ROMBO Redux Deluxe - New ROMboard

Started by The Equalizor, 15:28, 08 July 18

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Bryce

Quote from: The Equalizor on 14:18, 30 December 21
You're welcome Peter,


All I gotta do now is try to work out why the boards won't work reliably on the Plus machines. I might see if @Bryce can help me with this. It's very odd as the board initialises okay but crashes when you start issuing ROM commands. The chips are 74HC which are the correct ones for both Plus and CPC compatibility but they just don't work.


Maybe I can bribe someone knowledgeable with a free one if they can work out the Plus issues with me.


Regards


Rob
Hi Rob,
         have you changed anything significant since the board version you sent me? I have used the board a lot, but not on a plus. I can set it up later and see if it works or has issues on a plus if you like.

Bryce.

The Equalizor

Hi Bryce,

Thank you for the offer but I've actually fixed the problem.

It was caused by an incorrect pullup resistor that should have been 680ohm but was 1K on the board. This is the Resistor that is at one end of the 1N4148 and goes to 5v for Pullup and ROMDIS on the Expansion connector and the 74HC27.

This doesn't affect standard CPC's (purely by luck, or rather hysteresis) but I guess the Plus machines are more fussy.

This issue was caused by me sticking a 1K placeholder resistor in the Schematic that I was supposed to remember to change but, well, I didn't, so when the parts went across to the PCB it took the 1K designator with it.

If you want to fix this yourself, just change out the resistor that's next to the 1N4148 Diode under Socket 2 of the board to 680R.

Regards

Rob

Bryce

Quote from: The Equalizor on 18:11, 31 December 21
Hi Bryce,

Thank you for the offer but I've actually fixed the problem.

It was caused by an incorrect pullup resistor that should have been 680ohm but was 1K on the board. This is the Resistor that is at one end of the 1N4148 and goes to 5v for Pullup and ROMDIS on the Expansion connector and the 74HC27.

This doesn't affect standard CPC's (purely by luck, or rather hysteresis) but I guess the Plus machines are more fussy.

This issue was caused by me sticking a 1K placeholder resistor in the Schematic that I was supposed to remember to change but, well, I didn't, so when the parts went across to the PCB it took the 1K designator with it.

If you want to fix this yourself, just change out the resistor that's next to the 1N4148 Diode under Socket 2 of the board to 680R.

Regards

Rob

Well done! Now you've learnt the difference / importance between a pull-up and a weak pull-up. Always use the same value (or slightly lower) pull-ups as the system that you are interfacing to, otherwise you'll encounter the issues that you had and it'll mess up your day.

It's always better to discover these things by real life experience. You can read about it a thousand times, but you only really learn it when you experience it for yourself. Glad you got it sorted.


Bryce.

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