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Pioneer sx1250 D.O.A. troubleshooting

Chammycaps28

Chammycaps28

New Member
Hi everyone! This is my first repair post so please be gentle with me haha.

So a few months back I picked up a pioneer sx-1250 reciever and a sg-9500 equalizer from a rather sketchy man. I was told I could test them and that they worked great.......we've all heard that story before haha. so I show up and the house is a shack that is half torn down, with no water or power. And the gear is piled up on a cardboard box. The faceplate on the 1250 was gouged because the previous owner used a steak knife or a coat hanger to push the buttons in, and all the buttons were jammed in. And the eq had a cut off power cord. Needless to say I didn't test them. The price was cheap enough at $475 for both and the 1950s mid century kitchen from the house he was tearing down. SCORE!

So I restored the faceplate and the buttons, luckily none wore broken. And the faceplate came out scratch free.

Opened it up to check the 4 big caps, and they puked all over the bottom plate. So it was time for a rebuild. I did the following.

I replaced all electrolytic caps, tantalum caps and Transistors that were on the shoot on sight list.
The big caps came from China, and were restuffed into the original cans.
3 watt resistors on aw-106 board, protection board and power supply board upgraded from 3 watt to 5 watt.

Damage it exhibited when I got it
Awr-106 board
One transistor, 2sd325r was fried. Replaced with b31c2073.
2 resistors fried. Hot spot on half the board. Components tested fine and within spec. Except for the two resistors

Tested all tantalum caps, diodes and transistors including those that were removed, all tested fine, as per the diode test function on my multimeter.
Deoxited all pots, and switches.
Touched up all suspicious solder joints.
Tested all 8 output transistors. 7 read strong, one read on the weak side but still within spec. New mica sheets and thermal grease.

So I went to power it on, on a dim bulb tester with a 100 watt bulb.aw-048 boards disconnected top and bottom, jumpers disconnected in back. Bright bulb and no lights. No engagement from soft start relay, or protection relay

Fuses tested fine, with continuity
Thermosistor testeded fine with continuity
Soft start resistor tested fine at 3.5 ohms

Voltage readings were as follows:
At power cord coming in: 3.1vac on hot side and 1.9 on nutral.
Power supply: awr-107
Pin 1: .86vac
Pin 2: 2.22 vac
Pin 8: .51vdc
Pin 9: 2.26vdc
Pin 10: -2.06vdc
PIN 13: 1.20vdc

Stabilizer board:
Pin 1: -4.7 vdc
Pin 2: .9 vdc
Pin 3: 0 vdc
Pin 4: 1.6 vac
pin 5: 1.6 vac
Pin 6: 0 vdc
Pin 7: 0 vdc
Pin 8:0 vdc
Pin 9: 0 vdc
pin 10:0 vdc
Pin 11:0vdc
Pin 12: 0vdc
Pin 13: 0vdc
Pin 14: 0vdc
Pin 15: 0 vdc
Pin 16: 0vdc
Pin 17: 0vdc

Disconnected red plug to transformer on stabilizer board, still bright.

Disconnected plug underneath with white and brown wires going to the filter
caps and output transistors, still bright.

Disconnected red and orange plug on the protection board going to filter caps and output transistors, still bright.

Disconnected purple plug from transformer, to protection board. Went dim lights on left side came on. Powered up. Both relays clicked.

It will stay on and the light will remain dim aslong as the purple plug on the protection board and the brown and white plug on the stabilizer board are removed. Also Removed filter caps from circuit, no change.
voltage readings with purple plug and white/brown plug removed are as follows:
Power cord hot: 62.6 vac
Power cord nutral: 20.4 vac
Power supply awr-107:
Pin 1: 20.4 vac
Pin 2: 20.4 vac
Pin 8: 15.2 vdc
Pin 9: 55.1 vdc
Pin 10: -57 vdc
Pin 13: 30.2 vdc

Stabilizer board:
Pin 1: -0.47 vdc
Pin 2: 0 vdc
Pin 3: 0 vdc
Pin 4: 38.2 vac
pin 5: 38.2 vac
Pin 6: 55.4 vdc
Pin 7: 15.3 vdc
Pin 8: 7.6 vdc
Pin 9: 13.3 vdc
pin 10: 23.5 vdc
Pin 11:54 vdc
Pin 12: 0vdc
Pin 13: 56 vdc
Pin 14:23.3 vdc
Pin 15: -57.3 vdc
Pin 16: -59.8 vdc
Pin 17: 54 vdc.

