The 230 had a passive matrix screen, did it not? In which case, an old passive matrix is prone to go bad with lots of ghosting, etc. They ghosted when they were new, after all.
Your best bet at this stage may be to take it (the lcd) off the machine in order to take it apart and put it back together again, unplugging every ribbon, etc., and then again reassembling so as to ensure good contacts again at all the connections.

If this doesn't work, more substantial problems await your care and attention. I seem to recall that macassemble (ebay store) has some new service parts for duos at the moment. You might take a peek there, but they are not a particularly cheap supplier.

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