[Premium-Rx] Tantalums again

[Dave Schofield]

Further to Dan's comments on the strange leads.
I find the best way to remove the tants from an RA-1792 / 6790, is to cut them of from the top side of the PCB's then while applying heat, pull them through from the underside. Then clean out the old solder with decent quality desolder braid. Trying to do it any other way is, as Dan says, nye on impossible.
For what it's worth as well, I've always found that the newer tants used in the backlit 1792's are a lot less troublesome.

In my early days as a TV engineer, my boss told me "never trust a blue tant"...
Pretty good advice to, they always seem much more prone to fail. Or maybe I've just been unlucky :-)

Cheers,
Dave. S.
www.ra1792.co.uk


Sent from Samsung Galaxy on O2

-------- Original message --------
Subject: Re: [Premium-Rx] Tantalums again 
From: Dan Rae <danrae at verizon.net> 
To: antonio <i8iov at yahoo.com> 
CC: "premium-rx at mailman.qth.net" <premium-rx at mailman.qth.net> 

On 5/24/2012 6:39 AM, antonio wrote:
> Hi all,
>
> I'm going to gradually replace almost all of the tantalums on my 1792.
I did that with my first 1792 because it came to me with four or five 
shorted Tantalums.  It is /not/ something that I would recommend and 
certainly would not do again...  It took me a week of spare time to do 
it.  But this was more than ten years ago, and they were not so easy to 
come by then.

First off, in the 1792, at least all those I have worked on, all the 
through hole component leads have been cut off in such a way that they 
have a kind of "fish tail" at the end and will not pass through the 
holes even with the solder removed.    Secondly there is no heat relief 
on the ground holes, and since the A4 board is extra thick and the holes 
are plated through, all those connections are really hard to undo and 
clean out, even with very good de-soldering equipment.

Since then I have had maybe two or three tants die in my herd of several 
1792s and 6790/GMs and have replaced those as and when needed.

The only time I have seen any collateral damage in either was when I had 
one die in the 20 V power supply which was pretty spectacular since it 
burnt up the printed circuit board, and another on the A6A1 board which 
fried a trace on the A9 board.   That one in the power supply is the 
only one that I think is worth replacing as a matter of course and then 
not with a bead type of tant, since it is not protected by any current 
limiting upstream.

73 - Dan

ac6ao / g3ncr
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