[ICOM] 706 MK2G Finals - possible replacements?

[David Ring]

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

> On 1/11/07, Dan Doss < kg0mm at arrl.net> wrote:
> > Hello all,
> >
> > First off let me say that I'm relatively new to the reflector so please
> > excuse any redundancies in what follows on the subject. That being said -
> > I, like many on the reflector, have had to replace the HF finals on the
> > 706. The last time I did, the original SRFJ7044 MosFET's were available
> > from Icom, albeit at a premium price. A call to Icom yesterday brought me
> > aware of the fact that these transistors are available only for repairs
> > made by Icom services centers. This fact may already be known by many, but
> > was a little disconcerting to me. I was told that the only way one (an
> > individual) could repair their blown finals was to buy a complete new PA
> > assembly. I was given a part number of 98414684 (which is available) and
> > lists for $293.33. Yikes! I was also told that the finals used on the new
> > PA assy were not "compatible" with the older boards. When asked if this was
> > due to electrical or physical reasons, the nice parts lady indicated that
> > she thought is was because of physical differences. This was not confirmed
> > by an Icom tech.
> >
> > After a bit of research, I found that the SRFJ7044 MosFET is packaged in
> > what Motorola/Freescale/MA-Com calls "Case 316-01". This is a 6-legged
> > package with is attached to the heatsink with two screws. Other similar
> > MosFET's (such as MRF150) use a stud-mount style package. I have not seen
> > what transistors are used on the new style PA. There may very well be both
> > physical and electrical differences between the two parts. Without having
> > data sheets on either, it's difficult to ascertain if an off-the-shelf (and
> > still in production) replacement part exists. I seriously doubt that Icom
> > would be the least bit interested in locating such a device.
> >
> > Not to be too long winded about the subject, but at a repair cost of nearly
> > $300, it might be worth it to the group if we could attempt to locate
> >  another non Icom-specific part to repair our rigs with. If anyone has
> > access to a network analyzer (and a spare '7044), it should be possible to
> > characterize the old part so that a potential replacement could be
> > researched. A quick search on MA-Com's website yielded a couple of
> > transistors of the same power class and package that _might_ have similar
> > characteristics (s-parameters, etc) to the '7044. I would be willing to use
> > my 706 as a "test bed" for the cause if we can get some specs on the old part.
> >
> > Let me also say that I am not in the business of repairing radios for hire.
> > I just hope to spark some interest so that we might be able to keep our
> > venerable 706's running without having to break the bank for repairs or as
> > might be hoped by some, buying new rigs...
> >
> > Any thoughts???
> >
> > 73,
> > Dan - KG0MM
> >
> >
> > ----
> > Your Moderator: Dick Flanagan K7VC,  icom-owner at mailman.qth.net
> > Icom Users Net: Sundays, 1700Z, 14.316 MHz
> > Icom FAQ: http://www.qsl.net/icom/
> >
>
>