[sdiy] Prophet 5 Rev3 RAM issues

[Tom Wiltshire]

Have you got enough good RAM chips to get at least one of them going? You could always ask the owners to toss a coin…

The service manual suggests that the ~CS on the NVRAM needs to stay high until after the EPROM has powered up to avoid potential mayhem. PWR_DET does this, and holds the uP in reset too. If you had ~CS tied low, the NVRAM isn't protected. It need not be the timings, it might be power-up/power-down problems.

There *must* be something else you could put in there - 6514? 2114? I can't believe there aren't a few old RAMs still floating about somewhere. Have you tried asking people on the arcade game forums? Those things are stuffed full of these old chips...

HTH,
Tom


On 20 Sep 2015, at 22:17, John Henson <synthnerd at gmail.com> wrote:

> I have two Rev3.0 Prophet 5's here right now with bad 6508's in the battery backed up RAM, the availability of these chips is low and the costs very high, I built a piggyback board to use a 6116LP chip but while it mostly worked, the memory timings must not have been quite right as random bits got changed, I tied CS to ground and OE/ to the Chip enable from the original system, should I try this the other way around, and has anyone else out there had to do this?
> 
> John,
> www.retroactivesynth.com
> 
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