[1000mp] dead tuner

Thu, 4 Mar 2004 22:52:22 -0600

My MP Mark 5 did the same yesterday.  From 28.5 Mhz it reset to 7.000 Mhz.
Why?

Win w0lz

----- Original Message -----
From: "Alex NE7L" <[email protected]>
To: <[email protected]>
Sent: Thursday, March 04, 2004 7:38 PM
Subject: RE: [1000mp] dead tuner

> Thanks a lot Tom,
> I gonna play with this thing when I get into that tuner.
>
> 10m is a strange band for tuner, I believe ... a few months ago my radio
was
> resetting into 7.000 when I transmit on 10m. then it's gone :)
> A month later I got an email from another guy who faced the same effect on
> his MP...
>
> So, anyway, I will open it and check how it works.
>
> Alex,
> NE7L
>
>
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]
On
> Behalf Of Tom McDermott
> Sent: Thursday, March 04, 2004 8:16 PM
> To: [email protected]
> Subject: Re: [1000mp] dead tuner
>
>
> My FT1000MP (pre Mark-V) had the antenna tuner go off into the weeds
twice.
> Both times while trying to tune on 10 meters, near 29 Mhz, into a 2.5:1
SWR.
> The variable capacitors were both fully opened up, and the tuner was
unable
> to do anything regardless of resets. Both times it went back to the
factory
> under warranty, the first time they reset the caps back to partially
closed
> while working on it. The second time they replaced the tuner altogether.
> Have been afraid to use it ever since (especially on 10m)!
>
> About 2-3 years ago I recall reading an article that claimed that the
> problem was that the microprocessor on the Tuner-CTRL board had a poor
> power-on-reset circuit, and that the power fed by the radio to the tuner
> (all inside the radio) ramped up so slowly that the tuner microprocessor
> never went through it's normal reset function when the radio was powered
on.
> He said that resetting the processor caused it to drive the variable
> capacitors to the fully closed stop point so that it knew where they were
> positioned. The author claimed that increasing the capqcitance of the
power
> on reset capacitor of the tuner microprocessor (Q6517) on the Tuner-CTRL
> board fixed that particular problem. I.E. the tuner could find home base
if
> it had driven the capacitors out to minimum capacity.
>
> One should always bookmark or save such an article, because I surely
cannot
> find it now.
>
> In looking through the service manual, the tuner determines it's own reset
> through a pretty flimsy circuit. The timing is set by a 0.47uF capacitor
> (C6559) driving the base of a UN2214 driver (Q6519) on the Tuner-CTRL
board.
> As I recall the article said something about making this 0.47 uF capacitor
a
> lot bigger, maybe 10uF. All this makes me think that perhaps my memory
still
> functions some days.
>
> Before doing any modification, it seems like one could test this theory by
> momentarily shorting the collector and emitter of Q6519 which would cause
> the tuner's processor to reset itself. If that drove the two motorized
> variable caps back to closed, then it would seem to point to the problem.
>
>
> -- Tom, N5EG
>
>
>
>
>
> >Another idea :
> >I remember I've read a posting about some tuner malfunction ...
> >That guy disassembled radio, got to tuner, disconnected-reconected all
> >coaxes and jacks. turned var-capacitor this and that way and it helped...
> >
> >Looks like I gonna do the same if memory reset woodoo would not help.
>
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