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Macintosh Color Classic unable to boot after recap (AB & LB)


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I recently recapped the AB (Analog Board) & LB (logic Board) of a Macintosh Color Classic (CC).

The board is visually in good condition, lucky that the battery did not leak.

 

All the photographs are in the quote below, click to zoom the photograph.

 

The recap guide based on Bruce:

LB: https://recapamac.com.au/macintosh-colour-classic/

AB: https://recapamac.com.au/macintosh-cc-analog/

 

The AB was partially recapped as of recommendation from Bruce. Only that I did not replace the two of 5600uf 10V capacitors due to unavailability in my local market.

However, I did recap all the caps from the AB. On C2 & C3, I used smaller tantalum capacitor than the Bruce's guide which I believe has the same value(100uf 6.3V - 107J).

 

Symptoms before recapping:

- Boot success probability is 2 out of 10 attempts

- Distorted screen

- Purple screen

- No boot sound

 

Symptoms after recapping:

- No boot success at all

- Only shows retrace line

- Very hot 343S0129 chip

- No boot sounds before and after recap (the speaker might not functioning since it have some holes)

 

Other attempt:

- Clean and brushed the LB with soap + distilled water

- Soaked and let dry the LB with IPA

- Cleaned some of the gunks with plastic toothpick with extra care

 

Questions (each question doesn't have to be answered - only the thing that you may know):

1. Is 343S0129 chip is a sound chip?

2. Does smaller size capacitor with same value will affect the performance or function?

3. I experienced a retrace line problem with my Macintosh Classic before, the 2N3904 transistor on the video board was the issue. Is there any transistor equivalent to 2N3904 in CC video board?

4. Will bypassing a via from the guide in here help the problem? 

 

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This is the photograph that the CC is running before recapping, it has booted successfully in the probability 2 out of 10.

 

IMG_9805 copy.jpg


 

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And this is the photograph after recapping. It shows retrace line even after powering on and off many times (more than 10 times).

 

IMG_9952 copy.jpg

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Overview of the LB condition after recapping

 

IMG_9956.JPG

 

IMG_9961.JPG


 

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Overview of the AB condition after recapping

 

IMG_9902 copy.jpg

 

IMG_9866.JPG


 

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This is the 343S0129 chip that gets very hot

 

IMG_9953 copy.jpg


 

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C2 & C3 tantalum capacitor smaller in size with the same value

 

IMG_9957 copy.jpg

 

Edited by fatlobster
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1. Is 343S0129 chip is a sound chip? Yes it is and also part of the boot process

2. Does smaller size capacitor with same value will affect the performance or function? no, capacitors can be found in several sizes

 

I will have a look at the Egret chip (also named Cuda in the post above) doesn't look clean enough and responsible for a lot of boot issues in this board.

 

I don't see Rom chips in the picture, i imagine have been removed for cleaning purposes but back before any test ?

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On 4/7/2021 at 8:16 PM, bibilit said:

1. Is 343S0129 chip is a sound chip? Yes it is and also part of the boot process

2. Does smaller size capacitor with same value will affect the performance or function? no, capacitors can be found in several sizes

 

I will have a look at the Egret chip (also named Cuda in the post above) doesn't look clean enough and responsible for a lot of boot issues in this board.

 

I don't see Rom chips in the picture, i imagine have been removed for cleaning purposes but back before any test ?

 

Thank you bibilit for your explanations, I think it make sense that capacitors can be found in different sizes with same value.

 

I'm assuming that the Egret chip is indicated as U7, isn't it? I'll try to clean it thoroughly with IPA.

For the ROM chips, yes I took it off for cleaning purposes. I took picture before removal to make sure the correct position.

 

I've discovered that uniserver had this hot sound chip issue back in 2014, but the thread does not seem to be resolved.

 

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Otherwise,  Sometimes the board will power up but you will only get a grey screen, nothing else will happen, no tone, no boot.
and if you feel around the SOUND chip gets almost NUCLEAR hot.

 

http://thinkclassic.org/viewtopic.php?id=124

 

 

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19 hours ago, fatlobster said:

I'm assuming that the Egret chip is indicated as U7, isn't it? I'll try to clean it thoroughly with IPA.

 

yes it is, cleaning can help but removing and soldering back is so far the best solution (hard to clean under the chip itself)

 

U8 is also part of the boot process, so using the same method worked for me several times.

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Posted (edited)
On 4/8/2021 at 1:34 AM, bibilit said:

 

yes it is, cleaning can help but removing and soldering back is so far the best solution (hard to clean under the chip itself)

 

U8 is also part of the boot process, so using the same method worked for me several times.

 

Yesterday I manage to remove and solder back the U7 and U8 chips, when I tried to power on it doesn't boot at all. Today I tried to power it again with success, with the similar probability of success boot before recapping. It's easier to boot if I cold boot the system not so long after I shut it down. I noticed that the sound chip still get hot even if it has succeeded to boot. And I've also seen a pattern when the system successfully boot (the screen will appear jagged).

 

Things I suspect:

1) It has something to do with the bad caps on the AB. But I'm not sure which cap that might goes bad.

2) Sound chip needs replacement - I'm wondering if the sound chip from Macintosh LCII compatible to CC? (if it's the same, I'm planning to replace with it)

 

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Grey screen with retrace line indicate the system failed to boot

 

IMG_0098.JPG

 

 

 

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Jagged screen without retrace line indicate the system succeeded to boot

 

IMG_0107.JPG

 

 

Edited by fatlobster
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Probably an issue with the AB. 

 

My own is distorted a bit, but yours is far worse, probably not getting right voltages at some point. 

 

Yes IIRC, sound chip is identical.

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