Malfunctioning VT240 - help please

Adrian Graham binarydinosaurs at
Thu Jun 11 13:37:17 CDT 2020

> On 11 Jun 2020, at 15:14, Charles via cctalk <cctalk at> wrote:
> =========
> Thanks for the tip. I didn't see in the manuals that the keyboard light pattern was actually a binary code, but that makes sense! I would have expected an error message on the screen, but as I previously noted, the video system itself does not seem to be working properly.
> Unfortunately my logic analyzer is an ancient Tek 7D01, the equivalent of stone tools rather than metal ;) It's not really suited for doing this kind of work, but it's what I have... I wonder if anyone has already disassembled the code?
> The 4116's are soldered to the board, too. Since the memory map is shown in the tech manual I could write a simple memory test and burn an EPROM.
> My fear is that one of the PALs has altered itself from tin-whisker migration (fuse regrowth) :(

You’ve just mentioned the magic 4116 word, I’d bet some of your dollars that it’s either one of those that’s gone south or the -5V required to run them

Adrian Graham
Owner of Binary Dinosaurs, the UK's biggest private home computer collection?
t: @binarydinosaurs    f:

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