Trying to rescue a Mac Plus

[Ildefonso]

Hello all you guys.

I'm having a lot of troubles trying to get an European Mac Plus to work.

When I start it I get the flup flup flup noice with a black screen.

After an other start try I get a series of start bongs with no image.

The third start try I get the starting bong and the image with the floppy disk, but the image is flickering, more in the sides then in the center of the image. But after a few minutes an other bong can be heard and the image of the floppy desapears substituted with black and white vertical lines.

I've detect a voltage drop in the 12V pin7 of the external floppy disk connector from the initial 12.80V down to 10.30V, when I only get black and white vertical stripes.

I've changed both CR20 and CR21, as so as the filter capacitors with no differente result in the sinthoms. Even tweeking the voltage regulator has no effect in the resulting voltage.

Any advice would be greatly appreciate because I'm making my best to safe the Plus from the trash.

 

[bibilit]

You should replace capacitors first (all C something units)

http://www.jagshouse.com/analog.html

The link above can be different as your own unit, but that is the idea.

Don't forget to remove old solder and refresh it on J1

 

[Ildefonso]

I've changed all the capacitors and refreshen all the solder joints in J1, J2 and J4.

The loose of voltage after a few minutes made me think in a capacitors problem but nothing has changed after recaping the analog board.

Could the variable resistor of the voltage regulator be part of the problem.

I ca'nt figure the responsible of the voltage loose...

 

[bibilit]

Don't remember clearly, but pretty sure there is an Optocoupler present in that board.

 

[bibilit]

The Optocoupler is U3  ref H11AX