[Yaesu] FT-757GX problems. XE3WR

[certified-electronics at juno.com]

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Rolando, 
Wow.  Sounds familiar.  First thing I will tell you when working on a
FT-757 is be very careful.  You can start out with one problem then
before you know it you have a slug of other problems from loose
connections and the small plug in connectors becoming intermittent.
So be careful.  The diodes I was referring to wold not cause the problems
your having.
Sounds like most definately you have a losss of voltage if the display
isn't coming on properly.
There is a 5v regulator in the front of that set but without the
technical supplement in your
hands, I'm afraid to direct you there right away.

Rolando, you're gong to need the FT-757Gx technical supplement.
It's a must.  I ran into a similar problem and found a burned trace on
one of the circuit boards.  If I remember correctly the circuit trace ran
13 VDc across the board to the front of the set into a voltage regulator,
it then provided 5 volts for several more I.C. chips the computer CPU and
god only knows what else.

Well to make a long story short.  The CPU was also bad and I'LL have you
know they are NO LONGER AVAILABLE ANYWHERE. When I turned the main dial
the rig would jump all over the place and the CPU was totally confused.  
I bought a junker 757Gx locally that had a good CPU, installed it in my
rig, replaced the 5v regulator and repaired the trace and things started
coming back to life.
Jusdt as a note to anyone with a 757, if you have a catostraphich failure
of the 757 CPU, don't waste your time allking Yaesu for the part.  THEY
DON'T HAVE IT ANYMORE.  They told me even if they did have the chip, they
had no way to program it.  So be very carfeul when working in your 757
when it's on.

Don't ask me how they did it Rolando, but the previous owner cranked it
up on 11 meters
running AM  trying to run the rig at full output power apparently for a
long period of time too
and it just can't be done.  Evidence of this can often be seen in the RF
deck, look at the  toroidal transformers associated with the upper bands
(10 meters.)  I've seen these toroids
often blackened and they crumble in your hand when touched.
It's just unbelievable what can go wrong or burn up when a rig is abused.

Don't know if that is of any help to you Rolando, but get the technical
supplement for your rig for starters.  
After you remove the top and bottom covers, the front panel  of the 757GX
pulls forward after you loosen two screws on each side of the rig. This
allows for better access to the boards and you can
get behind the front panel.  If you start pulling plugs and cables in
order to service your any of the boards.  Make darn sure you label your
plugs and cables so you remember where they came from.

Best 73s for now.
Carol Maher
W4CLM





--- In ft-101 at yahoogroups.com, Rolando Rivas <xe3wr at y...> wrote:
> Carol,
> 
> A friend of mine give me a ft-757 to look inside, the
> rig is dead, not even the display works, sometimes
> ligths up but barely displays all the leds inside at
> the same time...
> 
> these rig used to be from a CB'er, are u suggesting
> that i can start looking inside those diodes to look
> for failure?
> 
> i have also read that that rig also looses voltage on
> a regulator that powers the display causing it to go
> dead...
> 
> anyhow, i´m starting to get into semiconductors and
> still i have not dinished the aligment for my
> ft-101ee, but i know it works, 1 CW contact with my
> baby boy 8 months old on my arms... it´s been 9 yearse
> since i did´t do it, that prooves a lot.
> 
> many thanks to all the people who support us on these
> great great egroup.
> 
> sincerely:
> 
> rolando
> XE3WR
> .- .-.
>