On Fri, Sep 20, 2013 at 10:16 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
On Fri, Sep 13, 2013 at 12:17 PM, Ethan Dicks
<ethan.dicks at gmail.com> wrote:
> Hi, All,
>
> A list member recently sent me a broken Mac128 logic board...
In anticipation of pulling and replacing 1/3 the DRAMs on this board,
I tried the trick of a dry-fit piggyback with known good chips on the
locations marked as bad. I can report 100% success. I stuck 6 new
chips on the 6 bad chips and got past the Sad Mac. In the light of
the several reports I found on support forums, all I can imagine is
that if these people replaced their bad RAM chips, either they misread
the conversion table and replaced the wrong chips, they damaged the
chips or the mainboard traces during the repair process, or they just
have a bunch of cold, dry solder joints.
Present state: machine gives "bong" when turning on (it always did),
usual screep wipe happens, then the "[?]" disk icon flashes. I have
one 400K drive, an OA-D34V-22, and (for now), Rev A ROMs. This
combination does not work. It tries to read disk, ejects it, then
asks for another one. I already have the -B ROM images and just need
to burn a pair of 27256s since that's an easier path than locating a
working, original revision OA-D34V drive mech. On the OA-D34V-22 I do
have, it did require removing petrified grease from the old eject
mechanism. I have some white lithium grease I'm contemplating using
unless there is some magic grease the job requires.
So the repair is nearly complete. Bad trace/repair damage
found/fixed, bad RAMs identified and tested, and a couple items to
complete to finish the job.
-ethan