Teac AG500

[Gary Woodruff]

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

[abrsvc]

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

Dan

[Arfa Daily]

"Gary Woodruff" <woodruf...@gmail.com> wrote in message
news:s6dyp.20195$Ot6....@newsfe15.iad...

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

[abrsvc]

On May 10, 9:19 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:
> "Gary Woodruff" <woodruffrep...@gmail.com> wrote in message

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

[Arfa Daily]

"abrsvc" <dansabr...@yahoo.com> wrote in message
news:f5e7981a-2aad-4817...@f9g2000vbz.googlegroups.com...

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

[Mark Zacharias]

"Arfa Daily" <arfa....@ntlworld.com> wrote in message
news:R6Gyp.53$Ky...@newsfe24.ams2...

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.

[Gary Woodruff]

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

[abrsvc]

On May 12, 1:14 pm, Gary Woodruff <woodruffrep...@gmail.com> wrote:
> Mark Zacharias wrote:

> > "Arfa Daily"<arfa.da...@ntlworld.com>  wrote in message
> >news:R6Gyp.53$Ky...@newsfe24.ams2...
>
> >> "abrsvc"<dansabrservi...@yahoo.com>  wrote in message

> Gary- Hide quoted text -
>
> - Show quoted text -

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
11-15.

Dan

[Arfa Daily]

>>
>>
> 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
>

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