General Stuff(tm)

[PhilC]

Just fired the Lynx, and it boots with a singular beep and you get the Lynx logo and prompt.

Then the power supply has started making noises and it keeps losing sync. Typical old computers, know what I'm fixing this afternoon.

BTW, you can borrow the Lynx if its of use to getting the others working?

Edit: Wasn't the PSU making the noise, it was the speaker They were right next to each other.

Just pressed the socketed chips back in and off it went again.

[stephen_usher]

Thanks. Apparently in 48K mode it beeps once and in 96K mode it beeps twice.

The RAM refresh issue is due to the system using the Z80's refresh which only does 128 rows and not 256, which all the TI chips need. Older 4164 allowed 4116 compatible refresh cycles.

I'm still not getting anywhere with the keyboard issue. From the hardware point of view everything looks fine. I've put some pull-ups on the keyboard read lines which has helped what they look like when a key is pressed but it made no difference. It's almost as if an I/O read isn't happening now and again. Maybe it's a timing issue?

[PhilC]

Ah I see, I need a third eprom, will see if I can find and burn that.

[PhilC]

I've put the three 96K roms in and can confirm it does beep twice on boot.

[stephen_usher]

Thanks.

The machine seems to be running happily in 48K mode, other than the keyboard issue. I've managed to load the game "Star Trek", which is mostly BASIC, so the tape interface definitely works.

With respect of the keyboard, looking at the ROM source (https://github.com/w5Mike/Lynx-Rom-Anal ... 8k_Rom.ASM) I can't see how it can not work other than if an "in" is not returning the correct value.

[stephen_usher]

I've ordered a 74S138 from Mouser, along with 500 decoupling caps to make it half worthwhile.

I have a feeling that the 74LS138 is marginally too slow for the keyboard read timing and the CPU is reading zeros on random lines on the bus.