Category: Accessory

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Yamaha DX-7 Repair

Recently, a colleague at work contacted me and asked if I wanted some old computer stuff, including a 19″ CRT monitor and a colour Dot Matrix printer. This donation was gladly accepted, and whilst collecting my new toys, we found ourselves discussing various retro tech.

During this conversation, he mentioned that he had a Yamaha DX7 synthesiser that he had purchased, but it had a fault. It is very common for the batteries to die on these, which then leads to corrupted content in the RAM. In this case, though, the battery had already been replaced, but it didn’t fix the issue.

I did a quick Google search for the schematics, and essentially what I saw were the schematics of an 8-bit microcomputer. I said I’d take it back with me and take a look to see what was going wrong. Occasionally, the keyboard would appear to boot up, but would then hang, other times, the display would be garbled and completely unresponsive.

I knew the CPU was trying to run code because the display was occasionally showing correct text. Just to rule out a ROM chip issue, I downloaded the ROM file from the internet and compared it with the ROM stored on this chip. All looked ok, but I wrote the ROM to a new chip anyway and tested with the same result.

I then grabbed my scope and started probing the pins on the ROM chip to see what the address bus and data buses looked like. It was with the scope that I saw the issue, or at least the first issue. The data bus pins were all looking good with nice strong 5V peak-to-peak signals. But the first 8 address bus pins (0 to 7) were all a lot lower. Address bus pins 8-15 were all working as expected.

I dragged out the schematics and did a quick glance around for something that was only connected to the first 8 address bus pins. There was one very obvious candidate, a 74LS374 transparent latch IC that sat between the address bus and the ROM chip. Looking at the inputs of this IC showed they were nice and strong with no issues, but all the outputs were low, as shown in the picture above.

I suspected that this chip was faulty, but it could still be another IC on the board pulling the outputs low. So to test for that, I snipped one of the output pins so it was floating, then measured again. Exactly the same issue. At this point, I then removed the IC from the board, ready for the replacement chip to arrive.

Now off the board, I tested the chip in my chip tester just out of curiosity. It did indeed state that the device was faulty. I will be testing the new ones when they arrive, as I’ve not used this chip tester before, so not sure how much trust to put into it yet.

All I need to do now is await the delivery of the new IC and hopefully, this classic synth will be back up and running again. I will of course update everyone with the result, and hopefully this is the only fault 🙂

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Sam gets a mechanical keyboard

Although the keyboard on the Sam is quite nice to type on, you just can’t beat the feel of a hugh quality mechanical keyboard. Luckily for me, Colin at Quazar builds a lovely mechanical keyboard for the Sam and this evening I got around to fitting it.

The install process is pretty simple, it just plugs into the original keyboard slots and then you just swap over the original key caps.

I went for the slightly clicky keys as it’s what I prefer, but he does give the option of quieter keys switches also.

It’s a really nice product, especially if your Sam’s keyboard membrane has either broken or starting to wear out. I’d highly recommend it 👌

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Sega Mega CD

I’ve always wanted to grab a Mega CD but the prices have always put me off. But recently I came across a listing for a Mega CD that was “not powering on” for £100. After previous research, I believed this was likely due to the pico fuse gone in it as is common on these units. So I decided to take the chance, and sure enough, after replacing the fuse it came to life. I’ve since replaced all the capacitors in it also as these are prone to failure in these units too.

Now I’ve gone this far I guess the 32x now has to be added to my shopping list!

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Vectrex gets a splash of colour!

I’ve had the Vectrex for a while now but didn’t own any original games for it. I started by using a multicart and then moved on to the Pi-Trex.

The issue with this is the original games used to ship with colour films that fitted over the screen to add some colour to the vector art. That issue is now a thing of the past as I have not only purchased my first original game, but also purchased a pack of 9 original overlays from one of the retro Facebook groups.

So here for your viewing pleasure is Scramble running on the Vectrex with its matching overlay!

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Gamecube Gameboy Player

Rather than a new console, this update is for a new accessory. The Gameboy player, as it suggests, allows you to play Gameboy/Color/Advance games on the Gamecube.

I picked this up from eBay for a reasonable price as it was the unit only without the required disc. But since my Gamecube is modded I can run the GBI software instead which is a community version of the player software and is apparently better in every way anyway.

The unit sits underneath the Gamecube and utilises the ports on the bottom of the Gamecube. A very nice subtle upgrade.

