Macintosh Classic horizontal lines not booting

Question

ljmcochen Author

Level 1

8 points

Macintosh Classic horizontal lines not booting

Hi,

Recently, I put my hand on a Macintosh Classic.

When I turned it on the screen slowly came to life only to show horizontal lines :

The outside was stained by brown electronic juice (if I may call it that way), so I looked inside.

There I found the PRAM battery and the capacitors had leaked. Because the computer was stored on the side, most of the logic board remained untouched, by the battery leak, and the capacitors had cause more or less damage to their surroundings.

So, after consulting various forums and speaking to most of the IT people I know, few things were clear.

I cleaned the board entirely, using water, ethanol and finally acetone, and replaced the capacitors.

Here is the board now :

Damages near where the PRAM battery was installed, new capacitors and I had to resolver the small metallic Y1 (resistance I guess...)

Damages on the top left corner from the PRAM battery leak :

New capacitors, damages from the old ones (soldering on top is really hard, feel free to criticise 🙂 ) :

After I finished these repairs, I hoped the computer would work, but no, still horizontal lines, no sound whatsoever and after a few seconds, appeared a new pattern on the screen :

I have now spent my afternoon checking every possible trace on the PCB and they all seem to be fine...

Is there anything I can do to save that piece of Apple history ? 😀

null-OTHER, Mac OS 8.6 or Earlier, Mac Classic (1991)

Posted on Apr 10, 2017 10:04 AM

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Answer 1

Oct 28, 2017 5:57 PM in response to ljmcochen

Have you gotten yours to work? I have the same exact problem and was wondering if you have a working solution

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Answer 2

Jan Hedlund

Level 7

22,207 points

Apr 20, 2017 3:41 PM in response to ljmcochen

The Y1 component appears to be a crystal.

Given the amount of corrosion on this board, eliminating every possible fault will be extremely difficult. It may not be a bad idea to ask for further guidance at a site (such as 68kmla.org) where people discuss computer hardware repair specifically.

I assume that you are aware of the risks involved in connection with repair work inside a compact Macintosh computer. Such work is dangerous because of the high voltages, and must be performed by qualified personnel only. High-voltage charges can remain in the CRT and capacitors for a long time after the computer has been turned off and disconnected from the mains. The CRT is fragile.

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Answer 3

Drew Reece

Level 6

10,660 points

Apr 20, 2017 7:05 PM in response to ljmcochen

In the second image - IMG_3109.JPG

Look at the top edge of the board - do the pink & green traces slot into any connectors? That won't be a good connection judging by the colour of those traces (I don't know if they are just test traces or actually used in the case).

D1 looks like the trace leading to the through hole is possibly missing? Use a multimeter to check for continuity across that trace if you didn't already do that.

I suspect if you search you may find schematics if you are so inclined. It could help you work out which parts to look at for each issue, however if you are serious you should look for other help as testing many of the components requires oscilloscopes & other complex hardware. You would need more than an iron to lift & resolder many of those components.

Other forums may have info on finding reclaimed parts but you also have to evaluate the state of the HD & any other disks you have etc. You may be limited to what can be done if you don't have functioning floppies etc. I agree with Jan Hedlund too, Y1 looks like a timing crystal.

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Answer 4

ljmcochen Author

Level 1

8 points

Apr 26, 2017 4:38 AM in response to Jan Hedlund

Thank you, I'll have a look at 68kmla !

I confirm, Y1 is a crystal.

Then, I discharged everything that could be discharged every time I was going to put my hand in the hardware, and I moved everything very carefully, to avoid both breaking them and shocking myself in case any of them were still charged. Nothing bad happened on that side.

I also discovered that removing the ram caused the checkerboard to appear on startup...

I won't be able to do anything with the computer as I am back to uni for now, but I'll update when I go back home in July.

Thank you again !

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Answer 5

ljmcochen Author

Level 1

8 points

Apr 26, 2017 4:49 AM in response to Drew Reece

The top traces slot don't go the any connector, I guess they were used for testing by Apple.

The trace the D1 is completely dead, I removed the oxide to stop it from eating more of the trace. From what I've found, the through hole was just used to anchor firmly the PRAM battery holder bur was only going from the battery to D1, so I have soldered a wire to replace it. I have tested as many traces as one can test, the few traces that were dead (mainly going to the RTC) were replaced by thin wires (I don't have pictures with me).

I have both functioning floppies and a Performa 475 running 7.1 that is also compatible with the Classic if I remember well. I will test the Classic's HD using the Performa when I go back home.

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