exxos's Atari, Amiga & retro forum

stephen_usher wrote: 29 Mar 2026 21:50 Yeah, well, I'm going to be using Chinese knock-off ones as they're massively cheaper and I don't think the machine will get a huge amount of use. :-)

Yeah, I think that's most people these days, me included.

So how much is left to do? I may consider one myself depending on how well yours goes :)

As you know I like a bare board computer :)

Well... FedEx finally turned up at 3:30pm. So much for the "AM" delivery as written on the label.

Put everything on the board, then found I'd only ordered one LS166 instead of three. Never mind, that's only for the RGB channels and I'm attempting to use composite at the moment.

Switching on... Overcurrent at 800mA... Had to up the current limit beyond 1A on the 5V rail, but only if the clock divider chip was installed, otherwise without a clock it was ~700mA.

On the screen... either black screen or white screen. Not a lot happening on either then main RAM or VRAM banks, just a few FFs on both on the Data Out pins. More on the Data In pins on the VRAM.

Found that A0 and /RAS had a phantom ~1 ohm short on the main RAM. Couldn't find it. Washed the bottom of the board and scrubbed with a brush. Removed all the RAM... all looked fine. Washed and scrubbed a bit, the resistance changed. Scrubbed on the top of one socket, which looked very clean and the short disappeared!

Still getting nowhere though.

The problem is that I can't guarantee the ROM images are correct. I found them in the MAME archive, so they could be hacked to death and I wouldn't know. I'm also having to duplicated them four times. It could be that I need to byte swap them too. I don't know!

@stephen_usher I think the name stuff needs byte swapping from memory.

I did find some rims online but didn't save the link. If it's of any use, I may be able to read the rims from mine but it's obviously the 48k version, so not sure if it will help or not?

Edit: ignore me, see next post :lol:

I'm an idiot! I needed to replicate the images 8 times, not 4 to fit on a 27C512. D'oh! No wonder it was only reading FFs!!!

After writing the correct number of copies and reburning the ROMs...


Yay!

Now need to wait for the LS145s to arrive and then I can build the keyboard as all the MX-ish key switches and key caps arrived from China today.

:girldance:

Other than the 145 the keyboard is "finished".

Looks really good !

Just need a proper case now.

HigashiJun wrote: 02 Apr 2026 00:03 Looks really good !

Just need a proper case now.

Yeah. I'm going to have to design and 3D print one.

It turns out that I do after all need the 12V supply not only for the serial port, which I'm unlikely to use, but also the TEA1002 PAL encoder chip so as to get colour composite output.

So I've changed the power input on the plug and lashed up a buck regulator to generate the 5V supply.

Unfortunately the cheap Amazon regulator is a bit wobbly on its output so I had to fit a 2200uF cap to smooth the supply.


Not pretty but it will do.

I'll also have to get an inductor for the board as I thought I'd be able to do without it but the colour clock is so noisy that it really needs that filter.

So, current state of play:


Not working:

Cassette interface: Due to not being able to get a 7 pin DIN socket with the correct footprint.
Full colour on RGB: Missing two 74LS166 chips for the Blue and Red channels.
Colour composite video: Missing 10uH inductor to filter out high frequency noise in the oscillator circuit. This should arrive this evening.
Sound: Missing speaker. Due from Amazon this evening.
Keyboard: Missing 74LS145 chip.

Working:

As far as I can tell given the above, everything else.

I've had to put heatsinks on the buck regulator switching transistor, coil and input capacitor as they were all getting burning hot. Obviously 1A is at the very limit of this device which was marketed as being capable of 3A. What do you expect from Amazon stuff, being like AliExpress but with faster delivery. I'm not sure how long it will last.

Anyway, after this evening I won't have a chance to do anything until after the Bank Holiday period.

19:20: P.S. Speakers have arrived. Sound works.