Wanted to update this thread.
I was not able to find out if the mainboard RAM was part of one or both of the LSI chips. Fanuc understandably was not willing to put much effort into digging up information for a 30+ year old control. They did have tested exchange boards ready to ship if needed. Price of course is quite high and likely more than the true value of the machine.
Machine owner sourced a reasonably priced replacement main board from a machine being scrapped. I installed it and all is good again.
Do you have a photo of the "Junked board " ?
I could take a stab at that... Been going through the FANUG 10/100 series, FANUC 11 /11O series FANUC 12/120 series... (Very interesting to see how that has all evolved especially the transition from 11 series to 12 series.).
(Just for future reference ?).
Later on those LSI chips are more geared towards servo control (on main board and additional axis cards.).
In the sections on the FANUC 11 series documentation there are a couple of "cryptic" diagrams that seem to indicate there could indeed be a separate memory array (not integrated with LSI chips.).
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It is interesting that FANUC's approach is that if there's anything "squiffy " RAM or ROM or RAM/ROM (separate board) the manual advises "replace the whole board " kind of thing but I wonder if that's partially in the interest of safety/ product reliability but also
provides FANUC the "Opportunity" to supply an improved board ;-) ?
@Vancbiker ---> Just kinda interested in your thoughts on that … If there is a board that is prone to memory failures let's say over a ten year period does FANUC engineer better replacement boards … OR is it just the same board more or less and will probably fail in the same way again ?
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Roughly speaking how much would a replacement master PCB / board be 11 series (do you reckon) ?
Ta...