Color Classic No Boot

[appleg33k85]

Good Evening

Recently I acquired a Color Classic. When attempting to start it it powers on momentarily and then immediately off with the logic board in. With the logic board removed it continually power cycles which lead me to believe its an issue with the analog board. I've done a full recap on the analog board and still have the same symptoms. I'm not sure how to tell if the fuse is blown as its simply a white one that feels almost paperish. I'm open to trying to find a new fuse if thats the issue otherwise if someone could point me in the right direction it would be greatly appreciated.

 

[Elemenoh]

Maybe focus on the feedback circuit of the analog board. Consider changing the optocoupler and/or the diodes near it.

 

[appleg33k85]

I've gone ahead and replaced the optocoupler and TDA IC chips with no success. I also checked the major resistors and they all come up with the correct values. I went through the board and reflowed the solder joints to make sure that there are no cracks. The only thing that I see is the attached photo that is cracked but i'm not sure what the component is or what it does.

 

[rikerjoe]

That is a RIFA cap between the two transformers. I imagine you found the fuse by now, located near the mains voltage input. About a year ago I tried working on a problematic Color Classic analog board that started blowing fuses, telling me I have a short somewhere. I removed numerous parts and tested them out of circuit but never managed to find the faulty part or parts. I managed to get my hands on a cheap replacement analog board and moved on for now. Good luck in your repair, I’ll keep following along and will chime in from my limited although unsuccessful experience with the Color Classic analog board.

 

[appleg33k85]

An Update to this: I've replaced a few more common failure components. I replaced the RIFA cap that was cracked in the above photo along with a film cap. I also replaced the 1N4148 diodes and an IRFBC40 MOSFET. Board is still having the same issue and I feel like I'm coming up short on ideas of what the issue could be.

 

[Drake]

Good Evening

Recently I acquired a Color Classic. When attempting to start it it powers on momentarily and then immediately off with the logic board in. With the logic board removed it continually power cycles which lead me to believe its an issue with the analog board. I've done a full recap on the analog board and still have the same symptoms. I'm not sure how to tell if the fuse is blown as its simply a white one that feels almost paperish. I'm open to trying to find a new fuse if thats the issue otherwise if someone could point me in the right direction it would be greatly appreciated.

Can I see a photo of the logic board please, try and focus on some of the cap rework

 

[appleg33k85]

Can I see a photo of the logic board please, try and focus on some of the cap rework

Here are the best shots that I could get.

 

[appleg33k85]

Does it chime or does it not stay on long enough for that? It sounds like it might be an issue in the feedback circuit. It could be the optoisolator (see photo below) IC or surrounding resistors and diodes.

No, it does not chime, if the logic board isn't installed and the computer is turned on it sits and clicks. If the logic board is installed it will fast cycle (power light comes on and immediately goes off) if the soft power button is pressed. The optoisolator has been replaced, board is fully recapped, 1N4148 diodes have been replaced.

 

[Elemenoh]

No, it does not chime, if the logic board isn't installed and the computer is turned on it sits and clicks. If the logic board is installed it will fast cycle (power light comes on and immediately goes off) if the soft power button is pressed. The optoisolator has been replaced, board is fully recapped, 1N4148 diodes have been replaced.

Sorry just realized I gave you that same advice earlier.

No, it does not chime, if the logic board isn't installed and the computer is turned on it sits and clicks.

Normal operation is that the fan will run if the MLB is not installed. Did you recap and clean the logic board too? If you just get a brief click when it's installed you might have an issue with the EGRET chip which manages ADB. You might need to remove and clean underneath that chip if there's a lot of cap goo around it.

 

[appleg33k85]

Sorry just realized I gave you that same advice earlier.


Normal operation is that the fan will run if the MLB is not installed. Did you recap and clean the logic board too? If you just get a brief click when it's installed you might have an issue with the EGRET chip which manages ADB. You might need to remove and clean underneath that chip if there's a lot of cap goo around it.

I have not done anything with the logic board yet as the analog board issues need to be corrected first since it appears to be shorting when powered on (the consistent clicking when turned on without the logic board). If the rear case is on then the fan will turn on and off with the same frequency of the clicking sound.

 

[Drake]

I have not done anything with the logic board yet as the analog board issues need to be corrected first since it appears to be shorting when powered on (the consistent clicking when turned on without the logic board). If the rear case is on then the fan will turn on and off with the same frequency of the clicking sound.

I can honestly say that nothing jumps out at me, I was thinking about this since your message today and I remembered the TDA4605 chip. BUT I see in your above comment that you had replaced this already? I know I've had issues with it in the past. I see some small bodges, are these working as expected?
The symptom of power cycling though is strange behavior, I wish someone local to you had another board to cross check.