Hi all,
The Memotech I bought off ebay arrived yesterday, having re-wired the power supply circuit to run of a Spectrum +2/+3 PSU, the machine powered on.
However with the keyboard connected I could not get anything to appear on the screen, and after a couple of minutes on the display went blank, probing around I found that the -5V line was only -0.5V, on spectrums this is usually caused by faulty 4116 RAM chips, so I de-soldered these, and the -5V was correct again. Fitting sockets and new 4116 chips from my spares box and it now works correctly!
There are now still a couple of minor problems, the colour seems to drift in and out with about a 2-3 second frequency, I guess this may mean that I need to do some work on the video board.
The other is that though the machine is marked as being an MTX512, it only seems to have 32K of ram, it has the half good 64K chips fitted. I plan to remove these, fit sockets and proper 4164s, I have a de-soldering station so should be able to do this cleanly. I seem to remember reading that I'll need to replace the PAL, does an image of the replacement pal's fusemap exist (or even the source to the pal), so that I can program one ?
Cheers.
Phill.
It works !
Re: It works !
Hi Phil,
Good result - well done!
The video problem sounds more like a modulator problem, rather than the video board, but could be either I suppose,
Regards
Dave
Good result - well done!
The video problem sounds more like a modulator problem, rather than the video board, but could be either I suppose,
Regards
Dave
Re: It works !
Could be, though I'm using the direct video out.Dave wrote:Hi Phil,
Good result - well done!
The video problem sounds more like a modulator problem, rather than the video board, but could be either I suppose,
Cheers.
Phill.
Re: It works !
Oooops!
Sorry, obviously not the UHF modulator then, that is quite a common problem, but I should have asked if you were using the TV out - duh!
Regards
Dave
Sorry, obviously not the UHF modulator then, that is quite a common problem, but I should have asked if you were using the TV out - duh!
Regards
Dave
Re: It works !
And the memory is now upgraded to 64K, had a minor glitch as I managed to solder splash the board and connect the cpu /wait line to one of the data lines 
But PAL replaced and PEEK(62122) now returns 1.
Cheers.
Phill.
But PAL replaced and PEEK(62122) now returns 1.
Cheers.
Phill.
Re: It works !
Excellent work!
Glad that you have made good progress
As it seems common for MTX's to be marked / cased as MTX512 , but to have 32k DRAM chips, I wonder if they were suppose to be sold with the 32k memory board.
But if so, where are all these memory boards?
I suppose some of the MTX512's with MTX500 boards may be sold off stock that was not fitted with memory boards due to the money problems Memotech had.
I have a mix of MTX500 and MTX512's. One of the MTX512's has 32k DRAM's on the main board plus a 32k memory board fitted.
The other MTX512 does use 64k DRAM chips.
Mark
Glad that you have made good progress
As it seems common for MTX's to be marked / cased as MTX512 , but to have 32k DRAM chips, I wonder if they were suppose to be sold with the 32k memory board.
But if so, where are all these memory boards?
I suppose some of the MTX512's with MTX500 boards may be sold off stock that was not fitted with memory boards due to the money problems Memotech had.
I have a mix of MTX500 and MTX512's. One of the MTX512's has 32k DRAM's on the main board plus a 32k memory board fitted.
The other MTX512 does use 64k DRAM chips.
Mark
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Not as many MTXs as Dave!
