Fisher CA-283

[Michael Fiedler]

I am working on a Fisher CA-283 amplifier, without a diagram. I have
repaired the problem of the channels intermittently dropping out, and
now have one problem left to solve: when you select Video Aux, and
then select tape monitor for inputs, the LED for Video Aux stays lit,
even though you have tape monitor selected (it is lit also). There
must be a chip on the unit that is defective that is causing this
combination. Anyone have any ideas of which chip it is? Any pointers
appreciated. Thanks in advance.

Mike

 

[JURB6006]

Stand up board has a chip, I think a TC9164 (9163?). This is the board with the
input jacks on it.

It's been awhile but IIRC this chip runs the LEDs, and is either logic or bus
controlled. I've replaced more than one of them for this kind of problem.

Shouldn't be too too hard to get, I've seen them in other brands, and again
IIRC they cause similar symptoms.

JURB

 

[Michael Fiedler]

Stand up board has a chip, I think a TC9164 (9163?). This is the board with the
input jacks on it.

It's been awhile but IIRC this chip runs the LEDs, and is either logic or bus
controlled. I've replaced more than one of them for this kind of problem.

Shouldn't be too too hard to get, I've seen them in other brands, and again
IIRC they cause similar symptoms.

JURB

The only chips on the input board are an LC4066 (which is the one I
suspected) and an LC7815 (which sounds like a voltage regulator chip).
We have some of the 4066's at work that we use in our audio console,
and they are a type of logic chip. But I think the 4066 is the chip
you are trying to refer to.

Mike

 

[JURB6006]

But I think the 4066 is the chip

you are trying to refer to.

Mike

I was doing this from memory, I haven't worked on one for a while. If it uses
4066s then the fault is probably with the micro. The 4066 is controlled by
logic levels, not a data bus. I would look for shorted clamping diodes on those
control lines before looking for a micro. There may even be driver transistors
which should be checked.

JURB

 

[Mark D. Zacharias]

4066's are VERY cheap - worth a try replacing that, I would say.

Mark Z.

 

[Michael Fiedler]

4066's are VERY cheap - worth a try replacing that, I would say.

Mark Z.

I replaced the 4066 today (it is a quad bilateral switch) and that
didn't fix it, but another guy e-mailed me part of a schematic. I
have checked all transistors, diodes and board traces, and by looking
at the schematic, I would definitely have to say it's the
microprocessor, the LC7815. I'll have to price one tomorrow to see
how much they are. Thanks to everyone for their help.

Mike

 

[Lawrence]

The old saying comes into play here: If it ain't broke, don't fix it.
What you are seeing is the way that unit is supposed to work. I own a
CA-271 amp. The reason the light stays on is so you can tell which device
you will be taping from if you were to start taping something. That is
also why (on my unit anyway) the wording for Tape Monitor is in red while
the other device settings are white. I know how much of a pain it can be
having your head in a unit for what seems like ages just to find out you
didn't need to be.
Hope this helps.
Lawrence

 

[Michael Fiedler]

The old saying comes into play here: If it ain't broke, don't fix it.
What you are seeing is the way that unit is supposed to work. I own a
CA-271 amp. The reason the light stays on is so you can tell which device
you will be taping from if you were to start taping something. That is
also why (on my unit anyway) the wording for Tape Monitor is in red while
the other device settings are white. I know how much of a pain it can be
having your head in a unit for what seems like ages just to find out you
didn't need to be.
Hope this helps.
Lawrence

A voice of sanity! Because I was not that familiar with the unit and
because the person I am fixing it for indicated a problem with the
lights jumping around (which I haven't seen yet), I assumed that this
WAS one of the problems. Yes, I was way into it, thinking beyond the
box, instead of thinking of something simple. Now, all is well.
Thanks greatly for your sane, simple input, and thanks to all the
others who weighed in on this one.

Mike

 

[JURB6006]

Wow, OK. I inferred from the original post that there was abnormal behaviour of
these LEDs. Yes the tape and any <u>one</u> other source LED can be lit. I have
seen them act up where some would be on all the time and the input switching
was screwed up as well.

Of course you might find later that it does have an intermittent problem of
this nature.

JURB