Author: Croccy22

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Dragon 32 repair

The Dragon 32 was an 8-bit computer based around the Motorola MC6809E CPU which meant it was very similar to the Tandy TRS80 CoCo range of computers.

This particular example came to my collection as a nonworking example. When powered on the screen just showed a load of garbage. After dealing with a couple of other computers with this chip layout, I knew that the video chip works independently of the CPU, so the fact it was displaying garbage on the screen, likely meant that the CPU was not running the correct code.

A first check over with an oscilloscope showed that all the data and address bus lines seemed to be active, indicating that the CPU was at least attempting to run something. When a Dragon is first turned on it will perform a CPU reset and then start executing the ROM code from address $8000. I checked the reset line on the CPU which was functioning as expected (Low then High).

Maybe the ROM was faulty? This Dragon has two ROM chips, one lower and one upper, each 8k in size. The lower ROM chip contains the code to clear the screen, so if that chip wasn’t working then we would see the garbled screen. But also the upper ROM chip contains the reset vector for the CPU (It is this that specifies where to start running the ROM code from). So if either of these chips were dead, we would have an issue.

The ROM chips in this machine are 2364 EPROMS. Unfortunately, these can’t be read by the TL866 programmer I have, so I had to build an adapter to make it read as an M27C128 chip. But once I had done that, I verified the contents of the two ROM chips and they both came back fine, so not our issue here.

Computers that use the MC6809 CPU also tend to use another chip named the SAM chip. This chip does the address logic. So if this chip was bad, then when the CPU tried to read the ROMs, it might not actually be succeeding. I went over the pins on the chip and couldn’t see any obvious fault here either. Luckily my TRS80 CoCo2 computer uses the same SAM chip and it was socketed, so just to rule this one out I swapped them over and confirmed that this chip was fine.

If the RAM is faulty, then any instructions that the CPU stores data in memory won’t work. So once again this could cause the computer not to start up. But I checked all the CAS and RAS signals, along with the address pins and the data in and out pins, and I couldn’t see any obvious issues.

I decided then to dig out the datasheet for the CPU and started going over each pin to see if they looked like they were performing their duty. It was at this stage that I noticed the Read/Write pin on the CPU was stuck high and was never changing its value. Without this pin changing, the CPU will always be reading from the data bus but never writing to it. There is no way it can initialise the video chip without writing to the data bus. Unfortunately, the CPU in my TRS80 CoCo2 was soldered into place and I didn’t fancy removing that so I had to wait for a new CPU to arrive off eBay.

Once the new CPU arrived I swapped it out and powered up the Dragon, this time to be treated with the Microsoft Basic boot screen! A fully working Dragon 32 is now in my collection.

I have also discovered that my CoCoSDC adapter also works with this machine so I have an easy way of loading up some Dragon games from SD Card.

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Tandy TRS-80 CoCo 2

After playing around with the Video Genie system which was a clone of the original TRS80, I decided it would be fun to explore the Tandy line of computers a bit more. So after looking around a bit I settled on the TRS-80 CoCo 2 (Color Computer 2).

This particular example had the benefit of coming with the CoCoSDC which allows you to load the entire TRS80 software inventory from an SD Card. It even has a nice menu system to make the loading process nice and simple.

I’ve always wanted to try on the game Dungeons of Daggorath which is part of the storyline for Ready Player One (The book version).

Anyway, here it is:

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Video Genie EG3003

This one is something a bit different. The Video Genie EG3003 is a hong kong made clone of the Tandy TRS-80 computer. It was sold under several different names worldwide such as the TRZ-80 and the Dick Smith System 80. But for us UK folk it was the Video Genie.

Although it was a clone of the TRS-80, it did have a few differences which meant that compatibility wasn’t 100%. The Video Genie also went through a few hardware revisions to make it more compatible. But the version I have was the original version 1 machine, which was known for not loading cassettes very reliably from the internal tape drive, and also missing some fairly vital keys from the keyboard!

This computer had apparently been stored in the upstairs room of a 2nd hand shop until someone asked them if they had any old computers, they dug this thing out and it changed hands a couple of times before it found its way to me.

This has been an enjoyable project for me as the system had a few different faults going on so gave me the chance to do some diagnostics and repairs. I will be doing a full write-up on what went on shortly so be sure to subscribe to my newsletter if you are interested in that.

For now, I will finish with a photo of the machine as I received it. It’s a big computer!

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Apple IIc – The first Apple in my collection

With the exception of an original Apple iPad and an iPod Nano back in the day, I’ve never owned another Apple device. On the mobile side, I’ve always had Android devices from their first release, and from the computing side, I’ve always been in the PC camp.

But back in the time of the 8-bit computers, I don’t think I was even aware of Apple. Living in the UK, I was brought up with names such as Sinclair, Commodore, Acorn and Amstrad. But on the other side of the pond, Apples seemed to account for a vast number of people’s first home computers.

Well, I figured it was about time I found out what all the fuss was about and recently came across an Apple IIc up for sale. It had the Wdrive SD card floppy emulator with it, and I’ve also built up an RGBtoHDMI board for it and purchased a joystick port adapter to allow me to use PC gamepads with the computer.

I am currently running a Hard Drive image on the Wdrive named Total Replay, which has a large selection of the best Apple II games installed with a nice GUI to control it all. It even has a nice “attract” mode which scrolls through some of the games if you leave it sitting there doing nothing.

