27 Sep
2023
27 Sep
'23
1:39 p.m.
Hi Jonathan, thanks for your thoughs. I am still using
the same NVRAM, just with external battery attached, so no Chineese counterfeit.
My hypothesis is: With the battery losing voltage, some bits flip first. They cause the
error message you see and values get set to proper values. But there are some bytes which
must not flip because they determine e.g. the type of graphics, processor, speed, RAM
timing etc. If one of these bits flips first, than one is lost because the machine does
not reach the OpenBoot firmware because it tries to test non-existing hardware etc. etc.
I wouldn't think that's possible, the small portion of NVRAM used to set
parameters is checksummed, so it's unlikely a random combination would also result in
a correct checksum.
Still, to rule that out, try blanking the NVRAM by writing all zeroes to it. You may be
able to do that with something like a TL866+ and a shim socket -- don't just plug the
DS1553 right in, as it's got two output pins that may cause a conflict!
Thanks,
Jonathan