Wanted: broken motherboard!
Does anyone have a motherboard for a 48k (any issue) that is currently not working? I'm looking to set up a test board for chips, and would like to get hold of one that I can socket throughout.... If you have a board that is not working, for a reasonable price, do get in touch!
Post edited by Simon_Carr on
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I have plenty, but planned to disassemble completely because these have complex problems - I only do this when I spent enough time on them already: after testing ram, Z80, ula, power circuitry etc.
So that is not what you want ;)
But what I wanted to say is that when you want to test upper memory (4164) chips, you are better of using a +2 or toastrack board, as in a 128K the complete chip is used (in 48K only the half).
I use a 48K issue 3 board for 4116 chip testing, and a +2 board for 4164 chip testing.
And of course Paul Farrows diag rom.
In the future, I'd like to get hold of a toast rack to add to my collection, as I think they (combined with the QL) were the final grand designs of Sinclair before Amstrad turned the spectrum into gaming consoles!
I guess my main focus for testing is on the 48k machines, which seem to the most common, and will probably be my main thrust for repairs and spares in the future.
Everything goes on hold though now for a few weeks, as the new academic year starts soon, and I have loads of teaching prep to get done. My poor spectrums have barely been switched on recently!
Still be aware that the 4164/4532/3732 chips in the 48K are only used a half.
To test the chips fully, you will need to switch between the 'L' and 'H' connections which ard hard wired on the board by default.
A toastrack or +2 will test both halfs.
As you may know I sell hundreds of new old stock 4116 and 4164 chips.
The 4116 are all tested in a 48K board with all 4116 chips socketed.
The 4164 are all tested in a +2 board with higher memory chips socketed.
One of about every 20 chips fail, so it's wise to test them, allthough I buy them as new (old stock).
In a +2 there are two rows of 4164 chips.
The upper row is high memory and 128K pages, D0 to D7 from left to right.
The lower row is lower memory and some pages, D7 to D0 from left to right.
I don't test 4164 chips in the lower row as I can't determine which chips is faulty easily there, so only the upper 8 chips are all socketed.