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Old 17 August 2009, 11:58   #1
MagerValp
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Leaking audio caps in A4000

I'm currently rescuing an A4000 from being eaten up by leaking caps and batteries. Replacing the battery with a fresh NiMH was simple enough, and there doesn't appear to be any damage to the board. The leaking audio caps are trickier though. I have posted some pictures here:

http://picasaweb.google.com/MagerValp/A4000

As you can see the 22 µF caps are surrounded by unhealthy looking brownish stuff, and the 74F08 at U710 has several cracked legs. Amazingly enough the machine still appears to work, and Anthony Hoffman's audio repair guide should be all I need to do the repairs. I just have a couple of questions that I'm hoping someone here can answer:

* What exactly does U710 do? I can't seem to find it in the A4000 schematics.

* What's the SMT packaging called for those 22 µF caps? I'm used to DIP sockets and oldschool caps, not this newfangled surface mount stuff :) It'd be super helpful if someone could locate them in the ELFA catalogue, as that's where I'll be buying the replacements.

Last edited by MagerValp; 18 August 2009 at 08:47. Reason: Fixed U170->U710
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Old 17 August 2009, 20:29   #2
rkauer
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The 74F08 is a quadruple AND gates. The "F" version is the fastest real TTL version.

If you can't find it as a "package", that's why they use just the AND ports on the schematics.

Here goes an schematic/datasheet of the piece.

http://www.google.com.br/url?sa=t&so...67wfEkFv_EDXPw
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Old 18 August 2009, 08:46   #3
MagerValp
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Right, I know what a 74F08 is, I'm just wondering what it's application is as U710. The mere fact that the computer appears to work just fine with the chip half fallen out has me puzzled :) Three of the four AND gates are shown as unused on sheet 14 of 16 ("Buster & expansion bus logic") in the schematics, and I can't see any other AND gates on that page.

Last edited by MagerValp; 18 August 2009 at 09:51.
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Old 18 August 2009, 15:39   #4
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I managed to find U710 in the schematics, it's on the video connector on the XCLK signal. I'm guessing that it's used for genlocks, something I couldn't care less about
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Old 18 August 2009, 15:44   #5
Chain
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yep, unless you dont need to sync amiga video from other machine/s you will not need it.
still, better to replace it sooner or later
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Old 18 August 2009, 22:16   #6
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Thanks for the confirmation. Me not replacing it also means me not toasting the motherboard, so I think I'll let the 74F08 be for now...
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