I tried the dishwashing trick, but it did not help. The same
checkerboard pattern is there after washing in the sink, rinsing and
drying. What happened after drying is that white and brown deposits became
visible in the area of the RAM and upgrade sockets, both front and back
sides of logic board. I figure there are some shorts due to the deposits.
The person who performed the upgrade used the wrong type of solder!!
Here is what else I tried:
Put RAM in another computer. All 512KB RAM functions fine.
Pull all RAM out. Screen is blank.
Pull the upgrade card out. Upper quarter of checkerboard is
different. Some rows are only one pixel high.
Any insights?
Edwin
p.s. images of the board (500KB) available on request per private email.
At 07:08 PM 3/20/05 -0800, you wrote:
>You've tried most of the standard things. Here's one more to try: As
>bizarre and counterintuitive it sounds, washing the logic board may fix
>the problem. Some have used a dishwasher, others a good soak in some
>soapy water, and still others an alcohol bath. The electrolytics on
>those compacts tend to leak badly over time, leaving a conductive
>residue that wreaks havoc. Just rinse and dry thoroughly before powering up.
>
>> I found in the trash a fat Mac that gives a checkerboard pattern when
>>the power is applied. There is no startup tone audible. The pattern is
>>about 15 squares wide and 40 squares high. Any ideas on repairing the
>>problem (besides buying a Macintosh 128 logic board)? Here is what I have
>>tried so far, after Googling:
>> Pull the RAM and ROM chips and upgrade card (see below), and reseat
>>them (in correct orientation, of course). Same checkerboard.
>> Replace the 2 banks of 1256-15 chips with known good 1256-12 chips.
>>Same checkerboard.
>> Replace the 2 banks of 1256-15 chips with known good 1256-10 chips.
>>Vertical stripes.
>> Replace the 2 banks of 1256-15 chips with known good 164-12 chips.
>>Blank screen.
>> Quick power off, power on cycle. Same checkerboard, but a few pixels
>>reversed.
>
>--
>Prof. Thomas H. Lee
>Center for Integrated Systems, CIS-205
>420 Via Palou Mall
>Stanford University
>Stanford, CA 94305-4070
>http://www-smirc.stanford.edu
>650-725-3709 voice, -3383 fax
>
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