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warmech

Dead-ish Mac Classic II - Grey Screen with Thin Vertical Lines

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Hey everyone, I've been working on my Classic II and have hit a bit of a roadblock. I get a very, very quiet startup chime, but it only gives me the following display:

 

IMG_1802.thumb.jpg.451f2c98da705cd73308de43a171a8b6.jpg

 

I'm getting 5.00v even and 11.4v off the logic board connector, which seems in spec but may be too low. The thin lines have activity going on in the background, but it's impossible to tell what's happening. My board (below) is in good shape with no cap damage as far as I can tell:

 

IMG_1803.thumb.jpg.1336fe51817795dc62114575b6470cf7.jpg

 

I've dealt with checkerboard issues before, but this is brand spanking new to me. Would anyone have any thoughts about where to start looking?

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8 hours ago, cheesestraws said:

11.4 seems decidedly too low to me.  It really ought to be nearer 12.

Yeah, I was worried about that. I have a few 5v/12v switching power supplies for some of my arcade games that I could splice in and try. What exactly does the 12v drive on one of these boards?

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Have you replaced the capacitors on the logic board yet? If they have not been replaced yet, this is the first place to start troubleshooting. Even if the original capacitors don't look bad (at least without heavy magnification), they are almost guaranteed to be bad. They are likely one of the reasons this board is not working.

 

I think the Analog Boards on the Classic line are supposed to be temperamental, and it sounds like you may also have a power supply problem too. If there is not enough voltage going into the motherboard, there will be a checkerboard too.

 

This board definitely looks like it is in good shape, and I think it will clean up quite well!

Edited by davidg5678

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Recap the analog board!

Perhaps you have to change the optocoupler.

Sometimes the mosfet is defect and diodes can fail.

DP4, DP3, TDA4605, CNY17G-3

 

Edited by dochilli

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Alrighty - parts have been ordered: caps, diodes, and the opto IC for the analog board, and tantalum caps for the logic board. I assembled my Mouser cart as a project so anyone can order the same stuff in the future - https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=79cc59f895.

 

I wish they were still doing will call; I live a short drive away from them but, given the coronavirus, I completely understand not letting folks in the building, lol. I'll post back Wednesday evening once I have the parts. The analog board shouldn't take but a few minutes; wish me luck on the logic board, however...

Edited by warmech

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Alrighty, I've recapped this board and tried it in a few Classics to some avail. It was working for a while, but has now gone back to behaving as before. Anyone have any additional insight before I shelve this thing?

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Welp, it's officially fried. Oh well, it can at least serve as a scrap board for some other stuff. Guess I'm looking for a Classic II logic board now, lol.

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I think there is a chip on these boards labeled egret which can cause many problems if electrolyte gets underneath it. Before you shelve this board, I would recommend using hot air to remove the egret chip, cleaning the PCB really well with alcohol, and reinstalling the chip. This might help solve your problems.

 

Otherwise, if you are willing to sell your dead board, I may be interested in buying it. :)

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