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#1 2016-12-27 07:18:32

frost.byte
Member
Registered: 2016-12-27
Posts: 4

Classic II Logic Board Cap/Resistor ID.

Hello all! I'm new to the forums, so I apologize if my formatting isn't up to snuff wink

I've had a Mac Classic II for about five years now, and long ago, I used the infamous 'washing machine' method of removing bad cap residue, in an attempt to remove the checkerboard pattern on boot.
In removing the checkerboard, I ended up with a new set of graphical glitches I could only describe with: Black bars filling slowly with white. I was dumbfounded. So, I set it aside, back in my closet.
Two years after, I pull it back out, determined to finally regain functionality in my Mac.

I do a close visual inspection of the logic board, and I notice a few SMD components missing on the underside. These are: R63, C86, and C96.
I figure my washing machine might've knocked these off in the numerous washes I gave the board years ago.
Having spent all day troubleshooting, in my frustration, I threw all caution to the wind, and I went and bridged 2/3 of the missing components with thin strands of copper wire.
Lo and behold, IT WORKED! The system boots up, (although not having any audio whatsoever, and a dead PRAM battery...) it works flawlessly!

I've ordered a set of new caps from DigiKey for the topside, but I figured i'd replace the missing components on the bottom while i'm at it. I simply lack the schematics for the board, and need the values of the components listed.

IMAG0529.jpg

IMAG0510.jpg

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#2 2016-12-27 11:15:50

max1zzz
Member
Registered: 2014-05-18
Posts: 207
Website

Re: Classic II Logic Board Cap/Resistor ID.

All the resistors around the missing ones are marked "220" or 22 Ohms, So it's reasonable to assume the missing ones are probably 22 ohm as well

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#3 2016-12-27 19:28:50

frost.byte
Member
Registered: 2016-12-27
Posts: 4

Re: Classic II Logic Board Cap/Resistor ID.

That seems like it might be the case, except there's a missing capacitor and I feel as though that might be contributing to my missing audio. (Either that, or I need to recap the analog board too.)

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#4 2016-12-28 01:39:18

max1zzz
Member
Registered: 2014-05-18
Posts: 207
Website

Re: Classic II Logic Board Cap/Resistor ID.

those caps will most likely just be filtering caps, which should be 100nf (the board should work fine without them)

The lack of sound is most likely as you haven't replaced the 'lytics on the board yet, once you have replaced those you will probably have working audio again smile

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#5 2016-12-28 05:11:10

macdrone
Member
From: Rainier, Or
Registered: 2014-05-25
Posts: 237

Re: Classic II Logic Board Cap/Resistor ID.

sound can be a grounded/bad speaker along with needing new caps.  Maccaps showed us that a couple of years ago.

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#6 2016-12-30 03:48:20

frost.byte
Member
Registered: 2016-12-27
Posts: 4

Re: Classic II Logic Board Cap/Resistor ID.

Well, it's finished. Not my finest work, given I lifted a pad, but not terrible for my first try at SMD soldering.

It WAS an adventure, that's for sure, and I learned a lot about how NOT to do certain things.

Lifted a pad to a cap, so I had to trace it to a pin of the audio amplifier.

The capacitor can be seen chillin' in a ball of tape between two ports.

IMAG0569.jpg

IMAG0563_Copy.jpg

At least my Mac can go "quack" now.

Last edited by frost.byte (2016-12-30 03:49:44)

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#7 2016-12-30 06:22:27

frost.byte
Member
Registered: 2016-12-27
Posts: 4

Re: Classic II Logic Board Cap/Resistor ID.

Just recapped the entire analog board. Stuck with a bright horizontal line ~ Checking all the solder joints now sad

Edit: Just found it : I made the embarrassing mistake of installing a capacitor backwards ( 25v 470uf )  Was easy to find, bottom puffed out.

I'm hoping I didn't fry the little TEA 2037A 99118 Horiz./Vert. Deflection IC too sad

Edit #2 - Yeah, definitely fried the IC. - Took a continuity test of the chip, and one of the Ground pins seemed to be completely disconnected. I suppose I could pick up any ol' 2037A from eBay?

Last edited by frost.byte (2016-12-30 08:45:36)

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