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Pioneer SX-650 Woes

49hawkeye

49hawkeye

Member
Hi All,
New to the forum and have run into an issue I need some help on. First I'm not much on electronics diagnosis and have never tackled a job of this magnitude before so please bear with me. Additionally schematics are kind of foreign to me but I'm trying. Tried finding information before posting about this but came up empty.
Picked up the amp at an estate sale. Powers up fine but relay doesn't engage. I went ahead and replaced the caps, a few transistors and the relay on the 2 power amp boards and still dead. Started checking pins and all the 35V and -35V read fine. the others not so much. The power/speaker select switch seems to operate with no resistance measured in the on position.so don't think that's a problem. I started checking the power board and the 35V and -35V pins, 5 and 6 registered a bit over 37V. Pin 13 has 0 volts instead of -50 and pin14 has 0 volts instead of 48V. The 2 green wires from the transformer read -0.3V. Fuses are good. At this point I am assuming the transformer is bad but is there something else I need to look at?
Thanks for any assistance you can lend.
 
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What are the DC voltage readings at the emitter resistors? Anything more than a volt or less, and the relay won't close.
 
First thing is to get the power supplies working.
No -50v and 48v needs to be fixed. You have ohmed out the fuses numbered Fu2 and Fu3?

Measure ac volts going into the full wave bridge rectifier best if you can right at the diodes but ok from the output of the fuses.
Two possibilities either you have ac going into the rectifier or you do not.
If AC is present then bridge rectifier is bad
if NO AC fuses wiring or Transformer is bad.
 
Thanks for the reply. Please tell me where these resistors are and how many. I know that may sound a bit dumb but still trying to figure out all this.
 
What resistors are you talking about?
Measure AC volts one lead on Pin 1 and one lead on Pin 2 of Power Supply Assy AWR-117 This is the input from the transformer
Measure AC volts one lead on Fuse 2 and one lead on Fuse 3. this is the ac going to the full wave bridge rectifier google the term and understand what is happening here.

The components that make up the bridge are D1 - D4
 
Measure ohms on the power supply board (power off of course) from pin 8 to pin 11

I reread you pos and it seems you have already confirmed no ac voltage on pins 1 to 2 correct?
 
I was a little snoozy when I read the OP. I totally overlooked the part about the power supply not functioning. :whip:
 
Thanks for the information. Well, Remember I'm not very experienced. I had no idea pins 1 & 2 were AC voltage.
I pulled the fuses, turned it on and checked voltage again on AC this time. 50.3 and 50.4V. Cleaned the contact clips and replaced the fuses, turned it on and blew both. I missed the bad fuses before or at least didn't recheck them like I should.
I checked ohm readings from pin 14(5.45 m Ohms) to pin 26 (same) to pin K(4 m Ohms) and from pin 13(2.38 m Ohms) to pin 23(same) to pin N(3.34 m Ohms). So I guess now I'm looking for a short to ground or did I miss something? Where and how to start that process? I have a round trip of about 30 miles for fuses so should I buy a case?
Thanks again.
 
I decided to unsolder the wires going to GWR-101 at N and K. Since pins 23 and 26 on GWH-101 are just way points that separates all 3 boards. Once the wires were loose there is no grounding on the wires or the power board AWR-117 so the short is on GWR-101. I had installed new caps on C-21 thru 31 and C-33, 34, 35, 37 and 38 making sure polarity was the same as the old ones. None of the old ones had any visual damage. So where/what should I start checking? Are there any likely suspects on that board? One other thing - the grounding on the board increased to 10-15 m Ohms at the wire points.
Thanks for all the help so far.
Dave
 
Were the voltage ratings on the replacement caps the same or higher than the originals? It would certainly seem that C34/35 and C37/38 are prime suspects, and should be increased to a minimum 63V rating. Similarly, C24/25 should be bumped to at least a 50V rating. Other potential suspects are QA29/30 and the zeners D10/11.
 
Thanks Watthour,
Yes, 34, 35, 37 & 38 are 63V. 24 & 25 are 50V as are 31, 34 &35. Do I need to pull D10 & 11 to test and how are they tested? And sorry to sound even more stupid but what are QA29/30? You by chance live in the Quad Cities?
 
Sorry, that was my fat-fingering. It should have been C29/30.

"By" the Quad Cities is relative. It takes me almost 2 hours to get there, and I have to drive right past the Chief on the way.

110e095ccd82207281e31243bdf098da.jpg
 
Those aren't smoke signals behind the Chief. It's steam from the cooling towers for the twin Westinghouse 1,150 MW PWR reactors about 12 miles from me, if that gives you any hint.
 
So live around/in Oregon or Rockford?
I replaced C29 & 30 also. Sorry to ask but if I pull D10 or D11 once they are out if one is the problem will the board lose the ground and test fine or is that just dreaming as the circuit will be broken?
 
He was a big deal a long time before that, too. This whole river valley belonged to him for a while.

As for the zeners, you can lift a leg of either of them and test the unit on a DBT to see if the short is gone. It's also possible that Q8/Q10 went south, but it seems like you are definitely in the problem area.
 
OK, I pulled one leg loose on D10 and 11 and pulled Q8 and 10. No change. Next stop? Just to make sure I'm doing this right, on the ohm meter I have the - lead grounded to a screw holding the transformer with the + lead probing K and N. I also pulled Q7 and 3 with no change. Did replace the heat sink compound on Q7,8 since I was going to anyway.
Thanks.
 
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What voltage DC do you have from pin 13 and pin 14 to ground on the power supply board AWR 117
So are the fuses FU2 and FU3 ok ?

So you have the wires from AWR 117 disconnected from pins 13 and 14?

Are you using a DBT (Dim Bulb Tester)?
 
The meter connection should be acceptable for testing supply voltages as long as the transformer mounting screw is solidly grounded. Obviously, for testing components both leads will need to be free.

Just for the sake of argument, when testing supply voltages per the request of @goat67 it could be helpful to test both DC and AC to be sure a rectifier is not damaged.
 
Beautiful image of Chief Blackhawk overlooking the Rock River
We bought our first house in Andalusia Illinois. A sleepy town on the Mississippi. Worked in Moline for ten years.
I love the river. So much history.
Anyway:
I like using the DBT for troubleshooting shorts. You can build one with parts (I bet) you have in the garage.
If the lamp stays bright you have a short in the receiver. Keep disconnecting circuits until it goes dim. Of course - there's a logical sequence to help narrow it down but where's the fun in that?
 
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