SX-1010 right channel dead on FM stereo

brainbanger

brainbanger

Member
Hi guys,

protection board issue fixed, next problem showing up: the right channel is dead on FM Stereo only, Mono and all other sources work ok.

Measured FM Output on Pins 17 + 19 on the Tuner Assy AWE-040 with a scope. While tuned to a stero FM Station (stereo indicator on), Pin 19 (left out) delivers a signal, Pin 17 (right out) is dead.
Checked & compared Q9 and Q10, as well as Q7 and Q8. All voltage readings match the SM. Also, IC HA1156 matches all readings against SM.

I am stuck because my limited knowledge is not sufficient to identify the signal path on the board to track the error down. Anyone able to help me? Eyes, ears, DMM, scope and an open minded "50+" brain available :D

Regards,
Andreas
 
Last edited:
brainbanger said:
Hi guys,

protection board issue fixed, next problem showing up: the right channel is dead on FM Stereo only, Mono and all other sources work ok.

Measured FM Output on Pins 17 + 19 on the Tuner Assy AWE-040 with a scope. While tuned to a stero FM Station (stereo indicator on), Pin 19 (left out) delivers a signal, Pin 17 (right out) is dead.
Checked & compared Q9 and Q10, as well as Q7 and Q8. All voltage readings match the SM. Also, IC HA1156 matches all readings against SM.

I am stuck because my limited knowledge is not sufficient to identify the signal path on the board to track the error down. Anyone able to help me? Eyes, ears, DMM, scope and an open minded "50+" brain available :D

Regards,
Andreas
Click to expand...

Try pushing the FM selector switch in a little past where it sits. Wiggle it a little, if you can get some sound out it's probably what rlovison stated.

I would fidget with the FM selector switch.. :)

Good Luck!
 
I know that it is not related to any of the switches. Did a full recap on all boards, desoldered, disassembled (where possible) the switches, cleaned / de-oxited, lubed and resoldered every one of them, followed by thorough testing - they work like new. :yes:
 
brainbanger said:
I know that it is not related to any of the switches. Did a full recap on all boards, desoldered, disassembled (where possible) the switches, cleaned / de-oxited, lubed and resoldered every one of them, followed by thorough testing - they work like new. :yes:
Click to expand...

Check your solder joints for a good connection, and all wiring for shorts, or loose wires. Kind of an odd situation. The issue only occurs when the FM is selected...? Did the right channel work at all when the recap was done?

Could be a film resistor on the tuner board... I was working on a Sansui Au717 and one issue was the right channel not working with the AUX, turns out it was a metal film resistor on the phono board... The aux runs threw the tuner on the 717..

Check the SM, see if there are any film resistors on the tuner board..

would not be a cap, a transistor would have more issues, but not limited...

Humm I'm interested to know what this is..

Good Luck,
John
 
It is only FM, all other sources work well. I cannot tell if it ever worked, as the unit came in dirty and messed up. Reworked it to working condition, but the missing right channel in FM prevents me from finishing it up.

The tuner board is hard to work on. It is nearly impossible to reach the foil / solder side without damaging the wire-wraps :thumbsdn: So I guess the best option is to track the right channel signal on the component side first. When something is found that requires soldering on the backside: :tears:
 
Just to be clear: Stereo/Mono switch in stereo position, the right channel drops when the Stereo light comes on? In all other cases you have signal on the right channel?
 
Signal goes thru ALL of the flip switches (Tape monitors, Duplicate, Hi and Low Filters, etc., plus the tone controls, Balance and volume. Mono Sums the Left and Right Channel signals, so if you lose 1 channel in STEREO, you'll have 2 channel in MONO(Note that I didn't say stereo). I'd be more inclined to go thru all of the switches, pots, etc. again.

Take a RCA Cable and solder a .1uf/400 cap to the center tap. Plug other end into another amp/receiver. Use this as a signal tracer. Work back thru the amp board/tone control board, all the switches, all the way back to the FM output on the tuner. (or use an o-scope doing the same thing.)
 
I don't have any signal on pin 17 of the tuner board (right channel out), pin 19 (left) is fine, so the oscilloscope doesn't lie.

I assume that switches won't matter, as they are further down the signal path?

Do I need the probe when I have the oscilloscope?
 
Nope. Use the scope to trace back from pin 17 thru F-5 (low pass filter) back to pin 5 on Q5(HA-1156). Also check output on pin 22.
 
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oh great, 4 transistors, 2.2uf cea caps (c28 and c29) and an atf-019 lo pass filter -

all from above...

identify resistor leads and probe them.

hate to say it, but the F5 lo pass filter is the most likely suspect as long as q7 and q8 are not 2sa725/2sa726's...

if they are use ksa992's for q7, q8, and if q9, q10 2sc945's are bad, ksc1845.
 
Ah ok, it wasn't clear that you never had signal at pin 17. In that case, larryderouin's advice should quickly track down the problem.
 
Bingo!

Pin 22 was alive, so there IS a right channel somewhere...

Measured transistors, all good against SM:
Q7: 2sa763: B=+9.7 C=+5.2 E=+9.1
Q8: 2sa763: B=+9.7 C=+5.2 E=+9.1
Q9: 2sc945: B=+2.2 C=+7.3 E=+1.6
Q10: 2sc945: B=+2.2 C=+7.3 E=+1.6

Traced back from Pin 17 and suspected C30 (little blue Panasonic), as I could measure something at positive (Q9 collector), but nothing on negative (Pin 17) side. Desoldered C30 (tricky), but it measured ok?!? Put it back in and started probing the resistors:
R42 (220K) is the winner of the SX-1010 Tuner "Open"! (and yes, it was...). Replaced it and enjoy full FM stereo now. :music:

Thanks to all that helped with hints and tipps, much appreciated!

Happy Easter from Germany,
Andreas
 
Last edited:
brainbanger said:
Bingo!

Pin 22 was alive, so there IS a right channel somewhere...

Measured transistors, all good against SM:
Q7: 2sa763: B=+9.7 C=+5.2 E=+9.1
Q8: 2sa763: B=+9.7 C=+5.2 E=+9.1
Q9: 2sc945: B=+2.2 C=+7.3 E=+1.6
Q10: 2sc945: B=+2.2 C=+7.3 E=+1.6

Traced back from Pin 17 and suspected C30 (little blue Panasonic), as I could measure something at positive (Q9 collector), but nothing on negative (Pin 17) side. Desoldered C30 (tricky), but it measured ok?!? Put it back in and started probing the resistors:
R42 (220K) is the winner of the SX-1010 Tuner "Open"! (and yes, it was...). Replaced it and enjoy full FM stereo now. :music:

Thanks to all that helped with hints and tipps, much appreciated!

Happy Easter from Germany,
Andreas
Click to expand...

Great thread!!! Happy Easter as well from CA!!! Glad you got it going!
 
A 220k ohm resistor failed... hmmm.... we don't see a lot of that, in fact it's very rare! Congratulations on the save!!
 
Brain; Congrats on the save. Hopefully it'll last a LOOOONNNNNNGGGGGG Time.

Larry
 
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