Posted By
MMS
on 2020-02-22
07:00:35
 |  Re: Problems loading Alpharay
Maybe off, maybe will be helpful
When I worked at a factory produced DVD players and LCD TVs (in fact some millions per year) such kind of random loads/hangups were typically due to RAM chip cold soldering on one of the legs (there were some PCB "craccked vias" and "delaminated/black pad BGA soldering" too, but in case of Plus/4 there are not so many, maybe zero).
We usually never see this sympthom with the sets running in the 500h long test hot chamber (preheated to 40°C), but typically on production lines at the longer EOL test. The deferct rate went up especially when the PCBs brough from the outer warehouse in wintertime.
(I spent some months analysing these random patterns due to a green belt quality improvement project made together with production team).
Most of these PCBs were returned (mixed back into the fresh good ones, after removing our defect sticker) by the PCB supplier due to "no fault found" at their side, as sometimes it required 2-5 minutes to reproduce the problem, and they never tested them so long, or just tested in a PCB jig, tested only 60-70% of ll functions (or the defect was so random, or the jig pressed the PCB in a was that the contact was OK in Jig, but Not OK in the finished product).
After my colleague idea to put a UV dot on the PCB edge, then it became evident, that out of those failing "fresh PCB", up to 30-40% were in fact alraedy returned by the PCB supplier 2-5 times (to these PCBs circulating between the two factories, rejected at out tests again and again ("defective"), and passing the supplier test again and again ("OK")!)
Only after doing a very detailed research on the boards with microscope, we found those almost not visible cold soldering on those RAM IC legs (or the sockets).
While these 200ns RAM chips are less sensitive to than those 80ns on DVDs (I mean the timings are expecting less proper timings), I suggest to check very thoroughly the soldering of the RAM chip socket, as I saw you swapped the RAM chips without success. So one explanation, that not the IC itself defective, but the socket.
The V4 may load better, if some timing could be less strict, so it may put less stress on the components. Also it gives an explanation, why the older games run fine on the machine, and the new continuoulsy "decompressing" and "trackloader" games are hanging up, due to strict timing on the stuff.
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