On May 10, 9:19*pm, "Arfa Daily" wrote:
"Gary Woodruff" wrote in message

...

Hello all, I have a Teac AG500 that will not switch between inputs. The
CD and Phono indicator lights are both lit. When you try to select tuner
the indicator lights momentarily then goes out(leaving CD and Phono
lit). It does play audio through the CD input. I have checked all
resistors and tact switches on the front panel board all are good. I am
leaning towards the IC on the mainboard that switches the inputs but do
not have a print and am not sure which IC it is! Any and all help is
greatly appreciated.

Thanks, Gary

It's a nice thought, but I would be leaning more towards it being the system
control micro, as there is an issue with the function indicator LEDs, as
well as the actual switching. It will be the micro that is responsible for
generating both the LED drive signals, which will likely be linear
one-for-one, and the control signal for the source switching IC, and this
signal will probably be I2C.

Have you looked with a 'scope at the actual matrix lines for the front panel
tacts ? As well as stuck switches, I have also had leaky switches, and leaky
caps across switches. If it is one of the systems that uses a resistor
ladder and an A-D input on the micro to determine which button has been
pressed, these can get mightily upset with leakage amongst the wanted
resistance. I know you say that you have checked the Rs on the front panel,
but have you checked every one carefully for value ? Do other switches do as
they should ?

Arfa

Arfa,

While I agree that your diagnosis is possible, experience tells me
that the switching IC is the most likely culprit here. I would
mention that checking for filter caps on the 5V line would also be a
good idea.

Dan