These are the voltages that I got from both boards, under both conditions. I know that this post is very long winded, and I apologize for that, but you guys are unstoppable with the correct information. So I wanted to give you the best info I could. I will gratefully appreciate any help I get on getting this fixed.
Thank you everyone, I will get the voltages on the protection board tomorrow



,
 
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I think you made a classic error.

Try reconnecting both the red and purple connectors from the transformer
and DISCONNECT the brown/white (stabilizer) and red/orange (protect) connectors, see if bulb dims.

One at a time try connecting the brown/white and then the red/orange connectors and see if the bulb stays bright.

Whichever of these two causes the DBT to stay bright means that pair of big caps it's connected to weren't installed correctly.

two of the big capacitors have their NEGATIVE terminals grounded
brown wire to PLUS on a cap, it's NEGATIVE terminal grounded
red wire to PLUS on a cap, it's NEGATIVE terminal grounded

BUT THE OTHER TWO BIG CAPACITORS HAVE THEIR POSITIVE terminals grounded!!!
white wire to MINUS on a cap, it's POSITIVE terminal grounded
orange wire to MINUS on a cap, it's POSITIVE terminal grounded

A reverse connected big electrolytic capacitor looks like a short circuit.
Which is why that DBT stays bright.

for reference:
The red transformer wires (right channel) go to the (awr-106) stabilizer board and the high current diodes,
THEN the brown/white cable goes to the big capacitors
brown is +70v and this goes to a capacitor's PLUS terminal and that cap has it's minus terminal grounded
white is -70v and this goes to another capacitor's MINUS terminal and that cap has it's plus terminal grounded

The purple transformer wires (left channel ) go to the awm-091 protect board and the high current diodes,
THEN the red/orange cable goes to the big capacitors
red is +70v and this goes to a capacitor's PLUS terminal and that cap has it's minus terminal grounded
orange is -70v and this goes to another capacitor's MINUS terminal and that cap has it's plus terminal grounded

awm-091_picture_with_labels.JPG

awr-106_picture_with_labels.JPG
 
Last edited:
Chammycaps28 said:
Hi everyone! This is my first repair post so please be gentle with me haha.

So a few months back I picked up a pioneer sx-1250 reciever and a sg-9500 equalizer from a rather sketchy man. I was told I could test them and that they worked great.......we've all heard that story before haha. so I show up and the house is a shack that is half torn down, with no water or power. And the gear is piled up on a cardboard box. The faceplate on the 1250 was gouged because the previous owner used a steak knife or a coat hanger to push the buttons in, and all the buttons were jammed in. And the eq had a cut off power cord. Needless to say I didn't test them. The price was cheap enough at $475 for both and the 1950s mid century kitchen from the house he was tearing down. SCORE!

So I restored the faceplate and the buttons, luckily none wore broken. And the faceplate came out scratch free.

Opened it up to check the 4 big caps, and they puked all over the bottom plate. So it was time for a rebuild. I did the following.

I replaced all electrolytic caps, tantalum caps and Transistors that were on the shoot on sight list.
The big caps came from China, and were restuffed into the original cans.
3 watt resistors on aw-106 board, protection board and power supply board upgraded from 3 watt to 5 watt.

