AGC to fast
- Hello all, I wonder if anyone has experienced what
I have with my 897 (1.5 yrs old)
Agc fast and slow settings work but slow is not quite
slow enough. Strong signals are a little distorted. I have
to use the attenuator and/or back off the rf gain
considerably. If I A-B it with my IC706 the difference
is night and day. The 706 with full rf gain and even with the
pre-amp on produces very smooth audio.
Is the agc adjustable through the service menu or perhaps
an internal pot to tweak?
Unfortunately my FT-897D hasn't arrived from eBay yet. But I used the
sparetime and had a closer look to the FT-897 servicemanual these
As the circuits are similar on the models FT-8x7, we can use my FT-
817 AGC-fix for the FT-897 too. It should be easy done on the FT-897
as the parts are seen without the need to remove a PCB unit and the
soldering should be done as easy too.
Slower the "AGC SLOW" time constant
- C1503 (1µF) -> 4.7µF parallel
- R1479 (10k) -> 1k parallel
Servicemanual, page 23, upper middle (below socket J1005)
You can locate both of these parts when you open the FT-897 and have
a look to the MAIN UNIT. The VFO looks toward to you, the backward
sockets are still on the backward side.
So you have to look just below the PR DATA socket (J1005). You should
see 2x SMD electrolyts on the lower left corner (left of them is
crystal CD1002) and 2x 5-pin ICs (Q1100, Q1095) on the lower middle
side of the PR DATA socket.
So the right one of those both electrolyt is C1503. On it's upper
right edge there's R1479 going horizontally to Q1100 on it's right
Or in other words again. Locate the lower left corner of PR socket
J1005. You should see the crystal (or resonator ??) CD1002. Now from
left to right: CD1002 -> C1491 -> C1503 (!!) -> R1479 (!!) -> Q1100.
Everything OK !? I think so....
Adding a parallel capacitor to C1503 had solved the "too fast AGC" on
my FT-817 well but sometimes I would like an even slower AGC. But
here there should be enough room for experiments. A value of 4.7µF
should be a good start (..or the final solution, hi.). Just monitor
some "problematic stations" on SSB and hold a small electrolyt or
tantalum parallel to C1503 while listen to the RX sound. Then you
should hear the improvement. You can try a 10µF too of course, but
the S-Meter would get slow too (never forget) !
If the stations still would produce some audio distortions while you
just have 4.7 or 10µF parallel you could hold a resistor of 1k
parallel to R1479. This might reduce only the strong signals a little
When I will get my FT-897D I will do that mod too (as I expect the
same bad SLOW AGC like on my FT-817). Then I'm able to take some
digital pictures and write a better modification sheet.
Please tell about your experiences here with that mod !!
--- In FT897@yahoogroups.com, "Dave Campbell" <wcampbell@o...> wrote:
> Hello all, I wonder if anyone has experienced what
> I have with my 897 (1.5 yrs old)
> Agc fast and slow settings work but slow is not quite
> slow enough. Strong signals are a little distorted. I have
> to use the attenuator and/or back off the rf gain
> considerably. If I A-B it with my IC706 the difference
> is night and day. The 706 with full rf gain and even with the
> pre-amp on produces very smooth audio.
> Is the agc adjustable through the service menu or perhaps
> an internal pot to tweak?