Problem with AKAI AC510 stereo

[Jean-Marc Delaplace]

Hi,
my set has a curious behavior: when the antenna signal lowers, the sound
is chopped at the pace of the music, i.e. when the music is smooth,
the sound is ok, but when the music has attacks, the sound cuts a
fraction of a second a each attack. I suspect some electrolytic
capacitor to be dry, but which one? Does anyone have the schematic of
this set?
Thanks in advance.
Jean-Marc

 

[Arfa Daily]

"Jean-Marc Delaplace" <jeanmarc.delaplace@free.fr> wrote in message
news:49226781$0$8482$426a74cc@news.free.fr...

Hi,
my set has a curious behavior: when the antenna signal lowers, the sound
is chopped at the pace of the music, i.e. when the music is smooth, the
sound is ok, but when the music has attacks, the sound cuts a fraction of
a second a each attack. I suspect some electrolytic capacitor to be dry,
but which one? Does anyone have the schematic of this set?
Thanks in advance.
Jean-Marc

Have you tried forcing the tuner to 'mono' mode to see if the problem still
occurs ? It might be just that you are seeing 'normal' behaviour from the
stereo decoder circuitry, when the signal is marginal. If the tuner section
is of the older more traditional design, then if it is happening in stereo
mode only, you might want to try adjusting either of pilot tone PLL pot or
the discriminator coil.

Arfa

 

[Mark D. Zacharias]

"Jean-Marc Delaplace" <jeanmarc.delaplace@free.fr> wrote in message
news:49226781$0$8482$426a74cc@news.free.fr...

Hi,
my set has a curious behavior: when the antenna signal lowers, the sound
is chopped at the pace of the music, i.e. when the music is smooth, the
sound is ok, but when the music has attacks, the sound cuts a fraction of
a second a each attack. I suspect some electrolytic capacitor to be dry,
but which one? Does anyone have the schematic of this set?
Thanks in advance.
Jean-Marc

I have seen older tuners do this sort of thing. Alignments generally fix
them. It may be switching stereo-mono or the mute circuit may be triggering
on peaks. My Onkyo T-4055 did that. I had adjusted the muting threshold
where I liked it instead of the specification. Had to re-do it for the
muting problem. Interestingly, it worked fine in the shop using a generator
and a sine wave input. I had to externally modulate the generator with drum
samples to re-create the problem in my shop.

Mark Z.

 

[Meat Plow]

On Tue, 18 Nov 2008 09:50:52 -0000, "Arfa Daily"
<arfa.daily@ntlworld.com>wrote:

"Jean-Marc Delaplace" <jeanmarc.delaplace@free.fr> wrote in message
news:49226781$0$8482$426a74cc@news.free.fr...
Hi,
my set has a curious behavior: when the antenna signal lowers, the sound
is chopped at the pace of the music, i.e. when the music is smooth, the
sound is ok, but when the music has attacks, the sound cuts a fraction of
a second a each attack. I suspect some electrolytic capacitor to be dry,
but which one? Does anyone have the schematic of this set?
Thanks in advance.
Jean-Marc

Have you tried forcing the tuner to 'mono' mode to see if the problem still
occurs ? It might be just that you are seeing 'normal' behaviour from the
stereo decoder circuitry, when the signal is marginal. If the tuner section
is of the older more traditional design, then if it is happening in stereo
mode only, you might want to try adjusting either of pilot tone PLL pot or
the discriminator coil.

Arfa

I'd agree it needs tweaked. Appears by description the circuit may be
switching from mono to stereo and muting the transitions. I'm sure
I've come across this, sounds familiar amongst the myriads of Akai
receivers on my bench at the factory authorized repair center.

 

[Dave Platt]

my set has a curious behavior: when the antenna signal lowers, the sound
is chopped at the pace of the music, i.e. when the music is smooth, the
sound is ok, but when the music has attacks, the sound cuts a fraction of
a second a each attack. I suspect some electrolytic capacitor to be dry,
but which one? Does anyone have the schematic of this set?
Thanks in advance.
Jean-Marc

I have seen older tuners do this sort of thing. Alignments generally fix
them. It may be switching stereo-mono or the mute circuit may be triggering
on peaks. My Onkyo T-4055 did that. I had adjusted the muting threshold
where I liked it instead of the specification. Had to re-do it for the
muting problem. Interestingly, it worked fine in the shop using a generator
and a sine wave input. I had to externally modulate the generator with drum
samples to re-create the problem in my shop.

I wonder if that might indicate that on peaks, the FM signal is
modulated so strongly that it's deviating outside of the IF's
passband?

In communications receivers (e.g. ham and commercial) this causes a
problem called "talk-off" - if you speak too loudly, the receiver
mutes on the peaks. If the signal deviates out past the edges of the
IF passband, the effective signal level coming in to the limiter drops
and the noise level comes up, and the resulting brief burst of
high-frequency noise triggers the muting.

Misalignment of the IF, or of the quadrature decoder could cause this.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Jean-Marc Delaplace]

Thanks to everybody for these opinions.
JMD


Dave Platt a écrit :

my set has a curious behavior: when the antenna signal lowers, the sound
is chopped at the pace of the music, i.e. when the music is smooth, the
sound is ok, but when the music has attacks, the sound cuts a fraction of
a second a each attack. I suspect some electrolytic capacitor to be dry,
but which one? Does anyone have the schematic of this set?
Thanks in advance.
Jean-Marc

I have seen older tuners do this sort of thing. Alignments generally fix
them. It may be switching stereo-mono or the mute circuit may be triggering
on peaks. My Onkyo T-4055 did that. I had adjusted the muting threshold
where I liked it instead of the specification. Had to re-do it for the
muting problem. Interestingly, it worked fine in the shop using a generator
and a sine wave input. I had to externally modulate the generator with drum
samples to re-create the problem in my shop.

I wonder if that might indicate that on peaks, the FM signal is
modulated so strongly that it's deviating outside of the IF's
passband?

In communications receivers (e.g. ham and commercial) this causes a
problem called "talk-off" - if you speak too loudly, the receiver
mutes on the peaks. If the signal deviates out past the edges of the
IF passband, the effective signal level coming in to the limiter drops
and the noise level comes up, and the resulting brief burst of
high-frequency noise triggers the muting.

Misalignment of the IF, or of the quadrature decoder could cause this.