Damage it exhibited when I got it
Awr-106 board
One transistor, 2sd325r was fried. Replaced with b31c2073.
2 resistors fried. Hot spot on half the board. Components tested fine and within spec. Except for the two resistors

Tested all tantalum caps, diodes and transistors including those that were removed, all tested fine, as per the diode test function on my multimeter.
Deoxited all pots, and switches.
Touched up all suspicious solder joints.
Tested all 8 output transistors. 7 read strong, one read on the weak side but still within spec. New mica sheets and thermal grease.

So I went to power it on, on a dim bulb tester with a 100 watt bulb.aw-048 boards disconnected top and bottom, jumpers disconnected in back. Bright bulb and no lights. No engagement from soft start relay, or protection relay

Fuses tested fine, with continuity
Thermosistor testeded fine with continuity
Soft start resistor tested fine at 3.5 ohms

Voltage readings were as follows:
At power cord coming in: 3.1vac on hot side and 1.9 on nutral.
Power supply: awr-107
Pin 1: .86vac
Pin 2: 2.22 vac
Pin 8: .51vdc
Pin 9: 2.26vdc
Pin 10: -2.06vdc
PIN 13: 1.20vdc

Stabilizer board:
Pin 1: -4.7 vdc
Pin 2: .9 vdc
Pin 3: 0 vdc
Pin 4: 1.6 vac
pin 5: 1.6 vac
Pin 6: 0 vdc
Pin 7: 0 vdc
Pin 8:0 vdc
Pin 9: 0 vdc
pin 10:0 vdc
Pin 11:0vdc
Pin 12: 0vdc
Pin 13: 0vdc
Pin 14: 0vdc
Pin 15: 0 vdc
Pin 16: 0vdc
Pin 17: 0vdc

Disconnected red plug to transformer on stabilizer board, still bright.

Disconnected plug underneath with white and brown wires going to the filter
caps and output transistors, still bright.

Disconnected red and orange plug on the protection board going to filter caps and output transistors, still bright.

Disconnected purple plug from transformer, to protection board. Went dim lights on left side came on. Powered up. Both relays clicked.

It will stay on and the light will remain dim aslong as the purple plug on the protection board and the brown and white plug on the stabilizer board are removed. Also Removed filter caps from circuit, no change.
voltage readings with purple plug and white/brown plug removed are as follows:
Power cord hot: 62.6 vac
Power cord nutral: 20.4 vac
Power supply awr-107:
Pin 1: 20.4 vac
Pin 2: 20.4 vac
Pin 8: 15.2 vdc
Pin 9: 55.1 vdc
Pin 10: -57 vdc
Pin 13: 30.2 vdc

Stabilizer board:
Pin 1: -0.47 vdc
Pin 2: 0 vdc
Pin 3: 0 vdc
Pin 4: 38.2 vac
pin 5: 38.2 vac
Pin 6: 55.4 vdc
Pin 7: 15.3 vdc
Pin 8: 7.6 vdc
Pin 9: 13.3 vdc
pin 10: 23.5 vdc
Pin 11:54 vdc
Pin 12: 0vdc
Pin 13: 56 vdc
Pin 14:23.3 vdc
Pin 15: -57.3 vdc
Pin 16: -59.8 vdc
Pin 17: 54 vdc.

These are the voltages that I got from both boards, under both conditions. I know that this post is very long winded, and I apologize for that, but you guys are unstoppable with the correct information. So I wanted to give you the best info I could. I will gratefully appreciate any help I get on getting this fixed.
Thank you everyone, I will get the voltages on the protection board tomorrow



,
Click to expand...
We want pictures! Before during and after!
 
In the long run it’s cheaper to just buy a working receiver. I never buy something used without testing it. I’ve learned that you have to put a price on your time.
 
Mark thank you for your detailed response, I will check the caps immediately. After I reread your post several times to make sure I fully understand it.

As per the plugs, the bulb will stay bright with with both the red/orange and brown/white plugs disconnected, and the red and purple plugs inserted.

