This unit has been a major pain.... the original symptom was the sound
cutting out on both channels. It would run normally for a while and then cut
out, or sometimes it would power on with no sound (relay clicks on, final
preamp and output stages are fine). Tapping the volume up or down control
causes it to come back on. Without a service manual, I could only take
guesses. I replaced two IC's (TC9177P and TC9185P, volume control) on the
control board, but no change. I replaced a third IC (AN4046 equiv) and again
no change. In desperation, I tried replacing every last transistor and
filter capacitor on that board, and checked the value of every last
resistor. STILL no change.
Never one to give up easily, I'm considering ordering a service manual.
But if there's a possibility of logic problems or other
expensive/tricky/impossible repairs needed, I don't want to waste $20 on a
manual. Do you think this is a simple problem or will it require too much
time and money to make it worthwhile? Or is it possible that the replacment
IC's were defective?
Thanks for any advice.

--
To reply via Email, remove NOSPAM from the address

I've got the same system and have had the same problem numerous times.
The slider volume control has been the culprit on mine. Once I gave it
a very vigorous cleaning it worked great for a while. Every once in a
while I've got to do it again. In fact it is starting to act up again
now so I guess I should dig into it. I ordered the service manual way
back when I first bought the system so if you have any questions about
any specific part I can give you the reference from the manual.

Cheers,
Lawrence

lmcclaf wrote:
I've got the same system and have had the same problem numerous times.
The slider volume control has been the culprit on mine. Once I gave it
a very vigorous cleaning it worked great for a while. Every once in a
while I've got to do it again. In fact it is starting to act up again
now so I guess I should dig into it. I ordered the service manual way
back when I first bought the system so if you have any questions about
any specific part I can give you the reference from the manual.

Cheers,
Lawrence

I was going to say... how about just cleaning the controls?

Mark Z.

No this doesn't have a slider pot.... just two pushbuttons which control the
IC's. The circuit is digital not analog, which is what makes it so hard to
work on. I can get free datasheets for the IC's, but I'm not exactly certain
what to look for.... I don't have much experience troubleshooting logic
circuits.

"Mark D. Zacharias" wrote in message
om...
lmcclaf wrote:
I've got the same system and have had the same problem numerous times.
The slider volume control has been the culprit on mine. Once I gave it
a very vigorous cleaning it worked great for a while. Every once in a
while I've got to do it again. In fact it is starting to act up again
now so I guess I should dig into it. I ordered the service manual way
back when I first bought the system so if you have any questions about
any specific part I can give you the reference from the manual.

Cheers,
Lawrence

I was going to say... how about just cleaning the controls?

Mark Z.

Oops sorry, my mistake. I misread the model number. My unit is a
CA-271.

Lawrence

Check the speaker relay-s . Have the thing going and when it quits stick
a screwdriver across the relay contact pins on the bottom of the board
or ``whack`` the relay .

Nope, not it. I would have found that quite easily. As I said in my first
post the main output stage is fine (you can inject a signal), the trouble
seems to be in the volume control section.
Maybe this thing just isn't worth bothering with.......

"Ken G." wrote in message
...
Check the speaker relay-s . Have the thing going and when it quits stick
a screwdriver across the relay contact pins on the bottom of the board
or ``whack`` the relay .

That TC1985P chip uses leg 3 as an inhibit or some such thing for when
you turn the system off to retain a memory of where the volume was set
or something like that. If you measure what you have at that leg when
things are fine and then measure again when it kicks out you might find
something funny being felt there which is throwing the volume out of
whack. Tapping the volume controls would then override what the
"memory" is trying to do so that might be why it is coming back when
you hit the buttons. Grasping at straws here but doesn't cost nothing
for a look.

Cheers,
Lawrence

"Chris F." wrote in news:AHeXg.4049$cz.58002
@ursa-nb00s0.nbnet.nb.ca:

the trouble seems to be in the volume control section.
Maybe this thing just isn't worth bothering with.......

CLEAN THE DANG VOLUME CONTROL!!!

It's DIGITAL NOT A SLIDER POT!!

