*** M E M O R U M ***

The CFX II+ latest development:
Thanks of course to Bill, Dave and Martin for some great work with this

Mark

Hex-Train+, yet more wonderful work from Andy

Mark

(See Andy's site for more details...)
More, you want more? And I don't just mean the cake (one of three cakes, mind! Yum!).
Well Andy's event report is here Better yet, come to the next Memofest

Mark

So last thing Sat, after everyone else had gone, Mark and I had a look at Paul D's MTX to try and work out why it was having video issues. By the time Mark had to leave for the long drive we still hadn't duplicated the fault, even with the extra load on the PSU of driving a CFX-II on the expansion connector.

Still I was able to get a shot of the MTX driving 3 separate screens Sunday morning before Paul was due I had a further play with the board before Paul arrived to collect it on his way home.

It looked like one of the capacitors on the Video Daughterboard could possibly be shorting to a via on motherboard. Once small piece of insulating tape later the potential short was history. An hour long soak test and still no problems so hopefully that's one system fixed at least for now.

The 2nd repair booked for Sunday Morning was Jim with his red MTX. Which had no display.

We connecter it up to the monitor, and as expected the display was blank. However in order to know whether we had a black screen which is a common fault, or a blue one we connected the old TV. Which produced a flashing cursor and "Seady" and a few random exclamation marks on an otherwise working display. We swapped the daughter board and then on the next re-boot had the same display on both screens.

An close examination of Jim's daughter board provided the answer. The was no link in either of the 2 jumpers that allow colour or mono composite output. Fitting one link solved the missing display problem.

I plugged in the CFX-II board so that the start-up screen would give us a display to help diagnose the corruption of "Ready" into "Seady" and it was obvious that the lowest bit of the display ram wasn't outputting correctly. The Circuit diagram suggested this should be the chip in location G4 which we confirmed with a 10R resistor grounding Pin 14. That chip came out and was replaces with a socket and one of the re-cycled 4116 chips from the spares box. Video corruption solved.

Next up was fitting the Magrom internally and a "test" of some of the games.

That revealed a 3rd problem the "H" key didn't work. Changing the cable didn't change anything so we connected my keyboard, that worked as expected, confirming the motherboard was fine and that the issue was the keyboard itself. Experimentation confirmed it wasn't just the "H" key, but also "F" Cursor right and a few others. All keys connected to the same pin on the keyboard connector. Tracing with the meter confirmed a break in between the connector and the first of the keys connected to it.

Being a Memotech, that required a yellow wire to restore connection. With (hopefully) everything now fixed we were able to test the Magrom and confirm for now at least the Ultra Rare RED MTX WoW!! is working. Anf JIm was finally able to head for home with his repaired MTX and A large chunk of the Pothole Pete themed cake as souvenirs of his trip to the South Coast.

Mark poster a picture of a home made keyboard with a suggestion it might have been a cake. Of course it's not, Pothole Pete was the real cake.

The home made box hides a component reduces sort of MTX like system, one of a couple of experiments I'd tried with the intention of making a replacement Main board using more modern components.
Under the cover is a Z80 running at 9.8304 Mhz (the odd speed is a consequence of the requirements of the serial connection), memory, CTC, SIO and serial to USB adaptor, plus the various support chips. On the other side of the connector is a propeller video display from the CFX built onto a MTXplus compatible connector.

In theory it could run MTX basic, however it would need the display handler re-written. With only the 80 column display it's really intended to run CPM. Which it will, using the same disc images as the CFX and CFX-II, booted from a modified CPM rom.

Over all though it's still too big to fit the mounting rails under the keyboard in a real MTX. More work needed!

Sorry, just got to say again.. that red MTX is the sexiest 8 bit machine full stop. I could sit and stare at it all day. No, really!

JonB wrote:Sorry, just got to say again.. that red MTX is the sexiest 8 bit machine full stop. I could sit and stare at it all day. No, really!

Jim can sit and play games on it all day now hopefully!

seems like a few mtx's was fixed too cool

Thanks guys for another great event, hope to join it next year, if some one want to host it....

1024MAK wrote:The CFX II+ latest development:

Thanks of course to Martin and Bill for some great work with this

Mark

No mention for me then