[ICOM] 706 MK2G Finals - possible replacements?

[D C *Mac* Macdonald]

While I don't know the specifics of replacing the
transistors in the 706, I can tell you that suface
preparation is paramount.  Mounting surface
must be smooth, clean, and pre-tinned with
solder.  Quick tinning of the transistor leads
prior to installation would also be advisable.

Pre-bend the connector tabs a bit so that they
will have spring tension when the actual body
of the transistor (pre-coated with heat sink
compound, of course) is fastened to the board.

When soldering these dudes in, it is mandatory
that you use a soldering iron with adequate heat
(probably 100W) and a tip with great enough
mass to maintain its heat before the connection
is made.  If the heat/mass combo is sufficient,
you should not have to apply it more than a few
seconds.  The width of the tip should probably
be about 50% wider than that of the transistor
tabs you plan to solder.

I replace VHF and UHF power transistors regularly
at work but they run at about a power level of
40 Watts PEP out.  I have read that AM operation
of an IC-7000 should not exceed about 25-30 Watts
of carrier to keep dissipation within limits and maintain
a clean output signal.  I suspect the same would be
true of a 706.  This leads me to estimate that the
transistors in the 706 would probably not be greatly
larger than those with which I work regularly.

YRMV (Your Results May Vary).

Good luck and 73.

Mac - K2GKK/5
Oklahoma City



----Original Message Follows----
From: "David Ring" <djringjr at gmail.com>
Reply-To: ICOM Reflector <icom at mailman.qth.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Subject: Re: [ICOM] 706 MK2G Finals - possible replacements?
Date: Thu, 11 Jan 2007 07:10:28 +0800

You might consider the difficulty in soldering the "wings" of the
transistors, often the amount of heat needed to solder them to the
circuit board is sufficient to harm the transistor.

I've replaced these before - and by the time I was done with shorting
two of them, I considered that $300 to have ICOM do it for me, was a
reasonable price.

It is difficult to discover on your own the combination of wattage and
tip size needed to solder these.

At least it was for me - I used a soldering iron too small the first
time, and by the time I got the wings hot enough to solder, I had done
damage by the time I had gotten all four of the wings soldered.  I
then used a 200 watt iron and inexperience  at heat sinking the
transistor while I soldered resulted in the second failure.  The third
time I did the repair worked fine - but by that time I had ruined
several transistors.

Perhaps someone can give you some pointers - there must be a secret to
doing this!

73
David Ring, N1EA