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SX 450 No AM/FM

This corrected schematic may be useful:

http://www.wwdsltd.com/files/PioneerSX-450Schematic.jpg

PioneerSX-450Schematic.jpg
 
I'm not certain that "expertise" is the appropriate term. I have shuffled into some San-Sushis, yanked around Yama-Mas, fooled with Fishers, krashed some Kenwoods, muddled through some Macs, toyed with Technics, Teac, and Toshiba, bumbled through Brooks, and played with Panasonics, but I cut my teeth on Pine-Ears. It is much like appreciation for the mechanic who can make a Ferrari run better than Enzo ever imagined, or one who understands the subtle nuances of an Alfa Romeo, everyone who opens the hood of a Chevrolet can understand what's going on.

In our realm, everyone can operate a Tektronix 'scope, but some of the more obscure brands can be confusing. Everyone can figure out the scales and ranges on a Fluke, but the "Bang-Ma-Wang" knock-offs can even befuddle an engineer. Everyone knows what end of the toilet paper to grab, even if the roll is sideways. And almost everyone can understand Pioneer. When you're the most prolific, produced, universal product on the market, the concepts pretty much set the standard which everyone holds as a base level of how things should be done.

Whenever I get confused (which is frequent) I can pull out an equivalent circuit from a Pioneer and the scheme can become clearer. Then, like an algebraic equation, I apply the concept to whatever unit which was about to be swept off the bench and into the scrap bin, and things can make more sense.
 
I'm back to this SX 450 after a major medical issue. Let's just say I'm glad to be here so I'm able to work on this unit again.

I still have no sound or AM/FM deflection meter action on this receiver in AM/FM mode. AUX, Phono, Tape - Rec/Play all work as normal.

Here's my question; Which way would be better/easier to use so I can check the tuner function?

1. I acquired another working receiver (Sony STR-7025) with a good AM/FM tuner that can be hooked up to the SX 450 ( I don't know how to do this).
OR
2. I have a spare AWE-074 board without the selector switch. This was an eBay purchase that's supposed to be in working order. Could I connect only the tuner and power test points to see if this fixes the tuner problem?

Any suggestions/recommendations would be much appreciated.

Thanks,
Mike
 
Put the SONY right next to the Pioneer. Tune 90.0mHz on the Sony and turn on. Turn on the Pioneer, and tune to 100.7mHz. (10.7mHz RF intermediate Frequency differential) if the RF Section (Local oscillator) on the Pioneer is working you should hear a decreasing pitch close to 100.7 with it going NULL and then increasing on the other sideof center freq. Do the same with AM radio only use 600kHz on the good radio and tune to 1055kHz or so (455kHz AM intermediate frequency differential). AM may be really hashy.
 
FM and AM tuner front ends share a common power source, what I was looking for on the diagram. Check voltage on that line @ both ends of the 2.2 uH choke coil.
 
larryderouin said:
Put the SONY right next to the Pioneer. Tune 90.0mHz on the Sony and turn on. Turn on the Pioneer, and tune to 100.7mHz. (10.7mHz RF intermediate Frequency differential) if the RF Section (Local oscillator) on the Pioneer is working you should hear a decreasing pitch close to 100.7 with it going NULL and then increasing on the other sideof center freq. Do the same with AM radio only use 600kHz on the good radio and tune to 1055kHz or so (455kHz AM intermediate frequency differential). AM may be really hashy.
Click to expand...
I put the Sony next to the Pioneer and did the AM test first. Sony/Pioneer was set to 600kHz/1055kHz, respectively. I tuned around 1055kHz on the Pioneeer and got no pitch sound.

I did the FM test next. Sony/Pioneer was set to 90.0mHz/100.7mHz, respectively. I got no sound when tuning around 100.7 mHz on the Pioneer.

I hope I did this test correctly. Thanks Larry for your assistance.
 

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micrometer said:
What should the voltage be at L102?

I'll start checking components upstream from L102. Thanks Pio1980.
Click to expand...
Ca 13,7 VDC, sourced thru the function switch S3 deck 2/2 F(front), as I suspected. Follow lead and look there, being careful not to short circuit anything with probes.
 
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Also, check fuse FU2 and regulator ckt around Q302 as the 13.7 VDC source if no joy @ the function switch.
FU2 first as the simplest check.
 
Pio1980 said:
Also, check fuse FU2 and regulator ckt around Q302 as the 13.7 VDC source if no joy @ the function switch.
FU2 first as the simplest check.
Click to expand...
FU2 shows continuity as well as all other five fuses.

When I pulled and checked all Q's on the AWE-074 board, Q104 was open. I pulled the Q104 from my spare board and it was good. I swapped it.
 
Pin 20 on the RF Assy bd is the main B+ for the tuner. Check for 13.7Vdc there. Follow it downstream to
a.) H1156 Pin4, Pin 5 (Both 11.2v), Pin 1(13.7V)
b.) Q105 & 106 Emitters (no voltage given) These are 2sa725's known troublemakers. replace with KSA992's.
c.) Selector (S3) Wafer 2 Front pin 2 (13.7V). With Selector in AM Check pin 3 for same voltage, then Pin 2 HA1137 (1.9V). In FM Check pin 11. Should be 13.7v. if not check for dirty contacts on wafer or burnt/lifted contact arm. Lift one side of L102 (or remove from circuit) and check voltage at pin 11 again. If 13.7 now,problem lies in area downwind of L102. If still low, follow schematic to Pin 14 on HA1156W. Check pin 14 voltage.
d.) Pin11 on HA1137. Should be 12v.
 
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