After capacitor replacement my Classic still doesn't work!

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Joined: Mar 23 2012
Posts: 5

Hello.

I have a Mac Classic that has recently stoped working. I'll start by describing what happened:

A received the Classic a few years ago and it has been working ok.

One thing that always caught my attention was that the startup bong has was very low (volume wise) and changing the volume had no real effect on the system. The volume was always low.

The last time it worked there was no startup bong the the computed booted OK (I wasn't wathing it boot, so I don't know if it took longer, or not, than usual).

The computer was used for cheking diskettes and copy some files for and from an external HD and it was left on for several hours.

After a while a noticed the the computer "hanged/crashed". I had a still image on screen but no response from the keyboard or mouse.

I tried to reboot the computed but I only got horizontal stripes.

I replaced the battery, cleaned the motherboard (with PCB cleaner) a replaced all of the following capacitors: C1, C2, C3, C4, C5, C6, C8 and C9.

I still only get perfect horizontal stripes.

What could be the problem now??

Thanks,
Paulo Melo

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speedyG's picture
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Joined: Nov 16 2011
Posts: 2407
Re: After capacitor replacement my Classic still doesn't work!

though i´m not that familiar with the mac - it sounds to me like a mistake in the horizontal sync.
this can have several different causes....

the first might be a damaged chip that is in the path for timing the video-signal... this could be proved with the aid of the cicuitplans of the related mac.... it might be usefull to proof if the related chips are seated well and pins are clean and and tight in their sockets...

the second could be the cable connection from the computer to the circuitboard that drives the display - it could be damaged or non-functional as result of a bad solderingpoint.... that could probably be solved by resoldering the points...

at the moment with this status and the fact that the computer did not issue a sound when finishing the booting-process it can´t even be determined if the boot completed, because you probably can´t identify a screwdup screen within the stripes...

it will be neccessary to first get the display running again befor you you can proceed to check the booting process...
a stupid question as result from the fact that i´m not familiar with the discussed mac...- does it have a connector for an external display ... - and if it is so... did you try to get a display by that connector - it would be one of my first steps to check that...?

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Joined: Mar 23 2012
Posts: 5
Re: After capacitor replacement my Classic still doesn't work!

Hello.

Thank you for your ideas.

The Macintosh Classic is a very old model (1990) and it doesn't have a connection for external display.

Regards,
Paulo Melo

speedyG's picture
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Joined: Nov 16 2011
Posts: 2407
Re: After capacitor replacement my Classic still doesn't work!

in the meanwhile i´ve did some research and found the follwing 2 links that might turn out to be valuable to you:
related papers:
http://members.optusnet.com.au/eviltim/macmp3/Mac_Classic_II.pdf
page 12, 22, 23 section "eagle-chip" and "videoboard" is related to the path of the problem
it shows at least the signals that should show up at an oscilliscope

one of the best manuals related to the topic with good pictures of the repair-sections is:
http://68kmla.org/files/classicmac2.pdf
it also contains a lot of drawn shematics of the video section that will probably be very needful....
and last not least it contain good descriptions of the repair-procedures...
good luck

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In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

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Joined: Mar 23 2012
Posts: 5
Re: After capacitor replacement my Classic still doesn't work!

Thank you for the link. I'll check them.