Macintosh TV Recap Issue

[just.in.time]

Hi Everyone,

Attempting my first recap job.

After cleaning and recapping, I start up the computer (with the back access door removed).  Loud chimes, happy mac, 7.5.5 begins to boot

HOWEVER around 30 seconds later one of the capacitors begins smoking and is glowing bright orange.  I immediately pull the power cable out.

The capacitor had disintigrated.  It was one of the two located near the PRAM battery, at spot C184.  C13 was also pretty hot to touch, but may have been because of its proximity to C184.

Original capacitor: 47u 16v

Replacement capacitor: 47u 20L (so 20v?), Tantalum

I desoldered the severely burnt and damaged capacitor at C184 and tried another that was identical to the one that had just self-destructed.

However, now the computer no longer boots or responds to any key-press on the keyboard.  That said, the capacitor was starting to heat up again, so I removed the power.

Any ideas on what would cause this behavior would be appreciated.  Also, I'm wondering if when I was pulling out cables while the one capacitor was glowing hot and smoking I damaged the ADB controller and that is the reason it is no longer powering up?

Thanks

 

[PB145B]

Is your polarity correct? On tantalums the + side is marked with a stripe.

 

[just.in.time]

That was my first thought as well. It appears to be correct though. I took a photo of the originals before removing them to make sure I’d have the correct orientation.

 

[PB145B]

On electrolytics the stipe actually is the “negative” side which is directly opposite of tantalums.

 

[just.in.time]

Oh geeze!  I did NOT know that!  I'm amazed the thing turned on.  Okay, I'll have to do some research and reverse all 5 capacitors.  At least there are only 5.  Hopefully no other components on the board got damaged.

One thing that is strange.  When it worked briefly for ~30 seconds, the startup chime was loud again (had previously been extremely quiet).  Is the audio circuit's implementation not dependent on capacitor polarity, just that there is a healthy capacitor present?

 

[PB145B]

Not sure about that but yeah, I’m very surprised that it even worked at all.

 

[just.in.time]

Good news: After reversing all 5 tantalum capacitors, the computer booted right back up!  And the audio is nice and loud now

Thank you for your help PB145B!

However, Apple Video Player still complains that there is no AV hardware on board.  I didn't recap the tuner card yet, but I figured the RCA jacks would be functional.  Will create a separate thread if a software restore doesn't fix that.

 

[macosten]

Yep, that's one of the trollish things about these capacitors. 

An electrolytic's stripes are negative, and a tantalum's stripes are positive. 

Let this be a lesson to all who wander over here

You could say that this was a ...shocking experience? Or perhaps it was... enlightening?

Nah, but seriously, I wish I knew why they made the stripes as they are...

 

[PB145B]

No problem just.in.time! Always glad to help a fellow vintage Mac enthusiast I’m very happy that it’s working now!

 

[jhorvath911]

Apple video player is not the app the TV uses. You need the specific TV control panel that switches from computer display to TV, and it will work with just the RCA port without the tuner board installed.

Took a few, but here's a link to topic about the software with download link:

https://68kmla.org/forums/index.php?/topic/28181-macintosh-tv-tuner-softwaredrivers/&do=findComment&comment=306219

 

[just.in.time]

Thank you for that link! I spent a while digging around but couldn’t find any TV Setup or Macintosh TV specific download under the North American English or International English subdirectories. Any hints on the name of the download?

 

[just.in.time]

Found TV Setup 1.0.2 on this page:

https://www.fenestrated.net/mirrors/Apple_Support_Area/Apple_Software_Updates/English-North_American/Macintosh/System/Other_System/

Seems to work okay on System 7.5.5.

 

[olePigeon]

You can also attach a digital to analog converter, and get OTA digital channels on your MacTV.

 

[just.in.time]

I may have to find on on Craigslist between that and a PlayStation 2 for games and DVDs, I would be happy to accept the compromised performance/memory limits of this board.

 

[CC_333]

While we're on the topic of OTA TV, the last time I tried watching OTA on an analog-only TV (somewhere between 2012 and 2015 I think-- well past the digital switchover), I was surprised to find that there were still some analog signals up in my area.

Not sure that would be true now, though; I ought to check!

c