Now when the batteries run out on my Gameboy Advance, I have the option of switching to the big screen and continuing my game from where I left off. The picture quality is also pretty good coming through the OSSC and into the plasma TV in the bedroom.

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Dk’tronics Spectrum keyboard

When I was younger we had our 48k Spectrum in a big black plastic keyboard shell. So I didn’t have to put up with trying to type on the little rubber keys that people normally associate with the Speccy 48k (This was before the Spectrum+ came out).

For a while, I have wanted to get one of these again as I have no idea what happened to ours. I think it’s probably sat in a loft somewhere well and truly buried!

Well, I finally managed to get one, and it’s also complete in its original box. Not only that but it appears to have never been used as the stickers for the keys haven’t even been applied yet.

Of course, you know what the next problem is. Do I actually use this and apply the sticker set? Or does this one need to stay in its current condition and I now need to buy another one to actually stick a speccy inside!! 🤣

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Sam Coupe HDMI Interface

Some of you may be familiar with RGBtoHDMI project (https://github.com/hoglet67/RGBtoHDMI) Which uses a raspberry pi board to convert the RGB signals from old computers into a HDMI signal for modern TV’s.

It was originally designed for the BBC Micro but was then extended to include other computers such as the Spectrum and the Amiga.

I popped over to the GitHub one evening and posted a message to see if in theory, the project would work with the Sam Coupe. A couple of messages later and IanSB had already implemented theoretical Sam support into his fork of the project.

So my next step was to build up one of the 12bit boards and wire it up to the Sam to see if it worked. And it did!!

It all powered on first time and the picture quality was absolutely perfect. All I had to do was center the image on the screen.

Once I had proven it was going to work I then made a prototype of the interface board that would connect this up to Sam. I am planning on designing a proper PCB for this part now it is all tested.

I then knocked up a quick case design in Sketchup and printed it out on the 3D Printer to give it a slightly more professional look. I even fired up the Vinyl sign cutter to give it a Sam style logo 🙂

And there we have it. The worlds very first (As far as I know) Sam Coupe HDMI Interface! Once I have the PCBs made up I’m probably going to build up a few of these as there are a number of people interested. But I will be releasing all the files so anyone can construct their own as I don’t want to spend the rest of my life soldering boards and the SMD components on the RGBtoHDMI board are a bit fiddley. Hopefully, I will get a bit better at them the more I do 🙂

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Roland MT-32

Back in the days of DOS-based games and mainly point-and-click adventures, when you set up a game you had to choose your soundcard. Most people had a Soundblaster Compatible, some had the Adlib soundcard. However, there was also an option of the MT-32 or MPU401. I didn’t know anyone who had one of these and for good reason, they cost around £500 back in 1987 when they were released. I remember paying around £50 for a Soundblaster card and CD-ROM drive so the cost difference was quite substantial!

So what made it so special? Will the MT-32 is a MIDI Device that was connected to your PC via an MPU-401 hardware interface. This gave your computer access to the audio hardware that most of these tunes were actually written on back then. Songs like the theme tune to Monkey Island were actually composed on the MT-32 and therefore you would get to hear the music exactly like the musician intended it to be heard.

So after seeing some videos about this device, I knew I needed one in my collection, and it really doesn’t disappoint. Listening to Monkey Island, Day of the Tentacle and Simon the sorcerer though this module adds a whole new atmosphere to the games.

I will do a write up on this soon. I will also put up some videos showing it working, and the difference between this and what we had to listen to back then.

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Greaseweazle F7 – Retro USB Floppy Writer

One issue people have these days is writing floppy images back to 3.5inch floppy disks so they can be used in retro computers such as the Amiga, Sam and Atari ST etc.

The first mistake people make is they just go out and buy a USB floppy drive. The problem is these devices don’t give direct access to the floppy drive hardware so none of the applications designed for this purpose work with them.

So now you have two options. You can either put together an old PC which has a floppy disk interface on the motherboard (I do already have one of these for this purpose). Or you can buy yourself a Greaseweasel interface! This interface links to a modern PC via USB and then connects up to an old flopppy drive. Combined with the software available from here: https://github.com/keirf/Greaseweazle you will now be able to read/write and format floppy disks in the correct format for retro computers.

I have designed and 3D printed a nice enclosure for this to all sit in which can be downloaded here if you want to print one yourself.

I purchased this device directly from Kier and it cost me £22 inc postage to the UK which I think is a brilliant price for a device that is going to be very useful for any retro computer collector. Head over to his Facebook page to find out more information on how to purchase one.