Teac AG500

I believe that these use a TC9163 switching IC. If this is not present, list the 16 pin ICs close to the inputs.

Dan

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

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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

With the majority of input switching schemes that I see on hifi equipment, the front end selector IC is responsible for for just signal switching, and is an I2C driven device. Indicator LEDs are almost exclusively driven in a fully linear fashion, straight from a port on the system control micro or, if there is enough of them, via a bus expander IC. I'm struggling to see how a defective input switching IC, would affect the function indicator LEDs in the way the OP described, unless you're thinking that the LEDs on that model - which I admit that I don't have schematics for - might be being driven by a few 'spare' channels on the switching IC ? Looking at, for instance, the AR600, LED function indicator switching is completely separately handled to signal switching. The LEDs are driven directly by the micro. Of course, if the AG 500 is well known to you, then I bow to your knowledge of it, and its common faults. I agree with you that checking the 5 V rail for level and noise, would also be a good move.

Arfa

Some input switch IC's do also run front panel LED's. Saw one just the other day. Can't remember the IC number, though.

Mark Z.

Hello all, The IC is LC7818. I hope that helps point us in the right direction. I do have a scope but it is unreliable and am hoping to solve the issue without it. Thanks for all the help, Gary

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Thanks for the update. Yep, thats the other "popular" one I tend to keep in stock.

In regards to checking this. Using a scope, chekc for a signal on pins 6 and 23, These are the "tape out" pins for left/right. You should always have a signal here that mimics the selected input. The inputs are on pins 1-5 and 26-30.

Please note that the LED display is controled by the state of pins

Dan

Ah. A 7818. That one does indeed have drives for indicator LEDs, in which case I concur with abrsvc's contention that this is the most likely cause of the problem.

Arfa