Started by ikonsgr, 00:21, 02 August 22
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Quote from: pelrun on 11:09, 02 August 22IC's are sensitive to electrostatic discharge? Why didn't someone tell me earlier? It actually takes a lot of engineering work to make any device robust against casual ESD events. Cheap home computers from the 80's... have exactly none of that. The CPC's joystick port is especially egregious because it exposes floating CMOS pins directly to the outside world.If you instead look at something like the Amiga schematic, the joystick port has ESD diodes and current limiting resistors on all the lines. The CPC just uses wires
Quote from: ikonsgr on 11:02, 03 August 22Some update: As i have a complete "rebuilded" cpc6128, with all ic's on sockets, i removed the bad AY3 from cpc464, solder a socket, and plug the good AY3 from cpc 6128. The "always active" column problem, seems to resolve, as i dont get any characters on boot. BUT, now i have an even more weird problem: many keys pressed, return 2 characters on screen! I checked with the keyboard matrix, and found out that, for every key pressed, the one that coresponds to same column and previous line, is also activated and printed on screen! For example, if i press 'R' which is on row 13 ,i also get an 'E' which is on same column, but on row 12! Same thing happens with all keys (except the one that in the 1st row). Does this mean the 74ls145 needs replacement too, or you think it's also PIO chip damaged too?
Quote from: Rabs55 on 14:09, 03 August 22Guessing here as new to this but, if you press 'E' do you also get 'R' (other way round to your example)? i.e. is there a short between row 12 and 13 at the 74LS145. Worth a continuity check.
Quote from: ikonsgr on 14:45, 03 August 22Quote from: Rabs55 on 14:09, 03 August 22Guessing here as new to this but, if you press 'E' do you also get 'R' (other way round to your example)? i.e. is there a short between row 12 and 13 at the 74LS145. Worth a continuity check.If i press 'e' i also got 'esc', and same goes with any key pressed, i also get on screen the corresponding character of same column and previous row in keyboard matrix!If i press 'O' i also get 'U', if i press 'H' i laso get 'G' and same goes with ane key! It's like 74LS145 decoder gives double signal or maybe the the 4bits of portc from 8255 I/O chip gives wrong signals?
Quote from: Audronic on 01:33, 04 August 22@ikonsgr Is the replacement chip AY-3 8912 or an AY-3 8912a
Quote from: eto on 14:31, 04 August 22Does this happen for all rows, or only for some of them? What happens, if you press a key from line 0?
Quote from: eto on 14:31, 04 August 22When you press something from line 6 or 2, you get something from the line above, line 7 or 3, right?
Quote from: eto on 14:31, 04 August 22What about line 5? Is it the line above, 6, or does the response come from line 4?
Quote from: Audronic on 01:36, 05 August 22@ikonsgr ? do you have a Joystick connected during the testsKeep SafeRay
Quote from: ikonsgr on 17:58, 12 August 22Ok, i've just replaced 74LS145 and 8255 I/O and still i got the same symptom! Any key pressed, will type the character pressed and then the character on same bit next line!Is there a chance that the rom might be damaged too? I really can't think anything else...
Quote from: Rabs on 18:04, 12 August 22Hi on one of the 464s I repaired with an odd keyboard problem, it turned out to be the ribbon connector on the pcb. Give it a good clean and then clean it again. Hope this helps.
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