Pioneer SX-3700 Relay does not Engage when Am or FM is Engaged at Power On

[AndyCares]

Hoping someone can lend some advice. Picked up an SX-3700. When either AM or FM is engaged during power on, the relay does not turn over. If I switch the input to either of the remaining (AUX/Phono), the relay engages and stays engaged when switching back to FM or AM. One more detail: relay does nothing when on FM at power up, but if AM is engaged during power up, the relay makes a noise like it wants to engage for 5-10 seconds, then nothing until I go over to one of the other two channels. I cleaned all switches and knobs w DeOx, etc. Haven't really done much else. Hoping someone can point me in the right direction.

Thanks!

Andy

 

[Robisme]

Sounds like the tuner is dragging down the voltage needed to fire the relay. Check the voltage across the relay coil when powering up with FM selected, then with AUX selected.



Rob

 

[AndyCares]

Sounds like the tuner is dragging down the voltage needed to fire the relay. Check the voltage across the relay coil when powering up with FM selected, then with AUX selected.



Rob

Thank for the replay! I'm not sure if there is a secret to getting a reply bc I seem to have a hard time gaining any interaction. Anyway thank you and I will check this out tonight and report results!

 

[Robisme]

You could also check the output of the tuner for DC voltage on power up. Pin 44 to ground and 45 to ground for FM and 43 to ground for AM.

If DC on pins 44,45 it could be capacitor C40 or C41.

This is a very strange problem.

Rob

 

[AndyCares]

You could also check the output of the tuner for DC voltage on power up. Pin 44 to ground and 45 to ground for FM and 43 to ground for AM.

If DC on pins 44,45 it could be capacitor C40 or C41.

This is a very strange problem.

Rob

Here's the results I found:
Tuner:
Pins 44 & 45: Jumps all over the place when on FM/cannot get a solid reading
Pin 43: 12.42v on AM
*This is after I switch to a non-radio input (aux/phono) and back. Upon power up before the relay engages from the aforementioned 'switch,' there is barely a reading (~0.002-0.004)

Protection:
Pin 46: 0.021
Pin 47: 0.018
Pin 48: -0.048
Pin 49: -0.044

Thanks again! Will maybe pull C40-41 and see how they test out of circuit.

 

[AndyCares]

You could also check the output of the tuner for DC voltage on power up. Pin 44 to ground and 45 to ground for FM and 43 to ground for AM.

If DC on pins 44,45 it could be capacitor C40 or C41.

This is a very strange problem.

Rob

C40, 41 tested fine. While I was in there, I replaced most caps in the signal path with films. Tough amp to work on - you have to remove the 'upper mezzanine' in order to access half the tuner, protection, etc. No luck yet. If the readings I shared indicate anything, let me know. Appreciate the insight

 

[AndyCares]

Here's the results I found:
Tuner:
Pins 44 & 45: Jumps all over the place when on FM/cannot get a solid reading
Pin 43: 12.42v on AM
*This is after I switch to a non-radio input (aux/phono) and back. Upon power up before the relay engages from the aforementioned 'switch,' there is barely a reading (~0.002-0.004)

Protection:
Pin 46: 0.021
Pin 47: 0.018
Pin 48: -0.048
Pin 49: -0.044

Thanks again! Will maybe pull C40-41 and see how they test out of circuit.

I goofed on the pins 46-49. This was idle current and both channels tested fine around 4mV each..

 

[AndyCares]

You could also check the output of the tuner for DC voltage on power up. Pin 44 to ground and 45 to ground for FM and 43 to ground for AM.

If DC on pins 44,45 it could be capacitor C40 or C41.

This is a very strange problem.

Rob

Update: I replaced 2 capacitors C115, 116 right next to the relay (as well as Q25 (KSC2690) and had some luck! Once I swapped the caps, The relay began to engage when powering on with AM/FM selected, albeit pretty slow - maybe 6-8 seconds after power up. After testing this a few times, the relay stopped engaging when FM was selevcted, but still engaged when AM was selected on power up. That said, now when FM was selected on power up, the relay would buzz (fight to engage) and would engage with a small flick on the relay. So I obviously made some progress, but don't know where to go from here. Seems FM is still drawing too much power, but replacing those caps (namely c116, 47/50) definitely made a difference. Any ideas would be much appreciated! Trying to locate the timing caps, but I know this won't solve the entire issue - maybe once the FM is solved, I could lower the value to lessen the time it takes for the relay to engage on power up..