Posted by Chris
on 5/29/2008, 6:50 am, in reply to "question?"
66.191.27.16
To you and all the other JX-305 owners who have been following this issue:
I currently have a JX-305 with the infamous streak of half-lit pixels across the top of the LCD, and a steady beat-lite (the only signs of life). I bought it that way. I can't even get into any of the 11 factory diagnostics modes - no menus work.
The bright side is I bought it from someone who bought it new and used it for years before it failed.
From what I have been able to learn, one of the Flash RAM IC's (either U1, program flash or U7, user flash) has failed. U7 in my synth appears to have been replaced once (hmmm). The part in question is a Sharp LH28F800SUT-70 56-Pin TSOP Flash Ram IC (used in each location), which has .85mm pin spacing, so soldering requires a fine pitch ESD-safe soldering station, fine-pitch solder, wick, flux, and some skill to remove & replace.
Looking at the service manual schematics for the main board, I have not been able to identify any obvious design issues that would cause this part to die prematurely. Maybe the manufacturer obtained a bad lot of memory IC's, or cheap knock-off's that weren't made by Sharp (commonly caused by outsourcing PCB assembly to LCR (low cost region) vendors. Speculation...
I will post again once I have replaced at least one of these IC's and brought mine back to life.
The parts aren't available through the normal vendors, since they are old and non-RoHS (they contain lead).
Cheers,
Chris
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