Mac Classic giving me an unexpected checkerboard.

[nvdeynde]

The +5v and +12v are really way too low for a successfull boot.

These numbers show your Analog board needs recapping asap: the capacitors are definately degraded, probably most of them have already failed.

Try disconnecting the power of the HDD to reduce the load.

While it's not a solution in the long term you can increase the output voltage of your Analog board.

In the middle of the analog board ( component side ) there's a small white plastic screw. Turn it clockwise gently to increase the voltage.

However I strongly recommand this as a short term solution.

It's possible that adjusting the voltage pot isn't enough to get the voltage back in specs because too many capacitors are failing.

 

[krye]

Wow, you think it's the analog board too? I even pulled the analog board out and looked at it. There's no signs of any leaky caps.

 

[bibilit]

Yes, probably not getting enough V's to get it working, have you removed the Floppy and Hard Drive to test at a minimum load ?

 

[krye]

Yes, still does it.

 

[bibilit]

Have you a spare analog board for a test ??

 

[krye]

No. No spares.

 

[tt]

I'm not too familiar with the Classic board, but if the ROM is socketed, try reseating the chips or any other socketed chips.

 

[krye]

I guess I'll be on the lookout for a new analog board. I posted a WTB in the Trading Post.

 

[tt]

Did you try adjusting the voltage pot. on the analog board?

 

[8bitbubsy]

Replace the caps on the analog board as the guys in here are suggesting, it will do good. Don't rely on adjusting the voltage pot, the caps are getting worse and worse over time.

Replace with the same micro farad rating, and same voltage rating (or higher). Low ESR and 105 degrees celcius tolerance is recommended.

 

[tt]

Not suggesting kyre "rely" on adjusting a pot, but if the voltages can be temporarily placed at closer to nominal and the checkerboard is still happening, it may indicate the problem is with the logic board.

 

[krye]

I adjusted the pot until I got 12V and 5V and boom! It booted right up.



It did seem to take forever to boot off the System 7.5.3 floppy that I forgot was in the drive, but at least it works. Even the keyboard and mouse worked once it got to the Finder. I restarted it again and the screen went black. I shut it off and then attempted to try it again with a System 6.0.8 disk to see if that booted faster. I don't know if the painfully slow boot has something to do with the machine or if that's just how slow System 7.5.3 is.

In any case, the second attempt just gave me another checkerboard again. But I guess this proves that the logicboard is good and it is indeed a failing analog board?

 

[Macdrone]

Not really. Caps heat up on board parts a they are the same age and cascade failure. My classic boots but no chime, I have 3 analog boards and 5 motherboards, only one motherboard boots.

Just have both recapped, one test then recap the other. That way you will know if one helps more than the other.

Cross your fingers as if I do we'll recapping mine ill flood the boards with classic motherboards lol, all with full ram cards.

 

[nvdeynde]

Did you crack up the voltage as I suggested ? Gently turn the screw clockwise while you are measuring the +5 Volts line.

If you are unable to get +5V and +12V volts then you need to recap the Analog board first.

 

[krye]

Yes, read two posts up for results.

 

[8bitbubsy]

Yes, please do recap both the analog and digital board. And by that I mean *all* the electrolytic caps. If you don't have the caps you need, get them.

And yes, System 7.5.x on a floppy boots extremely slow on a Classic (I've tried it before).

 

[trag]

I have a Plus which used to start-up to the checkerboard and if I left it alone for about five minutes or so, it would suddenly chime and boot properly. So heating up can definitely have an effect.

 

[krye]

Yeah, I saw that trick in another thread. This doesn't fix itself once it's been on for a while.

 

[krye]

Here's an update.

Macdrone sent me a new analog board. He tested it in his machine and it boots. Unfortunately, it doesn't work in mine. It's actually worse.



I was able to eliminate the horizontal lines by adjusting the brightness knob, but the display is seriously warped and there's a lot of scattered noisy pixels. The warping moves down the display.





I tried adjusting the pot on the board to 12 and 5V, but it won't go that high. It maxes out at a little over 11 and 4 volts.

I'm already in the hole $30 for the caps and the board. I think I'll chalk this one up as a loss since I think it's a combination of the two boards not working. At this point, it might be easier (cheaper) to just keep my eye out for a new machine all together. Maybe finally get a Classic II or an SE/30.

 

[Macdrone]

Seriously the board didn't work? I did try it out, maybe the shipping did it in.

Good luck on finding a replacement Mac, I am truly sorry it didn't get the job done.