[1000mp] dead tuner

Thu, 4 Mar 2004 20:38:00 -0500

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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