Pioneer SX-980 problem - no relay click

[Joakim Skoog]

Hi,
I have a Pioneer SX-980 in nice condition which have not been used for many years.
When I started t up it worked for some hours but then the relay click was not there and no sound from the speakers. I have downloaded the service manual and read many threads on this forum how to trouble shoot.

This is my measures from the power supply board AWR-165
Pin 16 +13VDC 13.0
Pin 17 +13VDC 13.0
Pin 18 +7.5VDC 12.6
Pin 19 +65VDC 79.2
Pin 20 +33VDC 34.9
Pin 21 GRND 0
Pin 22 +50VDC 51.9
Pin 23 +23VDC 24.0
Pin 24 +24VDC 24.0
Pin 25 -23VDC 0.7
Pin 26 -23VDC 0.7
Pin 27 -50VDC 1.1
Pin 28 -13VDC 0.6

No negative voltages. Should I have those even if the relay don't click?

I would really appreciate any kind of help.
Thanks

 

[Watthour]

Yes, the -50V supply should be present regardless of whether the protection relay is on or off. Are the ±65V supplies present at the filter caps?

 

[Joakim Skoog]

I hope I understand you correctly. Do you mean voltage at pin 19 and the connection between R7 and R8 on the power supply board?
If that is the case they are 79.2 respectively -82.2

 

[Watthour]

You understood correctly. The junction of R7/R8 should be the -65V bus, and Pin 19 is the +65V bus. Your AWR-165 is slightly different than what I have in my schematics (AWR-164) but the rail voltages should be close.

The important point is that there is -82V present. I would take a close look at Q4, Q3, the zeners, and the surrounding resistors. That array should be producing around -50V at Pin 27 any time the unit is powered on, and without regard to the protection circuit.

 

[Joakim Skoog]

I measured the Q3 and Q4
Q3 B=0.3V (-13.6) E=0.6V (-13) C=-83.3V (-50.6)
Q4 B=-83.3V (-50.6) E=1.4V (-50) C=-83.8V

I guess both show strange values and I plan to replace them. Is there a way of checking the zener diod without removing them?

 

[Watthour]

The 83V seems a bit high. If you have a multi-voltage plug it might be good to check its setting. It sounds as it it might be on a 110V tap operating on 120V, or on a 220V tap operating on 240V.

Regarding the zener, it would be best to desolder and lift one end when you are in there changing transistors. Thus, for the minimal cost of a replacement 13V zener, you may want to get a couple of those when you get replacement transistors. While you are in the circuit replacing transistors, desolder one leg of the zener and test it. If it reads normally, reinstall it. If not, you'll have replacements at hand. A good substitute for the MZ-130 might be one of THESE.

 

[Joakim Skoog]

Thanks for the reply. It is actually set to 220 but operating at 230V. I try to set it at 240v and got +33.1 resp -74.9 at the filter caps and 51.4V on pin 22. Any idea what to prefer? Set it to 220 or 240V?