Re: Another Gigatron TTL in Finland
Posted: 12 May 2022, 06:51
The non-working project. I have put good effort try to fix this, but no function yet. Last try will be use troubleshooting.xlsx to find where faults occur.
A place for Gigatron builders and hackers
https://forum.gigatron.io/
The BAT42 diodes are fine, only faster. It is possible that the resistor packs near the diodes are lower in values too. The diodes (and resistors) shouldn't affect the keyboard. The keyboard not working shouldn't be normal since you did indeed replace the missing shift register. So maybe you weren't getting enough power, or maybe the shift register you got from the first machine was bad.veekoo wrote: ↑17 Jul 2021, 16:36 I had to try to make a DIY kit from budgetronics. Lack of skills probably didn't get it all working so ended up using it as spare.
I ordered second one "Fully Assembled Gigatron TTL" from ebay and got it at reasonable price. When it arrived it was missing U39 serial input IC and another mail was coming with 74HCT595 later on.
Well I had the spare parts and took SN74HC595N, I was able to get blinkenlights, power on led, startup sound and main screen booting.
Long story short I had 3 keyboards at what 2 seemed compatible with PS/2 standard and I tried them but nothing happend. No signal lights at keyboard otherwise system seemed ready to accept commands.
Seller said it seemed normal operation because of missing the right IC chip and my chip needed 1N60P diodes and the board had BAT42 instead. Actually diodes looked pretty much the same as in my failed pcb.
Probably in question is some signal level matching or timings what I understood. Seller seemed sure of things so I have meen mostly waiting customs to send me my letter.