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Thread: Macintosh TV repaired


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Permlink Replies: 8 - Pages: 1 - Last Post: May 31, 2013 7:26 PM Last Post By: dougg3
dougg3

Posts: 190
Registered: 8/13/12
Macintosh TV repaired
Posted: May 4, 2013 7:53 PM
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So I recently bought a Macintosh TV on eBay, and I wanted to share my experience with it. Pictures are scattered throughout...



It was sold as working, but I guess there are different levels of what constitutes "working". It booted up fine, but the sound was extremely faint and the TV tuner didn't work. Yes, analog cable still exists and I have it. Anyway, I wasn't really upset about the condition of the computer. These machines are all ticking time bombs considering their use of electrolytic capacitors that tend to leak. It's just the way it is.

Since the audio amplifier circuit is on the analog board, I decided to replace all the capacitors on the analog board first:



As you can probably tell, it was absolutely filthy inside. I did a lot of cleaning while I had it open. The capacitors were no match for my Hakko 808 vacuum desoldering gun. I took many, many pictures and wrote down info about every capacitor beforehand so I'd have a good reference of where everything goes. I put the machine back together after replacing the caps and...there was no change in behavior. Next up, I decided to replace the capacitors on the logic board and the TV tuner board.





This got a little more tricky because I wasn't as careful as I should have been while desoldering the old surface mount electrolytics, and I destroyed a pad on the logic board in the process. I was able to fix it with some patch wire:



The rest of the recap was successful. Should I have used tantalums? Maybe, but I'm comfortable with the electrolytics for now. I can always replace them again, perhaps using a better technique than I used this time (Chip Quik?). After recapping the logic board, the sound was nice and loud again. Woohoo!

The TV tuner board has a very small Sony daughterboard on it (SBX1637A-01) that is covered with small electrolytics. It's just a failure waiting to happen, and indeed, the capacitors had leaked all over the place. I screwed up a few pads on the daughterboard, but luckily I didn't damage anything on the TV tuner board itself, which is a much rarer piece. After recapping the TV tuner board and leaving the Sony board off, the TV tuner worked again! No sound played from TV channels, though. Not a big deal though; the Sony board is an audio decoder, so that was expected.

I tried to repair the Sony board, and I thought I had succeeded, but apparently I didn't because the TV sound still didn't work after recapping it and repairing the broken pads. The SBX1637A-01 is a very common part used in TVs, so it was not a big deal to find a new one to use instead. In fact, I saw other people recommending to just replace the whole board instead of replacing the capacitors. I can see why, because they are packed pretty tightly together which makes them difficult to replace. Since the SBX1637 board is bound to fail due to the electrolytics, I decided to buy some 0.070" pitch headers on Digi-Key. This allowed me to socket it, so if it fails in the future it can be replaced without any soldering at all:



With the new SBX1637 board in place, the TV sound works perfectly now too! The only complaint I have left is that the hard drive, which appears to be the original hard drive, makes some very ugly sounds when you turn the system on or off. At some point I will have to find a solution to replace the hard drive. It's a type of Quantum hard drive that commonly goes bad, so I will definitely want to replace it sooner rather than later.



I got it fixed just in time to watch the Kentucky Derby. I was very happy to complete this fix before analog cable is completely phased out!

Here's a video of it in action: http://youtu.be/61k7yUXj6ck
landonf


Posts: 86
Registered: 7/23/12
Re: Macintosh TV repaired
Posted: May 4, 2013 8:16 PM   in response to: dougg3 in response to: dougg3
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dougg3 wrote:
The rest of the recap was successful. Should I have used tantalums? Maybe, but I'm comfortable with the electrolytics for now. I can always replace them again, perhaps using a better technique than I used this time (Chip Quik?). After recapping the logic board, the sound was nice and loud again. Woohoo!

Are there any downsides to tantalums vs. electrolytics? I've just been using tantalums when recapping out of the assumption that they'd live longer, but I'm not sure I have anything solid to prove that this is the case other that some forum posts I must have stumbled across.
dougg3

Posts: 190
Registered: 8/13/12
Re: Macintosh TV repaired
Posted: May 4, 2013 9:11 PM   in response to: landonf in response to: landonf
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My understanding is that yes, tantalums will live longer and they don't have the liquid inside that will eventually leak. I've also read that some people avoid tantalums because they can fail in pretty nasty ways when they do fail. But I've also seen a lot of people have success with tantalums in place of electrolytics in computers, so I don't really know...

