[Yaesu] 1000MP - Decreased Signal Strength on Low Bands

[Tyler Stewart]

Try using the RX In jack and see if everything sounds normal.  If so, it
sounds like a bad high pass filter section.  The RX ANT In jack bypasses
this board.  This is on a separate board before the main RX RF board and I
believe is only IN when in TUNED mode and is not in line when using a RX
antenna. If it still occurs, I almost guarantee, it's the 80 meter BPF
section in the receiver.  Note that the BPF's are always in no matter what
preamp you are using.

I've had problems with this and some of the bandpass filter sections in the
receiver.  What I've found every time is that the little molded coils they
are using short out some turns.  It's not something you can find visually.
You have to  start lifting leads and measuring or just shotgun replacement.

I just dug out my tech manual for the MP and have noted that L3503 on the
HPF-UNIT is the first coil to ground in the 80 M HPF and has failed once on
both of my MPs!  It's a 1.8uH rf choke and it's Yaesu part # L1790049.

Note that this is a very easy board to work on.  It's located near the right
rear top of the radio behind the AFC board and just in front of the A/B
relay board in front of the SO239 jacks.  It's mounted on a couple of
plastic, snap-in standoffs and the board should be marked with the L3503
designator.

SHould be an easy fix if you can handle basic electronic repair!

73, Ty K3MM



----- Original Message -----
From: "Ken Claerbout" <K4ZW@Staffnet.com>
To: <yaesu@contesting.com>
Sent: Monday, January 01, 2001 2:28 AM
Subject: [Yaesu] 1000MP - Decreased Signal Strength on Low Bands


>
> I noticed during the CQWW CW contest this past November, that signals on
80
> meters seemed unusually weak.  With all the solar activity going on that
> weekend, I wrote it off to poor conditions.  Thinking about this a bit
> further, I recall that over the past month or two, 80 meters has sounded
> unusually quiet.  I decided to do a side by side comparison with my
Kenwood
> 940 and promptly noticed that signals on 80, including power line noise,
> were 20 dB weaker on my 1000MP.  No wonder I was having a hard time
chasing
> the weak DX stations!  Taking a closer look, I also see this happening on
40
> & 160 although it was not apparent until now.
>    I swapped the two rigs just to eliminate any potential problems with
> cables, filters, or something specific to that operating position and the
> problem followed the radio (1000MP).
>     The radio is set for a tuned front end and when I switched it to flat,
> using the broad front end amp, signals came back up on all three bands.
> This would seem to indicate that there is a problem with the low band
tuned
> RF amp.  However, the diagram in the manual labels the range for this amp
as
> 1.9 - 7 Mhz.  Is this front end section actually in use on 160 meters in
the
> 1.8  - 1.9 Mhz range and also on 40 meters between 7 Mhz and 7.3 Mhz or is
> the wide band amp used in these frequency ranges?  If it's the latter,
then
> that kind of kills my theory about the low band amp.  Is there anything
else
> setting wise etc. that I should be checking?
>     In the event I have to get this repaired, I'd appreciate suggestions
as
> to where I should have this done.
>
> 73
> Ken - K4ZW
>
>
>
>
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>


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