Color Classic Logic Board faults

[glay78]

Hi I got 2 recapped boards here with 2 different problem 

Board 1

- powers up without chime and video

- no activity just a blank screen

Board 2

- does not power up on keyboard Power key

- only powers up when board is slid in with power switch ok

what could be the problems for the 2 boards as above? They have been recapped, washed and checked. Doesn’t looks like a cap problem but could be other traces or shorted component?

 

[bibilit]

Egret chip probably. 

 

[glay78]

Egret chip probably. 

Which is the chip and for which board?

 

[bibilit]

Probably both. 

The Egret chip is the one that is on the right side of the battery. 

U7

https://inanis.net/macintosh-color-classic/

 

[glay78]

Probably both. 

The Egret chip is the one that is on the right side of the battery. 

U27

https://inanis.net/macintosh-color-classic/

Is there a fix? 
 

 

[bibilit]

Removing the chip, cleaning pads and soldering back works most of the times. 

This chip is nearby a capacitor, goo goes underside. 

 

[glay78]

Removing the chip, cleaning pads and soldering back works most of the times. 

This chip is nearby a capacitor, goo goes underside. 

Alright thanks I’ll give it a try

 

[IlikeTech]

If you can't easily remove it I found scrubbing around it with 99 percent alcohol and a toothbrush to fix mine, but YMMV.

 

[glay78]

If you can't easily remove it I found scrubbing around it with 99 percent alcohol and a toothbrush to fix mine, but YMMV.

I’m gonna try that tomorrow. 
 

what about board 1 with no chime and no display?

 

[IlikeTech]

Did you clean the board after decapping?  I normally clean the pads and all around where the capacitors go after I've removed the old ones and before I put the new ones on.  It helps remove anything that might be an issue.  Some photos would be good.

 

[glay78]

Yea did clean it with alcohol and wipe. Only did major cleaning after recapping doesn’t works. 
 

 

[IlikeTech]

So it powers up with the KBD, just with no chime or display?

 

[glay78]

So it powers up with the KBD, just with no chime or display?

Yes before and after recapped it’s the same.

 

[IlikeTech]

Huh, strange.  Could you take some High Res photos and attach them?

 

[glay78]

Huh, strange.  Could you take some High Res photos and attach them?

Ok I’ll get it up tomorrow 

 

[IlikeTech]

Thanks!

 

[glay78]

Thanks to you guys too !

 

[bibilit]

what about board 1 with no chime and no display?

The Egret chip is a pretty clever unit, integrating an on-chip oscillator, reset, power saving and self test functions.

So chances are this is part of your issue, i have seen too many boards not working before and working after a simple remove and refit of this Egret.

So far, only have replaced one (removed from a Maxell Bomb destroyed board) so chances are pretty high to get your boards working again.

cleaning only never worked for me, fluid goo is conductive and can short several legs... even cut traces.

Hot air is the best option here.

Another possibility of failure is the Cristal oscillator Y2 next to it, was documented a couple of years ago.







Last but not least, another chip can go wrong, the other one next to the Egret, U8 (see pictures on the post above, where both have been removed)

I do both when i have an issue, for the sake of mind.

 

[glay78]

I did saw Techknight’s post and I’ve checked the continuity of the traces and they were good. So I’ll go with U7 first. Hope it works!