There may be other subtle differences in behavior between the two (sounds like high current can be an issue with tantalums), and I don't know how much that behavior matters on a computer's logic board. With all the successes observed, I have no doubt that tantalums are a great idea to use when recapping. I guess I'm just comfortable using electrolytics because I'm replacing it with the same type of capacitor that Apple originally used. It does mean another recapping will probably be necessary in 20 years, but I'm cool with that :-)
landonf


Posts: 86
Registered: 7/23/12
Re: Macintosh TV repaired
Posted: May 4, 2013 9:33 PM   in response to: dougg3 in response to: dougg3
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dougg3 wrote:
There may be other subtle differences in behavior between the two (sounds like high current can be an issue with tantalums), and I don't know how much that behavior matters on a computer's logic board. With all the successes observed, I have no doubt that tantalums are a great idea to use when recapping. I guess I'm just comfortable using electrolytics because I'm replacing it with the same type of capacitor that Apple originally used. It does mean another recapping will probably be necessary in 20 years, but I'm cool with that :-)

Subtle differences in behavior are the main thing I'm worried about -- I imagine 20 years from now, when I'm floating in my nutrient tank and browsing the world-wide brain intermesh, keeping a 68k mac alive will seem outright primitive.
dougg3

Posts: 190
Registered: 8/13/12
Re: Macintosh TV repaired
Posted: May 5, 2013 10:48 AM   in response to: landonf in response to: landonf
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Hehe. I for one don't want to live in the Matrix!

As an example, I've found someone saying you shouldn't use tantalums with audio signals because they distort the sound. Not that it matters much; the speaker quality on this thing already sucks :) I just wonder if there's anything else that's technically out of spec about them when used in place of electrolytics. I doubt it's anything huge, but I don't know enough about capacitors to know for sure.
bbraun


Posts: 493
Registered: 7/25/12
Re: Macintosh TV repaired
Posted: May 5, 2013 11:16 AM   in response to: landonf in response to: landonf
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It is my understanding that there are behavioral differences that can affect AV signals, and that electrolytics are better for those. Take that with a grain of salt though, I'm repeating stuff I don't really understand.
I have had a tantalum fail and it exploded. Pop and pieces of it everywhere in the machine, the smell of magic smoke escaping, etc.

That said, I tend to use tantalums in everything I recap.
bbraun


Posts: 493
Registered: 7/25/12
Re: Macintosh TV repaired
Posted: May 5, 2013 11:50 AM   in response to: dougg3 in response to: dougg3
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Congrats on getting the Macintosh TV all repaired and working, that's pretty slick!
Along the lines of analog cable, I've got some old analog cable gear including a Q630 with the TV tuner, but no access to cable of any kind. I've been setting up a little cable TV system in the house. I picked up a couple agile modulators to convert svideo and composite video to an analog cable TV signal. I got a Channel Plus SVM-24 and two CableTronix CTARM-2LT pretty cheap off ebay. They recommend only using every other channel, so I'm using cable tv channels 17, 19, 21, 23, 25, 27, 29, and 31.

That's all great, but the real question is what content to feed those devices, and how to get modern content out to those analog signals. I keep a copy of my iTunes library reencoded at the handbrake "iPhone and iPod" setting (for the original iphone) for older devices that can't handle 1080p H264 content, like the original AppleTV, older iDevices, and my older OSX machines. Sharing this low-res iTunes library, I use an old tibook (which has builtin svideo out) to play a shared playlist on shuffle/repeat all, fullscreen. I'll probably also use a pismo (also builtin svideo), and old iDevices with the Apple composite out cable.

Anyway, it all generates analog TV channels from iTunes playlists.
Arbee

Posts: 61
Registered: 11/29/12
Re: Macintosh TV repaired
Posted: May 30, 2013 10:13 PM   in response to: bbraun in response to: bbraun
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Nice work on the Mac TV!

I also read vintage TV restoration forums, in part to remind myself that being into vintage computers isn't that weird ;-)

They always replace capacitors with like type of equal or higher voltage and temperature rating, and always Nichicon or Rubycon brand for electrolytics (those are the top quality / longest lasting). This is less critical for Macs where you'll never encounter a 600 volt B+ rail and the heat of 24+ tubes in a confined cabinet, of course.

Regarding broadcast, agile modulators are the way to go, as bbraun suggests, or if you have decent digital/HD reception a digital converter box will work too. Some US cities still have analog low-power broadcasts (e.g. channel 6 in Chicago which shows up a lot on YouTuber bandersentv's videos) but those probably won't last much longer.
dougg3

Posts: 190
Registered: 8/13/12
Re: Macintosh TV repaired
Posted: May 31, 2013 7:26 PM   in response to: Arbee in response to: Arbee
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Hehe, thanks!

Yeah, I used all Nichicon caps in my recap. I went on Digi-Key and filtered to get ones with a longer life and a higher temperature rating. It can be kind of hard to determine ESR ratings, but I also tried to go for low impedance or low ESR whenever I could, especially in the power supply caps.

Those agile modulators definitely look really nifty. One will definitely be bought once analog cable is no longer in existence here :)

I still need to fix the focus on the Mac TV...it is slightly blurry after the analog board recap. I don't remember it being that way before the recap...I see it should be pretty straightforward to adjust.

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