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 Post subject: Any Pioneer experts? SX-1080 FM issues
PostPosted: May Thu 19, 2022 12:02 pm 
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Location: Dayton Ohio 45424
Working on this rec. for somebody. Uses the awful PA 1001 1002 3001 chips. At first the audio was garbled, no meter, no mute. Replaced bad PA3001 IF/Det. with the Hitachi equivalent. Restored meter, mute, and clean 550 mV sine to the 1001 MPX chip with 30 KHz deviation. Output of the L and R of the 1001 is down in the noise. With an OTA stereo signal, there are huge 3.7V 38 KHz tilted square waves on the L R outputs of the chip. Of course that goes thru a LPF to the audio amp chip. There is recovered stereo sound from the tuner but the audio level is a great deal lower than AM. Even with 1 mV RF from the test gen. But the tuner is super sensetive in the RF stages. I am thinking the MPX chip may be bad too with such tiny recovered audio. But the audio chip has it's own issues. An apparent 2 MHz oscillation that appears at the output at about 50mV Peak at all times except when the inputs were disconnected. Anyone have a Pioneer that they would consider taking a few measurements on with this chip set? BTW I do not have MPX in my RF gen, just FM selectable dev.

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 Post subject: Re: Any Pioneer experts? SX-1080 FM issues
PostPosted: Jun Sat 11, 2022 5:42 am 
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Typically that problem was caused by bad coupling or 'lytic caps. Been 40 yrs or so since I worked on one of those.

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 Post subject: Re: Any Pioneer experts? SX-1080 FM issues
PostPosted: Jun Sat 11, 2022 11:31 am 
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I'd replace the caps, which btw I don't necessarily suspect. But they are a lot easier to get than the chips, which is most likely the problem. They are notorious, and getting extremely hard to find. You may get lucky and a few caps will fix it. I'm not betting on that ;-)

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 Post subject: Re: Any Pioneer experts? SX-1080 FM issues
PostPosted: Jun Tue 14, 2022 12:51 am 
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Did extensive cap testing in the problem areas. I sent it back to the owner telling him to take it to one of the pro shops in the region that have or should have MPX generators for one thing.

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