Yes - there is one of those!
Does it need refitting / replacing? I think I read somewhere that they were added to fix various issue with I/O.
Yes - there is one of those!
Thanks to them for the suggestion and to you for passing it on.RWAP wrote: ↑Wed Sep 27, 2017 6:41 pm It has been suggested on Facebook (as posts are automatically copied to the ZX81 group there) that : "Somebody with an account please suggest to them that it's either the pullup resistors on the keyboard data line socket, or the diodes on the keyboard address line socket"
On the resistors, first, it's R65 to R69 (caught out by yet another error on that schematic ). The resistors are 10k ohms, but because they are being tested in-circuit, the result will be lower. On the issue 2 board that I have to hand, I get about 6.4k ohms with no membrane fitted. As long as they are all very similar, the value is not too important.Lardo Boffin wrote: ↑Wed Sep 27, 2017 11:02 pmI checked R65 to 68 (have not found 64 yet) and got a reading of around 4.1 on each when on the 20k test setting. This was with the COM lead on the right hand leg as you look down on the motherboard.
I checked D1 to 8 and all gave 1 when connected COM to the left leg (looking down) / red to the right and around 0.68 to 0.69 the other way.
Not sure what the numbers mean (noob alert) but they are pretty consistent.