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

Hi,

I am new to the memotech MTX having wanted one since I was a kid just because it looks cool

Last August I got a non working MTX512 and it wasn't until this week that I managed to get a power supply (funnily enough labelled MTX500 for reasons below).

I only had to replace a cracked ceramic capacitor in the machine being the only obvious fault before powering it up. On power up I was happily greeted with the blue screen and Ready prompt.

However as I discovered this machine only has 32k Ram .

Next test will be to load a program onto it and see how it goes.

Hi and welcome to the forum.

MTX512s either had a full 64k on board or had 32k plus an additional 32k memory board fitted. Many “MTX512” computers found now turn out to only have 32k. Somebody may have removed the optional 32k memory board along the way.

There are various options for adding the extra RAM and/or “disk” storage if you are interested

Regards
Dave

I am interested in at least getting it back up to 64k. Most of my machines get some form of cf or sd card.

Options to do both are :

http://www.primrosebank.net/computers/m ... /cfxii.htm

Or

http://www.nyangau.org/rememorizer/rememorizer.htm

Or, for memory only, the easiest is

http://www.nyangau.org/memcard/memcard.htm

Of course, the more radical solution is to desolder the current RAM and replace it with 64Kbit DRAM chips.

does that not include programming a new PAL or GAL?

Yes, but that's the least of your worries if you try that

See the RAM Repair/Upgrade topics on this page http://primrosebank.net/computers/mtx/r ... epairs.htm

The upgrade is doable but, depending on your soldering skills, a little risky. Andy broke one of his machines doing it and I screwed up one the first time that I tried it, though I subsequently fixed it. With care, it can be done, but the other options are less risky if you are not confident of your ability

Indeed, I'd never use a solder sucker ever again...

Clipping the legs of the chips and then removing them one by one (using angled tweezers) is pretty safe, as long as you are not rough and pull hard. Then just a good, pre-fluxed desoldering braid to remove the solder from the holes. I swear by "Soldermop" brand.

I would personally fit sockets. The best way I found to make sure that they stay put long enough to solder when you turn the board upside down is to use double-sided sticky tape cut so that it lies between the two sets of holes and then press the socket on top.

Soldering the pins after that is pretty simple, just use a fine-ish multi-core solder and ~2mm solder bit. A magnifying lamp or head mounted magnifier with a light is good too as you can tell when you've put just the right amount of solder on the joint.

One advantage of de-soldering rather than clipping legs is, if the 32k onboard is made up of the 3732H part, you potentially have replacements for the video ram.

The trick for replacing a 4116 with a 4164 ties A7 high to reduce the chip to 16k x1 which would in theory work on the high bank 32k chips. Whether the timing of the Oki chips is up to that task is another matter, I've not tried it.

http://www.primrosebank.net/computers/m ... mavram.htm

The ITT VRAM chips are dog slow given their model number, far slower than the 200ns Oki RAM chips.