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Mac Plus Horizontal Line and Speaker Noise Boot Issues


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Good afternoon all,

 

I have acquired two Mac Plus units of which neither want to boot.

 

I've started with the usual logic and analog board cleaning and recapping to no avail.

The most promising combination of boards only achieves a white horizontal line accompanied by noise from the speaker, as seen in this video:

 

Other combinations of board only achieve a flupping noise at various speeds with a blank screen.

 

Nothing seems particularly broken on any of the boards, except scorching underneath the 5W 1Kohm resistor on both of the analog boards, both of which tested open and have subsequently been replaced.

 

I know there are a lot of variables at work here and not having a working system to swap parts and narrow down the problems makes it more difficult to diagnose, but are there any specific areas that need checking/replacing to start off?

 

Thanks 

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According to Larry Pina's The Dead Mac Scrolls, which you can download here...

 http://maccaps.com/MacCaps/Repair_books_files/The%20Dead%20Mac%20Scrolls.pdf

(Thanks again Uni for preserving those books by the way, in case you're reading this! Which I doubt but still...)

 

 

... There could be multiple causes to your multiple problems (yep that sucks all right)

 

Pages 49 and 50 cover the display issue. Of course if that doesn't work, bad caps* could still be the culprit. 

 

About that sound issue: Again, multiple things could have gone wrong, I suggest trying first if the audio on the logic board is corrupted as well.

 

The Flup Flup Flup thing is most probably caps*, again. (see pages 24 through 27 of the book for a more detailed diagnosis).

 

 

* Someone on this forum listed the caps for the euro version of the analog board (220V, yes the caps are apparently slightly different) but I can't find the link to that thread right now. I need to recap mine as well, it has a similar issue: the line's vertical not horizontal in my case.

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Oh, here it is! Found it! From here

 

Macintosh Plus Analog Board (International version 230 volts)

- 4x 2200uf, 16v Radial: D=18mm, H=35mm
- 1x 4700uf, 16v Radial: D=18mm, H=35mm
- 1x1000uf, 16v Radial: D=16mm, H=25mm
- 1x 220uf, 16v Radial: D=10mm, H=20mm
- 2x 470uf, 10v Radial: D=8mm, H=12mm
- 2x 22uf, 50v Axial: L=16mm
- 1x 47uf, 16v Axial: L=14mm
- 1x 33uf, 16v Axial: L=13mm
- 2x 4700pF, 250v Box: L=13mm
- 1x 474K, 400V Metal Poly: L=23mm
- 1x 3.9uf 35v Bi Polar: D=18mm, H=35mm

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  • 3 weeks later...

I've finally got round to looking at these Pluses, and interestingly/unfortunately the analog boards are working fine as they boot up the logic board borrowed from a working plus just fine. 

 

Larry Pina suggests the 5v regulator or the TSM chip is to blame for logic board related flupping. I've tried replacing both of these with no success.

Are there any other "usual" suspects or is it a case of checking for bad traces? Swapping ROMs and RAMs doesn't seem to help either  xx(

 

Thanks 

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