+slx Posted October 10, 2017 Share Posted October 10, 2017 I bought an (otherwise working) PAL 800 on EBay which has a dead Mitsumi keyboard. The seller claimed he had tried it with a "brand new" keyboard and had had no success either. I have swapped the POKEY with a known good unit from a 400 with no effect. The Pokey from the 800 seems to work in the 400 (keyboard registers, I didn't test beyond that). Are there any other auxiliary chips swapping of which might help in identifying the cause or is re-tracing the mylar my only option? (I find it strange that ALL keys should be dead and not only some, as I encountered on failing XE keyboards. Can the Mitsumi keyboard be interchanged with other types? I do have a NOS Stackpole from B&C in storage somewhere. Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted October 10, 2017 Share Posted October 10, 2017 Swap out the 4000-series keyboard demuxers. One or both are probably dead. 1 Quote Link to comment Share on other sites More sharing options...
ACML Posted October 10, 2017 Share Posted October 10, 2017 Swap out the 4000-series keyboard demuxers. One or both are probably dead. Yes, do this, as I've had this same issue that was remedied by replacing the two demuxers (chips says 4051). And yes, Hi Tek and Stackpole 800 keyboards can be replaced, but keep the Mitsumi if you can, they are awesome. Even if you swap the 4051s, you may still find no response in the Mitsumi if the mylar contact traces are oxidized (very likely). The fix is the same for the 1200XL Mitsumi keyboards. Quote Link to comment Share on other sites More sharing options...
+slx Posted October 10, 2017 Author Share Posted October 10, 2017 Are the 4050s the Z103/4 that are mentioned in the field service manual? Quote Link to comment Share on other sites More sharing options...
ACML Posted October 10, 2017 Share Posted October 10, 2017 Are the 4050s the Z103/4 that are mentioned in the field service manual? The 4050 is the video signal. The 4051s are the keyboard decoders. Quote Link to comment Share on other sites More sharing options...
+slx Posted October 17, 2017 Author Share Posted October 17, 2017 Found the 4051s and replaced them (cheap fun at less than 1€ a piece ) but apparently that wasn't the fault. Only the "9" key is working (which I probably did not test before), everything else seems to be dead. So I think I'll have to repaint the mylar. Quote Link to comment Share on other sites More sharing options...
ACML Posted October 17, 2017 Share Posted October 17, 2017 Found the 4051s and replaced them (cheap fun at less than 1€ a piece ) but apparently that wasn't the fault. Only the "9" key is working (which I probably did not test before), everything else seems to be dead. So I think I'll have to repaint the mylar. Yes, this is classic Mitsumi behavior 35+ years later. Follow the Retrobits procedure for the 1200XL Mitsumi repair. The keyboard repair is the same. 1 Quote Link to comment Share on other sites More sharing options...
flashjazzcat Posted October 17, 2017 Share Posted October 17, 2017 2 Quote Link to comment Share on other sites More sharing options...
+slx Posted October 17, 2017 Author Share Posted October 17, 2017 Thanks, watched that already. Just need to dig out that silver paint from my hoarder style basement. Gesendet von iPhone mit Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
Rob Mitchell Posted October 29, 2022 Share Posted October 29, 2022 Old thread helped me .. I had a dead 800 keyboard fault .. I ruled out the POKEY, swapped with another working keyboard so ruled out that. Swapped in two 4051s and now fully working! Thanks! 2 Quote Link to comment Share on other sites More sharing options...
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