Another "keys not working" issue
Posted: Thu Dec 27, 2018 4:10 pm
Hi,
I have been getting my (kit built by me) ZX81 working again in the last couple of months.
It has a new sockets for the chips (except the 2114 SRAMs - planning on upgrading to a 16k or 32k SRAM at some point), new Andy ULA and freshly programmed EEPROM. Also a DKtronics replacement keyboard. All buzzed out fine before inserting the chips. Not sure if I have got the NMOS or CMOS Z80 in at the moment.
Using a scope, the video signal is a bit noisy but usable at the moment. Power up gets the K cursor (big relief as well), all the keys work except for some of the shifted keys. For example, all of 1 to 0 keys work but shifted, only 1 and 0 work. Some other shifted keys don't work but there doesn't seem to be a consistent pattern on each row. The display still flickers when say shift 2 or shift 9 (or other combinations) is pressed, just nothing else happens.
The cable between the keyboard and computer might be an issue. It is about 3 metres long so that the computer and power supply can be at the TV and the keyboard be a bit more remote - I don't have a small "portable" TV any more - the smallest being 28" and wall mounted.
Anyone come across anything similar before? Anything to try? I don't really want a shorter keyboard cable but will if nothing else seems to be an option if the cable has too much load depending on what else is shared on the address bus. The scope is an office one, no access until the new year.
I'll cover the video issues when this is one sorted - one step at a time!
Regards,
Dave
I have been getting my (kit built by me) ZX81 working again in the last couple of months.
It has a new sockets for the chips (except the 2114 SRAMs - planning on upgrading to a 16k or 32k SRAM at some point), new Andy ULA and freshly programmed EEPROM. Also a DKtronics replacement keyboard. All buzzed out fine before inserting the chips. Not sure if I have got the NMOS or CMOS Z80 in at the moment.
Using a scope, the video signal is a bit noisy but usable at the moment. Power up gets the K cursor (big relief as well), all the keys work except for some of the shifted keys. For example, all of 1 to 0 keys work but shifted, only 1 and 0 work. Some other shifted keys don't work but there doesn't seem to be a consistent pattern on each row. The display still flickers when say shift 2 or shift 9 (or other combinations) is pressed, just nothing else happens.
The cable between the keyboard and computer might be an issue. It is about 3 metres long so that the computer and power supply can be at the TV and the keyboard be a bit more remote - I don't have a small "portable" TV any more - the smallest being 28" and wall mounted.
Anyone come across anything similar before? Anything to try? I don't really want a shorter keyboard cable but will if nothing else seems to be an option if the cable has too much load depending on what else is shared on the address bus. The scope is an office one, no access until the new year.
I'll cover the video issues when this is one sorted - one step at a time!
Regards,
Dave