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

Hello
I have just brought an "MTX512" from ebay, it was only £52.... good news so far... then I opened it.

Please excuse the following (probable) errors, I have not owned a Memotech before (although have always wanted one since they came out, see my "introduction" for more info).

It seems like I have brought a "bitsa" (i.e. bits-of-this-bits-of-that). I "think" it has a MTX500 32K motherboard as shown here (library picture, not mine)...

And a memory card (not sure how big, probably 32K? if anyone can tell from my pitures, link later, please share!) as shown here...


There is no ribbon cable between the (loose) keyboard and motherboard, and no 4way ribbon cable from the video connectors as shown in the first image.

There is no PSU included, but after looking at some very helpful sites, I have decided to use a DC PSU and some dc-dc converters (ebay again) they are cheap (http://www.ebay.co.uk/itm/151311737680) and trying them, they seem very good.

It does have some free authentic cobwebs, every cloud

If anyone is interested, I have uploaded some pictures here...

http://1drv.ms/1MNRNXd
http://1drv.ms/1BTSIjX
http://1drv.ms/1BTSTvF
http://1drv.ms/1BTSZDF
http://1drv.ms/1BTT7CQ

Regards



Matt

Hi,

nice photo - mmm, where have I seen that before ?

your machine looks like a pretty common "MTX512", made (by Memotech) from an MTX500 computer board (32K RAM) with a 32K memory expansion board soldered to the internal edge connector.

It's a pretty common configuration

http://www.primrosebank.net/computers/m ... yboard.htm
http://www.primrosebank.net/computers/m ... spares.htm
http://www.primrosebank.net/computers/m ... _video.htm
http://www.primrosebank.net/computers/m ... mtxpsu.htm

regards
Dave

The MTX needs a +12V, +5V, -5V and if you get a RS232 serial board, -12V supplies.

Most of the logic is powered from the +5V rail. I suggest you use a supply rated at 1.5A.

The 16k video DRAM chips need a +12V supply (main supply rail for them) and a -5V bias supply. If the -5V is lost, or not present, these DRAM chips can die. IIRC, some of the audio circuitry uses the -5V supply as well.

The plug-in video board also uses the +12V supply.

Mark

@ Matt - is it your intention to have a power supply arrangement that replaces the on-board voltage regulator circuitry, or are you intending to supply voltages suitable for the on-board voltage regulator circuitry input terminals?

You may want to have a read of this thread: Building a replacement MTX PSU

If you want any more details, let me know and I will go and dig out the details.

Mark

The keyboard cable is easy to replace, one "side" of a 40 way IDE cable does the job. Likewise the PAL board to MONITOR/"Hi-FI" ports is easy enough top make up.

http://primrosebank.net/computers/mtx/p ... _tu_nd.jpg

The PAL code on your memory board is 0LL
0 meaning it's programmed for a MTX500 with no other memory expansions.
the L's signify each of the 2 banks of chips expects a 3732L (as opposed to 3732H)

If you could find 8 3732L's the ram could be expanded from 64k to 96k, although there's no real benefit in doing that unless you use large arrays in Basic, as the former commercial software available is all for the 32k or 64k systems.

It might also work with 4164's though I've never tried it.

Mark will it be possible to buy one of your replacement psu's ?
Maybe can be ready for next memofest ?

1024MAK wrote:@ Matt - is it your intention to have a power supply arrangement that replaces the on-board voltage regulator circuitry, or are you intending to supply voltages suitable for the on-board voltage regulator circuitry input terminals?

You may want to have a read of this thread: Building a replacement MTX PSU

If you want any more details, let me know and I will go and dig out the details.

Mark

Of course you can buy one.

It will take me a while to build it.
Hopefully April will be a bit less busy than the last three months.

Mark

Dave wrote:Hi,nice photo - mmm, where have I seen that before ?

Likewise, looks just like my old MTX512 - even down to the scratch on the far right of the base