Re: Self-test IIC: Which RAM chip is bad?

[dempson@actrix.gen.nz (David Empson)]

stephen e buggie <buggie@ben14.unm.edu> wrote:

> Someone shipped me his IIc motherboard for repair.  First, I ENHANCED it
> with a BUGG-ROM --- Bugg-Rom adds the checkerboard self-test.
> 
> When I activated the self-test, this error message popped up:
> 
>         * RAM    ZP  0 1 0 0 0 0 0 0 0 
> 
> I know from the   *  asterisk that the bad RAM chip is in the upper bank
> --- the 8 RAM chips that are furthest back.   But which RAM specifically
> is bad???

The second one in from one end or the other.  I don't know which way
around these digits are supposed to be read (bit 7 on the left or bit 0
on the left), but assuming it is in the traditional order, then the
faulty RAM is the one containing bit 6.  According to my IIc technical
reference manual's circuit diagram, that would be chip UF5.

If the bits are being displayed in reverse order, then the faulty chip
is UF10 (bit 1 aux).

> Also, what does the "ZP" mean????

The fault was detected within Zero Page (the first 256 bytes of
auxiliary memory), preventing any further RAM from being tested.  There
is a possibility that there could be location-specific faults higher up
in memory which it hasn't been able to detect (yet).  You will have to
replace the faulty chip and run the test again to determine this.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand