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

So having offered to try and fix some of Jim's kit over the weekend, I thought I'd better at pretend to tidy the "operating theater", so there's at least -some- space to work... Now to await the patients!

Looks ready, Martin!

I hope you have great success with Jim's repairs.

Have a great time everyone.

When you see the amount Jim brough it's a wonder the car's suspension didn't collapse!

So we got off to an early start wading through the boxes of bits while we partook of a late lunch. Pictures from Jim's phone.

The easy bit was a ROM update to Jim's MFX which is fitted in the gorgoues red MTX.
The 4 rom, rom Board was confirmed to be a working Newword rom board

3 of the 4 ram boards tested out as probably working, including one that reports as 128k ram for the MTX 512, I cant say I've seen or heard of a 192k ram MTX with original hardware before. There was one 32k board that doesn't work, to be looked at later if there's time.

2 dodgy MTX main boards were looked at, and MTX 500 and and an MTX512-S2

The S2 appears to have no working ram, my system diagnostic board (that runs without ram) confirmed that pretty much the rest of the board is fine. CPU, VDP and keyboard tested as good. That's slated for further dissassembly tomorrow to check the patch wiring from the S2 conversion is OK, as replacing the memory decode PAL had no obvious beneficial effect.

The 500 was completely dead, replacing the CPU at least showed the hearbeat on the test board, but still no output. The VDP was tested in the other board as good. Current thoughts are maybe something in the I/O decode is at fault as the VDP doesn't appear to be getting any chip selects. More testing and possibly chip replacements for that board We had the excitement of an exploding capacitor on one of the 5 1/4 drives brought for testing. The SDX interface board appears not to have suffered any ill effect thankfully.

Bloody hell, that's a lot of kit to get through. Good job you've got a ham sandwich to see you through.

Not sure I approve of the early consumption of mince pies. It's not even December yet man!

gunrock wrote: ↑05 Nov 2022 08:17 Not sure I approve of the early consumption of mince pies. It's not even December yet man!

The best before date was early November, we couldn't let them go off could we...

First job of the day:
Videowall MTX with apparantly no ram opened up, and there just to the right of centre in the photo, was a patch wire off! A new bit of solder and a larger stripped area on the wire and everything is back together as it should be, and will hopefully stay that way.

Exhibit A
256K MTX S2 working

Looks like the doctor is in. I would love to have been there this year as I've not had much to do with MTX of late. There is always next year.

Seeing a working videowall would be amazing I'd have to say. Thanks for the updates.

Paul

And there was cake.

With Megastar games themed decoration. PS yes the bread at lunchtime was freshly baked too.

I’m safely home after another adventure in St leonards on Sea

We identified a read line (/RD shorted to 0V/GND) control fault with on one MTX. But did not manage to locate where on the board the problem lay, other than it’s not any of the chips. The resistance between the /RD line and 0V/GND is about 16 ohms, which is really low. I suspect a solder splash under one of the IC sockets, either the PAL or the CTC.

The second MTX has the Z80 being lazy, only the control pins and address lines A0 to A7 are doing anything. It won’t even run Martin’s diagnostic board
Another Z80 did not improve matters, nor did removing any of the socketed chips. Bad light stopped play…

Mark