14 Feb
2010
14 Feb
'10
10:45 a.m.
Dwight,
There was some criminal stuff going on with electrolytes in this era, from the asian
manufacturers. Almost everybody associated with the type of electronics that was not
'throw away' remembers this. I had a note from a pro video repair shop, saying
that to get a $15,000 pro video camera back in operation would require the replacement of
all the tant caps, as they were all destined to fail, and yet another trip to the shop.
Anybody else recall this? There was one chemical manufacturer pinpointed, that was
supplying XR7 or whatever electrolyte to all the manufacturers. They shortcut their
process and cut costs, and several years of electronic products were affected.
Please pots your analog computer work! Have you read the Electronic Research Associates
books out there (IIRC)
Randy
From: dkelvey at hotmail.com
To: cctalk at classiccmp.org
Subject: Getting to dislike tantalum caps
Date: Sun, 14 Feb 2010 08:17:28 -0800
Hi
I begining to dislike these things.
I recently got an old 2090 Nicolet DSO ( Digital scope ).
When I got it, it had a blown tantilum on the 5V
for the I/O section. I fixed this and the blown regulator
along with it.
I originally got it so that I could display things from
my analog computer ( That I'm having fun with ).
I powered it up and was just getting the parameters
right for a nice Rose Engine display when the display
went to a defocused dot.
I spent the next few hours trying to figure the best
way to disassemble this puzzle box. I know scope have
to be compact but it would be nice if there was some
thng that said, do this first then this and then this.
In any case, I figured that it must be something in
the main frame, because the display was completely
dead.
I found the failing area and measure some supply lines.
Sure enough, a -12V was missing from the D/A's.
It was run by a local regulator from a +18V line and
that was dead too.
Some more tracing and disassembling, I followed the
short to the input module. I wish I'm know this from
the start. The input module is easily removed. I should
have followed the first rules of trouble shooting, isolate
the parts first and have the minimum connected.
Now, I'd disassembled the entire mainframe that I'd
have to put back together later.
The input module is a pain to take apart. A number
of places, they soldered grounding straps. After unsoldering,
I traced it down to a cap on the common mother board.
I reassembled everything and just had it running for
about 10 or 15 minutes and the screen went to a fuzzy
dot again.
This time, I was smarter. I pulled the input module first.
This restored a nice focused dot in the left lower corner.
I quickly located the next shorted cap and put the unit
back together.
It has been running now for several hours. I just hope it
doesn't blow another cap but I'm sure it will.
As you can see, my love for old tantalum caps is lost
it luster. I wish there was some way to get them to
fail at one time, but then I'd had to do tricks to find a
multiply shorted line ( I can do that but it is a lot of
pain ).
Dwight
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