Just realised the 7438 is Open Collector o/ps. So have tested with a LED in series with 270R and the test LED works OK so 7438 is OK.
The usual keypress creates 2V and 0V at the OC o/ps so looks like high res in the keyboard.
Dismantled and checked out all LEDS - working. Continuity between all +5V keyboard traces and back to pin 16 on SK7 but highish resistance without pressing too hard - about 90R. All the LED connections on the keyboard tail are in bad condition SK7 16,17,18,19,20 and pin1 CAPS LED.
Carefully cleaned LED traces and the contacts on the LEDs themselves. I am dubious about not doing something about the bad tail. Conductive paint or the "alternative connector." The "repair kit" is a one time thing there is no real going back from it as it clamps onto the tail. However once this repair is done I should not be removing the keyboard again but I would like it to be reliable and not have to keep risking disassembly. It does have the advantage that removal of the keyboard is much easier because it just connects to the board via a header and you are not constantly wearing away at the tail. Even so the tail might need trimming because pin 20 wear goes quite a way up.
The second keyboard is in much better shape. Just the very end of the SK7 tail show signs of wear. In both cases the SK6 tail seems unscathed. All the LEDS light but apart from POWER LED quite dimly. Even in a dim room difficult to see. Not a disaster but might disassemble and clean anyway to see if that helps.
Disappointing that Acorn went down the route of dodgy 'Spectrum' keyboard technology .........
The usual keypress creates 2V and 0V at the OC o/ps so looks like high res in the keyboard.
Dismantled and checked out all LEDS - working. Continuity between all +5V keyboard traces and back to pin 16 on SK7 but highish resistance without pressing too hard - about 90R. All the LED connections on the keyboard tail are in bad condition SK7 16,17,18,19,20 and pin1 CAPS LED.
Carefully cleaned LED traces and the contacts on the LEDs themselves. I am dubious about not doing something about the bad tail. Conductive paint or the "alternative connector." The "repair kit" is a one time thing there is no real going back from it as it clamps onto the tail. However once this repair is done I should not be removing the keyboard again but I would like it to be reliable and not have to keep risking disassembly. It does have the advantage that removal of the keyboard is much easier because it just connects to the board via a header and you are not constantly wearing away at the tail. Even so the tail might need trimming because pin 20 wear goes quite a way up.
The second keyboard is in much better shape. Just the very end of the SK7 tail show signs of wear. In both cases the SK6 tail seems unscathed. All the LEDS light but apart from POWER LED quite dimly. Even in a dim room difficult to see. Not a disaster but might disassemble and clean anyway to see if that helps.
Disappointing that Acorn went down the route of dodgy 'Spectrum' keyboard technology .........
Statistics: Posted by Questor — Sat Apr 19, 2025 5:14 pm