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 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.
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.
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.
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Dave Platt AE6EO
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Thanks to everybody for these opinions. JMD
Dave Platt a écrit :
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