Black screen on Macintosh plus

[MattBranth]

Hello everyone!

I'm in the process of refurbishing a 1988 Mac plus. For the moment, when I turn it on, it's a black screen.

I took it apart, the analog board seems to be a problem. Indeed, a part of the board is corroded. Below are some pictures from different angles:











If you are familiar with these board, what can I do to improve things?

Another problem, the floppy drive seems to be damaged as well. Below are some pictures:







On this last picture, there is a floppy disk in the drive.

The read head seems to be partly detached, I don't know if this can be fixed easily.

Thanks in advance for your help!

Matthieu

 

[joshc]

Make sure the brightness is turned up.

Reflow the solder joints for the yoke connector and logic board power connector.

read voltages from the floppy port at the back of the machine with it switched on. What are the readings?

 

[bibilit]

A lot of broken joints in your board, common issue.

 

[MattBranth]

Make sure the brightness is turned up.

Reflow the solder joints for the yoke connector and logic board power connector.

read voltages from the floppy port at the back of the machine with it switched on. What are the readings?

View attachment 47817

Thank you for this answer, there is no tension in this floppy port when the machine is switched on.

 

[MattBranth]

A lot of broken joints in your board, common issue.

I redid all the soldering that you framed but unfortunately this does not change the result

 

[joshc]

Thank you for this answer, there is no tension in this floppy port when the machine is switched on.

What do you mean? Everything reading zero or?
Does the Mac make a beep when it turns on?

 

[MattBranth]

What do you mean? Everything reading zero or?
Does the Mac make a beep when it turns on?

Yes, everything reading zero (to measure the voltage I used a voltmeter to measure the voltage between the different holes, is that what was expected?)
And, no, the Mac don't make any beep when it turns on.

 

[MattBranth]

The fuse on the analog board is broken, this must be part of the problem...

 

[MattBranth]

I will try to replace the fuse, but in that case, maybe the big black rectangle component in the input is defective?

 

[joshc]

Fuses blow for a reason. You can replace it but finding the fault on your board should be done before powering up again, there is likely a faulty component/short somewhere on your board.

 

[bibilit]

Not your issue here, yes fuse is blowing for a reason.
Try looking for short components first.
Bridge rectifier…

 

[cheesestraws]

The big black rectangle is just some coils of wire. Very little to go wrong in that.

Check the diodes immediately across the mains.

Be very careful working on power supplies if you're not used to it, you can damage yourself very easily. Pretty sure one of the heatsinks on that board is live, so be extra careful.

 

[MattBranth]

How can I check the diodes, and others components? How to look for short?

 

[MattBranth]

Which components are the heatsinks? How to reconize them?

 

[MattBranth]

I ckeck all the diodes with my multimeter and they are all OK

 

[joshc]

I think you’d need to check them out of circuit, as testing in circuit can give inaccurate results I believe.

A component tester is a worthwhile purchase as it makes this easier.

The heat sinks on these boards are small pieces of metal attached to components to dissipate heat from them.

 

[joshc]

Be very careful working on power supplies if you're not used to it, you can damage yourself very easily. Pretty sure one of the heatsinks on that board is live, so be extra careful.

Second this. Best to avoid trying to do complex repair on an analog board/power supply if you are not confident - they can be dangerous.

 

[MattBranth]

I resoldered some parts and changed the fuse. Now the screen lights up!

But I have this error that appears. Any idea?

 

[joshc]

Try reseating the RAM

 

[MattBranth]

I changed the RAM chips having another mac available for parts.

New error now: 022000