[Premium-Rx] Desoldering [WAS: Tantalums...]

[Bob Betts]

Bob:
Interesting experience, for sure.
I wasn't as lucky. On my 6790, which went dark last week, I had isolated the short on the +15 rail to the A8 board by selective interconnect unplugging. I think there's 9 tants there and I found it after desoldering 3 of them. If I had the time, I'd be in there replacing all of them...one board at a time. 
I had considered unsoldering the output side of the TO3 regulator and connecting a 10 Amp supply...just to find the bad cap. But I was concerned about doing other damage. I'm not sure what else could be affected, but it sounded like too much fun to be safe.
Anyhow, ain't it nice when you flip the switch and everything is normal again?
 
Bob, N1KPR
 
http://www.bobsamerica.com/racal-mod.html



--- On Thu, 5/24/12, Robert Nickels <ranickel at comcast.net> wrote:


From: Robert Nickels <ranickel at comcast.net>
Subject: Re: [Premium-Rx] Desoldering [WAS: Tantalums...]
To: premium-rx at mailman.qth.net
Date: Thursday, May 24, 2012, 6:30 PM


I'll show off my favorite "bad tant" picture from a recent RA6790 repair:

http://img10.imageshack.us/img10/4559/badtant.jpg

This one failed during the repair process, as all of a sudden one supply 
rail was dead, although it had been working minutes before.   I just 
happened to look in the right spot and did a double-take when I saw a 
little ball of solder dangling from one blue tantalum...and more to the 
point, the direct short caused by the one before it.

Most tantalum failures are not this visible.  One of the modern 
inexpensive IR thermometers is a useful addition to the workbench - I 
well remember the painful finger burns from my previous method.

73, Bob W9RAN
______________________________________________________________
Premium-Rx mailing list
Home: http://mailman.qth.net/mailman/listinfo/premium-rx
Help Page: http://mailman.qth.net/mmfaq.htm
Post: mailto:Premium-Rx at mailman.qth.net
Help Contact eMail:  paul at 8zo.com
Home Page:  http://www.premium-rx.org/