7 Feb
2015
7 Feb
'15
5:09 p.m.
On 2/7/2015 3:37 PM, Josh Dersch wrote:
On 2/7/2015 12:37 PM, tony duell wrote:
OK, I probed things out and there are two discoveries to report:
1. Continuity of KIN3 is good from the keyboard PCB to IC1 (the
SC7852) in 98. That's good!
2. KIN3 and KIN4 (KIN4 is used for "SHIFT") appear to be shorted
together somewhere. That's bad, but explains some of the bizarre
behavior...
I'll have to do a bit more poking around to see if I can figure out
where this is happening. The membrane is well attached to the PCB
after removing the boards from the housing, so I assume they're glued
and/or soldered together...
Thanks,
- Josh
Found a tiny solder bridge on the keyboard PCB just below where the
membrane is attached, between KIN3 and KIN4; I removed it and now
everything is working properly, except the SML key still puts the
machine into some manner of Japanese input mode rather than lowercase
(which doesn't really work well since this machine doesn't have the
Kanji character sets in ROM...). Not sure what the cause of that is,
but it's a pretty minor issue all things considered.
Thanks for the input here!
- Josh
I'm
more concerned about disconnecting the membrane from the PCB (the
PCB is on pg. 41/42, the membrane on 45/46 -- you can see on the lower
edge the connections made between the two) as I'm not sure how the two
are held together -- there's a metal bracket on top that sandwiches the
two together (and is screwed into the "front" of the machine -- see
parts 20/21 on the exploded disassembly). I'm afraid if I take the two
apart I may never get them back together making good contact again.
Have you dealt with anything like this? Anything I should be concerned
about?
I wouldn't separate them unless you have to, You may well find they
are
lightly glued or even soldered, if so, do not separate them at the start. Of course
if the membrane comes off when you undo the screws then it is intended that
it is separated during servicing, so no worries.
When you have the PCB out, then do a continuity check on the signal in question,
Even if you find it open, make sure the 'open' is at the junction of membrane
and
PCB, not an open track on one or other.
-tony