More new information:
When I mentioned that the encoders work for the first second or so after the
boot sequence has completed, the “A” is selected. When the S meter “bump”
occurs=, then “B: gets selected on the display, and the encoders stop working
for 15 minutes.
When the radio starts to operate correctly, it is still in the “B” mode so the
band buttons change the band of the sub receiver at this point. Pressing the
A/B button for two seconds corrects this situation and the band buttons then
control the main receiver.
I am pretty sure the problem is not in the 4 to 16 line multiplexer as this is
an output that selects which switch is being read at a given moment. Even if
that chip were operating improperly, the A/B switch would need to be pressed
(or shorted) in order for the “A” to “B” transition to take place.
Gary
PS: This radio probably is not really worth all this time but I am learning a
lot about the operation of radio control circuitry so this exercise is worth
the effort for that reason. Maybe my observations help others as well...
> On Aug 9, 2016, at 7:13 AM, Jeff (W4DD) <w4dd09@gmail.com> wrote:
>
> The binary number that the B represents may provide some insight.
>
> On Aug 8, 2016 11:25 PM, "Gary J FollettDukes HiFi" <dukeshifi@comcast.net>
> wrote:
>
>> There is some new information.
>>
>> The A/B switch, when held for 2 seconds, is supposed to change the “A” or
>> “B” on the display and this in turn makes the band select buttons select
>> the band directly. It is supposed to default to “A” I think. Mine defaults
>> to “B”.
>>
>> If I wait the 15 minutes, and the encoders start to work, I can use the
>> A/B to select “A” but upon restart, the default becomes “B”, which is
>> incorrect.
>>
>> I think the 15 minutes, a rather consistent number, may be a timeout for
>> the interrupt lines.
>>
>> It would appear that something is pulling the A/B switch line low, but it
>> is not the switch itself. The switch works fine once the timeout takes
>> place.
>>
>> I am now looking at the 74HC154 4-to-16 line decoder/demultiplexer.
>>
>> More to come…
>>
>> Gary
>>
>>
>>
>>> On Aug 8, 2016, at 3:29 PM, Stuart Rohre <rohre@arlut.utexas.edu> wrote:
>>>
>>> Gary, before you shotgun all the capacitors, look at all the solder
>> joints for the affected boards with a high intensity light, and a
>> magnifier. A head mount magnifier with light may work, but I often use and
>> independent high intesity Halogen light we bought for troubleshooting.
>>>
>>> I am betting on one or more bad solder joints. How old is this radio?
>> Are you the first owner?
>>>
>>> Stuart Rohre
>>> K5KVH
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