Going to spend some time now looking around the system and seeing how it all works. Getting used to such oddities as the Delete key not actually being a delete key and instead just printing a weird square character. Apparently, this is a real thing!

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Super Slim PS2 (Hardware Mod)

After seeing a YouTube video about a modder that had made a super slim version of the already slim Playstation 2, I couldn’t resist building one myself!

This mod takes a 79xxx Series PS2 Slim (Which had a smaller main PCB than other models), then trims it down a bit more and removes the optical drive. Instead of loading from CD/DVD, it uses an internally wired MX4SIO adapter to load games from Micro SD Card.

The modder named Wesk, has also designed a really nice 3D printed case design to house the project. Keeping the design in line with the PS2 slim model, this really looks like something Sony themselves could have produced.

As you can see, compared to the original fat PS2, this new console has gone on quite a diet!

If you want to build your very own super slim PS2 then you can check out a good YouTube video here.

The only issue I came across with this project, is the PS2 version I picked up didn’t have the lid detect switch in the same place. So I had to hot glue my own switch into place. Apart from that everything else worked fine and it wasn’t a difficult project to complete.

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Bedroom re-decorated

The bedroom needed a new carpet so I decided to go for a re-design. Originally I was going to build another custom unit, but after measuring IKEAs Kallax units, it turned out that for once, they were exactly the right size for what I required.

So one trip to IKEA later and a lot of work and cables, here is the finished product!

Everything is connected to Alexa-enabled smart plugs so it’s all voice-controlled rather than having to mess with switches. Also, there is a new 10-way automatic scart switch box to switch all the inputs without having to swap any AV leads over.

I’ll see about doing a review of the scart switcher soon, but just as a heads up, it’s brilliant and works flawlessly!

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Nokia N-Gage #sidetalking

The only thing I really remember about these devices when they came out, was everyone taking the **** out of them for having to hold them sideways to use them as a phone.

Well besides that issue, the device itself could actually run some pretty good games for the time. Games like Tomb Raider got their own port for the system, and apart from the weird portrait screen, it was pretty playable.

One other big complaint people had about them was having to take the case off and remove the battery to change the game card. This however is no longer an issue since cracked games are easily available now and you can just fill up a 1GB MMC card with all the games you want and just leave it in the system.

I look forward to seeing what other games the system has to offer, already found a pretty good version of Rayman 3 which I have never come across on any other system as this is a 2D platformer like the original Rayman.

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Nintendo Virtual Boy

The Virtual Boy has always intrigued me, a bit like a VR headset, it’s one of those devices that people cannot show you what it is like in a video or a screenshot. You just have to experience it for yourself.

I had previously heard a lot of people complaining of headaches and eye strain etc, but a lot of people suffer from those sorts of things with modern VR headsets too and I’ve never had any issues with them. So I finally decided to take the plunge and add one of these devices to my collection along with a flash cart so I can experience the entire library.

I must say I am actually quite impressed, I mean it’s not actually VR in any way, it’s more along the lines of a 3D Gameboy, but the effect is really good and the games I have played so far have also been very enjoyable.

The device is also completely different from anything else released back then, so it looks great on display and always draws attention to itself. No regrets at all about finally adding this to my collection, especially the fact it was my birthday present.

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A new DIY case for the Jaguar Skunkboard

A while ago I put together a small project to flash the Atari Jaguar Skunkboard flash cart from a Raspberry Pi (More details here). The Skunkboard can only hold 1 or 2 games at a time so it was nice to not have to keep removing it and plugging it into my PC to flash it.

Since I built that, I have kept thinking about making it more compact and building everything into a single cartridge. Well, I finally got around to it, and here is the end result:

The cartridge has a DC power jack on the top which is powered from a USB cable. This provides the power to the Raspberry Pi as I didn’t want to risk drawing too much current from the Jaguar itself. The rotary encoder on the side of the unit is used to scroll through the game list and select which game you want and what bank to flash the game to.

I think it turned out pretty well. If you wish to build your own then subscribe to my mailing list from the homepage as I will be uploading the build guide and required files in the new year.

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Commodore PC10-ii

I was given this old PC the other day along with a bunch of other bits and pieces that I am still going through. But this was definitely the most interesting item so I wanted to take a look at it as soon as possible.

After measuring the voltages coming from the power supply it was clearly dead, all voltages shoeing around 1.7Volts. A full re-cap had the potential of bringing it back to life, but these old power supplies were not that great. The huge fan on it also failed and rattled around as it tried to spin.

My decision was to buy a small ATX power supply and retrofit it to the unit. After slicing the connectors onto the modern ATX PSU, I measured all the voltages again and then powered it up.

And it is now booting! This one was actually fitted with an ancient Western Digital Hard Drive which has also died, it spins up and tries to read, but it doesn’t sound healthy and wouldn’t boot. The floppy drives, however, do work, and among the other stuff I picked up, was a set of 5 1/4 inch floppies including a Microsoft DOS Boot floppy.

The most interesting thing about this unit is someone has fitted an Orchid Tiny Turbo 286 processor board to it. I’ve not been able to fully test that yet as I need to build up an AT-XT Keyboard adapter. But the PC does boot with the switch in both positions so I think it’s fine.

The next steps are to fit a modern Hard Drive solution like an XT-IDE board, give it some sound with a modern Adlib Sound card replacement and then design and 3D print a bracket to hold the new PSU in place and mount the power input and power switch on the back of the unit. Should be a fun project!