Mac Classic giving me an unexpected checkerboard.

[CC_333]

Hi,

My Classic II has similar symptoms, except it has solid vertical bars across the screen.

I tried recapping the analog board, and it didn't fix a thing-- I can get it to boot, however, if I disconnect the hard drive and floppy drive and let it warm up. The voltage slowly rises from about 4.2~4.35 volts until it chimes at about 4.6~4.75 volts, then it'll boot from an external, self-powered disk drive (a ZIP drive in this case), although the screen artifacts are still present, and things are very erratic and unstable. Have you tried disconnecting the drives? I saw that you did that before, but how about with the new analog board?

Good luck!

c

 

[Macdrone]

He said my board that I sent him was way worse voltage wise than the one he had, and had artifacts so I'm sure it won't do that at all at this point.

 

[krye]

@macdrone. It could have very well been damaged in shipping. The box was trashed when I got it.

 

[nvdeynde]

Measure your voltages directly on the PCB of the Analog board after recapping, the measurement at the external floppy drive connector isn't always reliable.

I see the picture is distorted: this is normal as you have to adjust brightness, contrast, V-size, H-size, V-centering, H-centering, focus on the Analog board.

Then probably the centering rings on the Yoke of the CRT. This is standard procedure after replacing the analog board.

However this will not solve your problem: if you tried a good recapped analog board where the voltages were within specs, your logic board is likely beyond repair. A short or wrongly positioned capacitor on the logic board can pull down the output voltage of the analog board.

Therefore it's best to measure voltages directly on the analog board with the logic board disconnected.

A simply test: disconnect the logic board and measure the +5 and +12 line at the HDD connector with a drive connected. What does this give ?

Forget fiddling with the voltage screw on the analog board: this is usefull for quick testing but not a solution.

After recapping the voltage of the analog board should be spot on. Don't waist your time with non-recapped analog boards as the capacitors used on the Classic I/II series are from very poor quality.

 

[Macdrone]

I am so sorry, when I get a paid again ill send that other board and you can just swap or pull off that plastic connector. Ill ups it.

 

[krye]

Cool. Thanks.

 

[uniserver]

have you poped the rom's out and poped them back in?

 

[krye]

Hum. No. I'll have to try that when I get home.

 

[tt]

I still suspect the logic board/ROM as well.

 

[krye]

No dice. Not the ROM. Same behavior after being reseated.

 

[uniserver]

look really close at your cap job,,, also look for solder bridges, little bits of solder can land and cause issues,

Might have to get real close with a bright light.

Also i think there are other caps on that board as well other then just 16v/47

i think its funny how you got it to work before the cap job… and after the cap job, no dice.

 

[nvdeynde]

As I wrote earlier, there's probably a short circuit on the logic board, probably near the replaced capacitors.

If not, then the logic board is beyond repair. Long term undervoltage can cause other components to fail.