pi, we need an HDMI to VGA adapter, these are commonly used to connect laptops with old projectors so they are still available.  I used an Inland brand I had around, but I've also ordered a couple of replacements on Amazon here that I will test when they arrive.  Plugging this in, it worked right away.  It's so fun to see the colorful Raspberry Pi Boot menu on this late 80s / early 90s combination of hardware!

Here's a list of the hardware in the build:

    5 Volt Power Adapter (not shown)

    Raspberry Pi 2 w/ Case

    WiFi Dongle for RPi

    Inland HDMI to VGA Adapter Dongle

    PS/2 to USB Keyboard Adapter Dongle

    VGA Monitor w/ Cords

    PS/2 Keyboard w/ Cord

And a picture of what the connections look like at the back.

Longer term, I might add a Serial Port for attaching to other Retro Computers, but my immediate use case is for a kit that I've ordered with emulation running directly on the RPi, so this Pi will be removed from its case and transplanted into that kit when it arrives.  I'm sure I'll be blogging about that when the time comes, so stay tuned!

Do you have an old terminal system, or good memories of using these systems back in the day?  Let me know in a comment, or feel free to drop me an email.

NeXT Megapixel Display N4000A Repairs

 As you may have seen previously on my blog, I'm fortunate to be the custodian of a NeXTStation setup that I purchased at last year's Vintage Computer Festival - Midwest.

Since blogging about that machine, I've recapped the mainboard, added an External SCSI CD-ROM so I can load software the old fashioned way, and upgraded the Hard Drive to a 2GB Quantum Fireball (Fingers crossed, it's still working!).  One outstanding issue with the machine has been that the audio on the monitor has not worked since I owned the machine.

According to this article, on the nextcomputers.org forum, it was likely that a circuit board in the monitor need to be recapped.  I finally got the time to tear into the monitor and have a look.  What I found surprised me, and so I thought I'd put this out here for the community so you can potentially avoid these pitfalls.

First let me start with the obligatory warning about working inside of CRTs.  I recommend you not do what I've done. If you do decide to go ahead, then watch a video or three about how to properly discharge a CRT before you work on it.  OK now that that's over with...

First, it was pretty easy to tear down the monitor, but I did make a mistake along the way removing the stand from the bottom of the monitor.   You don't need to do that, and if you do release the tension on the monitor stand's hinge, it's difficult to get that back in adjustment, so I'd recommend that you not remove the stand or mess with the hinge.

The back comes off with four Allen screws...

This exposes the old school RF shielding.  I'd recommend putting this back on when you are done (I'm looking at you Adrian Black).  The shielding is held on by four screws on one side and five screws on the other, they are all the same length.   When they are off, the housing comes back just a bit to release from some tabs, then can go straight up off the monitor...

This exposes the entire CRT and both boards.  Now would be the time to discharge the CRT if you were following along, which of course you are not because this is dangerous...

The main circuit board cover the back of the monitor, but the sound board is on the bottom of the enclosure.  It cannot be removed without taking the electronics off the chassis, but this is pretty easy to do.  

On the bottom of the monitor, there are two large screws that hold the electronics portion of the chassis onto the sub-frame that holds the tube and the stand.  Removed these two screws...

Disconnect all the cables from the tube, including the high voltage, the yoke, and the tube socket at the end of the tube.  Once they are disconnected, the rear of the chassis with the electronics on it can be pulled straight back.  It may be easier to pull it back just an inch to get your hand in to remove the socket from the end of the CRT.  Once all the wires are de-routed the electronics are more accessible...

The large circuit board must come off the back first before the connector board with the sound circuit can be removed.  There are two connectors going from the large board on the back to the small board on the bottom, remove those.  There are five screws holding it in.  Remove the screws and set the large board aside.  Note:  I did a careful inspection and some cleaning on this board, but I did not see any of the small electrolytic capacitors on this board, so I didn't do any recapping on this board at this time.

The small circuit board is held in by two screws inside, and two nuts on the outside of the enclosure where the cable attaches, remove those...

The circuit board has a Dozen (12) Electrolytic Capacitors. They are 47uF, 16 V rated caps...

Remove and replace the caps.  In this case the monitor was from 1991 and so it was suffering from capacitor leakage and needed some minor rework on a couple of the traces.  I'm glad I caught this in time.

But, there was one more twist in the story.  When I tested the monitor, the audio was not restored to function.  After measuring resistance on the speaker, it was open circuit.  I was able to source a replacement speaker from Rob at Black Hole, Inc, and the monitor and speaker are now functioning normally.

The final hardware upgrade I'm planning for this machine is to replace the Spinning HDD with a Solid State device, but in the meantime I've got alot of learning to do about how this machine works and what its capabilities are.