Pioneer SX-950 receiver

[Tomcow]

Hello Anyone have or know what the pin readings on the protection board of this receiver should be?Trying to trace down a problem and the schematic I have is hard to read.Thanks.

 

[Tom B]

Check that power supply board good. Because of its potition underneath it really cooks, and I have found failures, with the DC supplies from bad transistors, and overheated connections

 

[Tomcow]

I am having the weirdest problem. The relay clicks on,But I am getting rail voltages on my speaker outputs.All eight output transistors test good I can’t find any problems on the power supply board, i’ve never had a receiver I repaired click on So-cleanly,And have 40+ Voltages DC in both right and left channels!

 

[Tomcow]

I’m Pretty sure there’s a problem with the protection board. All the diode’s zenor diode’s,All test good with the power off. When the receiver is powered on, five of those diode‘s read overload.

 

[Tomcow]

I have all the voltages for the power supply pins, the output boards,And the protection really boards if that would help anyone help me figure this out.

 

[Tom B]

The protection board will noth cause 40Vdc on the speaker outs. Thats usually power supply or issues with the power amp. I would think you could be missing the +51v, or the -51v, or the plus 36v, from the regulator board going to your power amp board. There is also plus 49v, and - 49v are unregulated, and go to the output transistors as well.

 

[Tomcow]

The regulator board is which board?As I stated,I have all the voltage readings off the power supply board,Right and left amp output boards and the protection board if that would help.

 

[Tom B]

The regulator board is which board?As I stated,I have all the voltage readings off the power supply board,Right and left amp output boards and the protection board if that would help.

power supply board AWR-101 has the regulator supplies
protection board is AWM-062.
power amp board is AWH-050

The collector (case ) of the NPN outputs (2SD427) should read 49v dc
The collector (case ) of the PNP outputs (2SB557) should read -49vdc

On the power amp board the voltage reading should be
pin 7 and pin 9 should be 51.5v
pin 4 and pin 5 should be 36.5v
pin 6 should read 0v as a ground connection
pin 2 should read -51.5v (and probably pin 1)
pin 22 and pin 23 should read 51.5v
pin 19 and pin 20 should read 36.5v
pin 21 should read 0v as a ground connection
pin 16 and pin 17 should read -51.5 v

All of these voltage points originate from the regulator power supply board

Also you should read on this board
pin 14 and pin 23 (or 29) as 49.5v
pin 10 and pin 11 (close to 0v dc as these are the left output of the amp)
pin 12 and pin 13 (close to 0v as these are the left channel feeds to the protect board)
pin 9 and pin 24 0v (chassis ground)
pin 15 and pin 30 should be -49.5v
pin 25 and pin 26 (close to 0v dc as these are the right output of the amp)
pin 27 and pin 28 (close to 0v as these are the right channel feeds to the protect board)

 

[Tomcow]

Thank you I will check all those pins and post them

 

[Tomcow]

Amp output boards:1,-52.5V,2,-52.5V,3,-2.5V,4,36V,5,36V,6,0V,7,50V,8,50V,9,0V,10,-50V11,-50V,12,-50V,13,-50V,14,plus42V,15,-50.5,16,-52V,17,-52V,18,0V,19,36V,20,36V,21,0V,22,50V,23,50V,24,0V,25,26,27,28and 29 are all 42V,30,-51V

 

[Tomcow]

Power supply:1,0V,2 and 3,5.2V,4 and 5 are:13.5V,6 and 7 are:50V.8,9 and 10 are:36V.pin 11 is:28V.12 is 0V.pin 13 is:-13V. 14 is:-52.5V and pin 15 is:-19V

 

[Tomcow]

Protection board, Pin one is -50 V, pin two is-13.7 V. Pin three is +42 V, pin four is 0 V, pins five and six are -50.5 V, pin seven and 8+42 V, pins 910 and 11 R +36 V,Pin 12 is 7.2 V AC

 

[Tomcow]

I checked all eight output transistors, case to ground, between:43 and 49V on all of them on a 100W bulb dimmer.I am getting a relay on click, and then 1 to 2 seconds later another click which is probably protection.

 

[Watthour]

Summarizing:

Amp output boards:
1 -52.5V
2 -52.5V
3 -2.5V
4 36V
5 36V
6 0V
7 50V
8 50V
9 0V
10 -50V
11 -50V
12 -50V
13 -50V
14 42V
15 -50.5
16 -52V
17 -52V
18 0V
19 36V
20 36V
21 0V
22 50V
23 50V
24 0V
25 42V
26 42V
27 42V
28 42V
29 42V
30 -51V

Power supply:
1 0V
2 5.2V
3 5.2V
3 5.2V
4 13.5V
5 13.5V
6 50V.
7 50V.
8 36V.
9 36V.
10 36V.
11 28V.
12 0V.
13 -13V.
14 -52.5V
15 -19V

Protection board
1 -50 V
2 -13.7 V
3 42 V
4 0V
5 -50.5 V
6 -50.5 V
7 42 V
8 42 V
9 36 V
10 36 V
11 36 V
12 7.2 V AC

 

[Tomcow]

Yes.You have an extra 3 stated on the power supply listing.

 

[Watthour]

Protection board
1 -50 V (speaker output excessive)
2 -13.7 V
3 42 V (speaker output excessive)
4 0 V
5 -50.5 V
6 -50.5 V
7 42 V
8 42 V
9 36 V (O.K. with relay off)
10 36 V
11 36 V
12 7.2 V AC

The presence of more than a few millivolts at Pins 5, 6, 7, and 8 indicate an output transistor on or biased extremely high.

 

[Watthour]

Yes, I happen to like 3.


That said, all the power supply voltages appear to be nominal for operation on a 100W dim bulb at zero power output.

 

[Tomcow]

Looks like there is some trouble on:10,11,12,13 on the amp output board,along with pins 25 and 26.Indicates maybe the problem is on amp output board??

 

[Watthour]

It appears that the protection board is functioning properly.

I would suggest the output transistors be removed, and Q9. 10, 11, and 12 on the power amp be checked closely.

 

[Tomcow]

Okay.I have removed all eight output transistors and tested them individually.They we’re all good.So are you thinking the predrivers,D-381 and B-536,as well as A-818 and C-1628?