I think you may be on the right track. Several older Yaesu
transceivers I owned or have worked on had miniature
'grain of wheat' pilot lamps in series to act as fuses and
spare the primary winding on the input transformer.
I would guess that is the most likely component to blow.
If yours is open, you can obtain more from Radio
Shack, but note carefully that probably most small
pilot light types selected at random may have too tough
a filament, and might not fuse open like the original parts
do. Some hams just jumper past a blown lamp on the
theory that any replacement might not blow prior to
transformer/FET/diode damage anyway. Always best
to get an exact replacement from the manufacturer,
but this is often not an option with older radios.
If the obvious is not your problem, especially a fuse
lamp, it would not hurt to do a quick check of the
supply voltages in the radio. BTW, a good quick
check would be to verify that the radio will still
transmit normal power levels into a dummy load.
If that is the case, you may find all voltages in the
receiver are normal- but look carefully at bias
voltages in the RF amp circuit for any obvious
tipoffs. You may find your FET is shot.
Having a schematic for the radio would make things
a lot easier, though you might get by with just
circuit tracing. If your radio has protective diodes
across the antenna input, one of them might have
been damaged and ended up close to a dead
short. Easiest check is probably to simply desolder
and lift one end of each diode. We often see 'back-
to-back' diodes paralleled across a receiver input line.
Other possibilities might include dirty relay contacts
(cycle the relay repeatedly while listening to one of
those 'weak' signals). Then possibly try replacing the
input amplifier, often a discrete FET. Last but not
least, you could look for an open circuit in the
primary (ant) side of any input transformer. BTW, you
have checked your antenna/coax setup to the radio by
substituting another known-good radio, to rule out
coax or antenna problems, right? :o) Good luck, 73,
David K3KY
Date sent: Mon, 19 May 2003 17:38:55 -0500
To: yaesu@contesting.com
From: David Vondrasek <n5ito@davidv.net>
Subject: [Yaesu] FT-757GX No Recieve
> Does the FT-757GX have any overload type fuse on the recv. end ? My revc is
> WAY down a normal 60 over S9 is S3-4 and unless your 60 over I don't hear
> you , after a local ham keyed up with 1500 watts and we are REAL close.. I
> think it killed the front end. I know a lot of radios ( FT-101) have a
> overload fuse type thing.. ANy suggestions ??
>
> Dave
>
>
>
> David L. Vondrasek
> N5ITO Amateur Radio Call
> AAR6NM Army MARS Call
>
> _______________________________________________
> Yaesu mailing list
> Yaesu@contesting.com
> http://lists.contesting.com/mailman/listinfo/yaesu
|