[Fourlanders] FT-920 problem

[Roger]

Bob,

If the 920 was working for a number of years, I would suspect something has
changed in either a menu setting or there is a hang-up in the rig
microprocessor.  If you haven't made any menu changes, then resetting the
internal microprocessor would be the next thing I'd try.  I'm not familiar
with the 920 menus or how it is reset.  There are probably two "resets", one
more thorough than the other.  I'd do the more thorough one, but you will
lose all of your custom settings.  Maybe write down all of the custom menu
settings you have now, and then reset.

Roger, K4RW

-----Original Message-----
From: fourlanders-bounces at contesting.com
[mailto:fourlanders-bounces at contesting.com] On Behalf Of Bob Lear
Sent: Wednesday, August 15, 2012 10:28 PM
To: fourlanders at contesting.com
Subject: [Fourlanders] FT-920 problem

I have a problem with my Yaesu FT-920.

About 10 years ago, I added transverter ports to my 920.  All I did was put
a DPDT relay inside to switch the low-level signal lines for RX and TX that
go from the main board where the ~1mW TX signal originates before going on
to the PA module and the received RX signal comes to the main board after
coming from the BandPass Filters.  These lines are fed with mini coax to TMP
connectors.  I also broke the T12 line to the PA board to shut it off
completely when using a transverter.  I had previously done the same thing
to an Icom IC-736.

All was well with both radios and were used extensively with transverters
for many years.  Then a problem appeared with the 920.  I wasn't getting any
TX output to a transverter, but RX was working fine.

I at first blamed the problem on a faulty relay, but after replacing it,
found that I still had the problem.  At the same time, I modified another
920 for a friend in exactly the same way, and it also would RX but not TX to
a transverter.  When the relay is switched to normal operation mode the
radios (920's) both operate on HF/6 as normal with full 100W output.

Now I have narrowed the problem down to something like the ALC folding back
the output power when in transverter mode.  I checked the output power at
the TMP connector going to the PA board using a Boonton microwattmeter.  In
normal mode the power is just over 1 mW driving the PA to 100 W.  In
transverter mode, the steady state power out is folded back to just a few
microwatts.  I can see on the analog meter on the microwattmeter that on
first key down, the meter starts to jump up, but then it drops back,
indicating that the ALC/SWR/Temp power reduction circuitry is doing
something to reduce the power.

I really don't think I understand ALC circuitry and would like to have some
help to figure this problem out.

The strangest part is that my 920 worked fine with transverters for so many
years and then changed.  The second 920 had reduced output immediately after
I put in the relay/modifications.

I have a three page pdf schematic set for the 920.  Can't attach it on the
reflector, but if anyone is interested in helping me out, I can send it
separately.  On page two of the schematics (main board), all the
modifications are on the left side, the TX out in upper left and RX in below
are where the relay is inserted.  Lower down, on J1014 is where the T12 line
goes out to the PA unit.  That had a switch inserted there at the connector
to open the T12 line to the PA board for transverter operation.

Thanks for any help you can be on this.  Bob W4ZST
_______________________________________________
Fourlanders mailing list
Fourlanders at contesting.com
http://lists.contesting.com/mailman/listinfo/fourlanders