"Jim Land" wrote in message
. 3.44...
"Chris F." wrote in news:AHeXg.4049$cz.58002
@ursa-nb00s0.nbnet.nb.ca:

the trouble seems to be in the volume control section.
Maybe this thing just isn't worth bothering with.......

CLEAN THE DANG VOLUME CONTROL!!!

It's DIGITAL NOT A SLIDER POT!!
yes and no. It's a cheapie control. Typically they're using conductive
and non conductive 'spokes' with rotary sliders running across them to
generate the digital signal, usually a quadrature square wave. If the
sliders or the conductive spokes get dirty/intermittent you get extra
glitches which will give you a screwed up count or no contact which will
give you no count at all, hence intermittent control or no volume.
An awful lot of all-in-one small stereo's suffer from this.
The bad news is the pot is probably sealed so good luck getting cleaner
into it.
And if it is a all-in-one small stereo good luck getting at the control!

tomh

"Jim Land" wrote in message
. 3.44...
"Chris F." wrote in news:AHeXg.4049$cz.58002
@ursa-nb00s0.nbnet.nb.ca:

the trouble seems to be in the volume control section.
Maybe this thing just isn't worth bothering with.......

CLEAN THE DANG VOLUME CONTROL!!!

Perhaps I should be more clear: there are two buttons - one for volume up,
and the other for volume down. There are no pots involved whatsoever, it is
entirely logic-controlled.

"tomh" wrote in message
...

It's DIGITAL NOT A SLIDER POT!!
yes and no. It's a cheapie control. Typically they're using conductive and
non conductive 'spokes' with rotary sliders running across them to
generate the digital signal, usually a quadrature square wave. If the
sliders or the conductive spokes get dirty/intermittent you get extra
glitches which will give you a screwed up count or no contact which will
give you no count at all, hence intermittent control or no volume.
An awful lot of all-in-one small stereo's suffer from this.
The bad news is the pot is probably sealed so good luck getting cleaner
into it.
And if it is a all-in-one small stereo good luck getting at the control!

tomh

"Jim Land" wrote in message
. 3.44...
"Chris F." wrote in
news:AHeXg.4049$cz.58002
@ursa-nb00s0.nbnet.nb.ca:

the trouble seems to be in the volume control section.
Maybe this thing just isn't worth bothering with.......

CLEAN THE DANG VOLUME CONTROL!!!

ahhh, excuse me, well check the buttons themselves, to see if they are
closing. Pulling up to +V or down to ground. In an older unit they'll
probably be directly connected to the chip doing the volume control. Or
to a chip that puts out a data stream to the volume control chip. If
it's a newer unit they may be scanned by a 'jungle chip', and you'll
need a scope to check the waveform at the switch. If tapping or wrapping
on the chassis brings the volume back or makes it go away, I'd also get
out the magnifier and look for bad solder joints and breaks. If it is a
newer unit with lots of IC's and you don't mind spending the time, do a
lot of resoldering around the volume control IC and elsewhere. Ya might
get lucky...

Perhaps I should be more clear: there are two buttons - one for volume up,
and the other for volume down. There are no pots involved whatsoever, it is
entirely logic-controlled.

"tomh" wrote in message
...
It's DIGITAL NOT A SLIDER POT!!
yes and no. It's a cheapie control. Typically they're using conductive and
non conductive 'spokes' with rotary sliders running across them to
generate the digital signal, usually a quadrature square wave. If the
sliders or the conductive spokes get dirty/intermittent you get extra
glitches which will give you a screwed up count or no contact which will
give you no count at all, hence intermittent control or no volume.
An awful lot of all-in-one small stereo's suffer from this.
The bad news is the pot is probably sealed so good luck getting cleaner
into it.
And if it is a all-in-one small stereo good luck getting at the control!

tomh
"Jim Land" wrote in message
. 3.44...
"Chris F." wrote in
news:AHeXg.4049$cz.58002
@ursa-nb00s0.nbnet.nb.ca:

the trouble seems to be in the volume control section.
Maybe this thing just isn't worth bothering with.......

CLEAN THE DANG VOLUME CONTROL!!!