Mark Zacharias wrote in message
.com...
"N_Cook" wrote in message
...
First of these looked as though a failure of the tuner block. Owner
bought
another one for spares, removable front display missing.

This one has exactly the same fault symptom so more likely a problem
with
the front panel (or improbable same tuner fault on 2 separately acquired
units).
Tuner will go into auto strongest signal search and store in memory and
also
readout follows manual input of frequency and stores in memory but at no
point does the audio come through to the output amp.
Pressing the presets shows the frequencies but no audio. Injecting local
modulated RF in there and audio is outputed and stays invariant on
pressing
any preset so stuck on one RF tuning setting. So not a false muting
problem

Some of the main chip SM solderings seemed suspect so redid the non LCD
segment ones. Cleaned the 14 pin front to interior header plug. No stuck
closed keys. It looks as though the front has been kneed at some point
as
the ring around the rotary encoder button is cracked but no pcb problems
found.
The LCD clock, CE and data lines between the 14 pin header and the 64
pin
chip trace through. Not possible to scope anything on the board without
making up a one-off extender cable.
I'm assuming some data problem but what changes between sending data to
and
from the tuner to load the presets and normal listening mode?
Schematics are out there for this model



Not totally out of the realm of possibility that the two could both have
bad
front ends. Have you tried applying an external tuning voltage?

Mark Z.


I did with the original one and you can manually tune via a 10 turn pot to
change stations with audio emerging from the pa. No reason to assume any
different with this one but as awkward to get to I will leave as is



Another possible variable is battery B+ but there is good regulation . With
no key presses the micro-sourced voltage is between 4.81V and 4.83V with no
power output , and invariant with "battery" between 12V and 14V

Measuring the keyed voltages , K-0, for the front buttons, pulls down to
left buttons 1.14,.60,.03V
central 1.50,.81,.33,2.57,3.69 V
right 1.83, 3.37, 3.00 V
I wonder what the acceptance bands for each of the 11 functions is in the
look-up table. I will guess at 1/3 of an interval with 1/3 for gaps for
unplaced or perhaps error so about .1V out and problems can ensue.
Will have to see if those voltages agree with the resistance chain, not
simple correspondence nor necessarily linear intervals. Minimum gap is .81 -
..6 V which looks suspicious at this stage. K-1 is similar resistance change
system for the other more minor function 8 buttons, I suppose I had better
check those also