Classic Rev. A Parts in an SE/30? - Macintosh Garden

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2011, May 1 - 2:54am

#1

bicostp

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Joined: 2009 Aug 17

Classic Rev. A Parts in an SE/30?

I've got an SE/30 that has been around for as long as I can remember, but over the past several years the screen has gradually become dimmer and dimmer. No amount of fiddling with the analog board pots solved the issue, so I'm looking at either replacing parts on the analog board or replacing the tube. I haven't been able to find any information about this particular issue online; all the relevant repair guides out there just say "adjust the pots" or "reseat the ROM board".

Someone at work threw away an early model Classic (October 1990), which will serve as a parts donor. The display works beautifully, but the logic board is irreparably damaged. The plan is to swap Superdrives and put the Classic CRT into the SE/30 and hope that solves the display issue.

There's no doubt in my mind that the floppy drive will swap over, but I'm not 100% sure about the CRT. From what I've read, early Classics used a lot of display components from earlier models, so I guess I lucked out there. I don't have the SE/30 inside right now, but judging from this teardown it uses the same yoke assembly with the same 4 pin connector. (The board on the end of the tube is hardwired to the analog board, but those just pop off.) Correct me if I'm wrong, but the Clinton display in the Classic should plug right into the SE/30's analog board, right? Just in case, was there any difference between the Clinton and Samsung displays which would prevent swapping between the two from working?

The only other thing I can think of is the flyback transformer itself is going bad, or parts on the analog board which supply it power are failing. Both are possible to fix, but more difficult to diagnose than just swapping tubes should be.

Any second opinions? I'd really like to get my SE/30 up to snuff again.

Thanks!

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2011, May 1 - 4:52am

#2

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Renegade

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Joined: 2009 May 17

Hi,

According to the 68kmla forum, a 1990 Classic should have a type A connector, just like the SE/30 (http://68kmla.org/forums/viewtopic.php?f=7&t=477).

Anyway, please consider saving both compact macs. Finding a working logic board for the Classic shouldn't be that hard, same for the SE(/30) analog board. "CRTs rarely fail" says Apple in the compact macs' service manuals

Cheers,

R.

2011, May 1 - 6:11am

#3

bicostp

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Joined: 2009 Aug 17

So it should just bolt right up?

The reason I suspect the CRT is I can't find any information about this issue (SE/30 specific pages are almost exclusively about the logic board), and aside from the dark picture it works perfectly. I'd have to do the floppy port multimeter test to confirm the low voltages, but they should be fine. It's either the tube or the high voltage portions of the analog board, so why not start with the easier part to replace?

The Classic is a parts mule, and the useful parts are going into refurbishing the SE/30. I've already got an 800k SE for doing 9" 8mhz stuff with, don't really need another one.

2011, May 1 - 1:12pm

#4

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MCP

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Joined: 2010 Mar 12

68kmla.net

2011, May 2 - 3:57am

#5

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MikeTomTom

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Joined: 2009 Dec 7

I don't know the answer to direct swapping a Classic's CRT into an SE/30 chassis, but http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html is a useful SE/30 repair page. Good luck with your project.

2011, May 9 - 1:40am

#6

bicostp

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Joined: 2009 Aug 17

Well I just finished swapping the parts, and my SE/30 works like new again! The yoke assembly plugged right into the analog board (in fact it's exactly the same part), no major adjustments required. The only thing I had to do was turn down the cutoff voltage, because it was maxed out in an attempt to squeeze more life out of the bad tube.

If your Mac's screen is getting progressively dimmer, both the brightness knob and adjustment pot are as high as they'll go, and the Mac itself works fine otherwise, you've probably got a bad CRT.