It only goes dim when the purple plug is removed, I can then reinsert the red/orange plug, and the light will remain dim. But when I insert the brown/white plug it immediately gets bright and goes into protection mode.
 
Well, I would have loved to bought a fully working one, but I don't have the funds for what they go for on ebay in the 3-4k dollar range haha. I always try to test before I buy, but sometimes you have to take a chance. Occasionally the best things in life happen by taking a chance. I try to never look at it as waiting my time, I consider it a learning experience and enjoy gaining knowledge from it. I will get this working by the end of this and I will only be into it and have a great reciver that I know was recapped correctly.
 
I'm sorry I don't have any before pictures and my ones from while I was working on it were lost on my old phone. I can take some now. Just let me know what you would li,e pictures of.
164111210759630171776197170868

164111210759630171776197170868

This the faceplate after I re machined the damaged parts.
 
Last edited:
AudioGMan said:
In the long run it’s cheaper to just buy a working receiver. I never buy something used without testing it. I’ve learned that you have to put a price on your time.
Click to expand...
I agree. But my only real option was to learn how to fix my own SX1250 if I was going to have one. There are no repair shops near me that knows what an SX1250 is. The only electronics repair shops left around here just do warranty circuit board replacements on flat screen TVs and other assorted electronic junk. I thought about sending my first one off to a still reputable tech but after speaking with him on the phone he honestly told me that a full resto would be in the $1000 range. Plus shipping two ways. That was in 2015.
 
OK, I got what you were saying about the caps, they are wired in correctly, I actually followed your instructions on another thread that you had helped on.
But there is the chance that when I restuffed the cans I could have installed a capacitor inside backwards. So I will open up the cans that are tied to the plug that is shorting out. And verify polarity
 
OK just opened up the capacitors on the right bank, verified that they were the correct polarity. Re installed, same effect.

Capacitors are installed on the right side with white to minus, plus to ground. and minus to ground, plus to brown.

Left side orange to minus, plus to ground, and minus to ground, plus to red.
 

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Brown and white:
1. Could be the outputs are installed incorrectly.
2. A pinched brown or white wire between the heatsink and chassis.

Plug the violets back in to the protection and remove the red and orange. Does the DBT remain dim?
If it does. follow steps 1 and 2 above for red and orange.

From the image: Filter caps are wired correctly.
 
I belive I found the problem, 8 bad diodes that tested 500mv both directions. I don't know how I missed these. On my initial passover, but I did. I am stupid sometimes haha. My multi meter had died, so I was using an old di-log one I had floating around until old faithful charged up. Never trust your gear haha...unless you named it old trusty, then it can never be wrong haha

This is the list of following bad components.

Awh-048
D5: 1s2473

Awh-048
D5:1s2473

Awm-091
D4: 1s2473
D6: s5151r
D7: s5151

Awr-106
D1: wz-240
D2: 1s2473
D3: 1s2473
D4: wz-240
D5: wz061
D6: 1s2473 ( good, but was clumped with the other bad ones on board)

Does anybody have a list of replacement diodes? I might have the smaller ones. But the large s5151r and s5151, got me stumped where I could find a pair except from a parts unit.
 
Chammycaps28 said:
I belive I found the problem, 8 bad diodes that tested 500mv both directions. I don't know how I missed these. On my initial passover, but I did. I am stupid sometimes haha. My multi meter had died, so I was using an old di-log one I had floating around until old faithful charged up. Never trust your gear haha...unless you named it old trusty, then it can never be wrong haha

This is the list of following bad components.

Awh-048
D5: 1s2473

Awh-048
D5:1s2473

Awm-091
D4: 1s2473
D6: s5151r
D7: s5151

Awr-106
D1: wz-240
D2: 1s2473
D3: 1s2473
D4: wz-240
D5: wz061
D6: 1s2473 ( good, but was clumped with the other bad ones on board)

Does anybody have a list of replacement diodes? I might have the smaller ones. But the large s5151r and s5151, got me stumped where I could find a pair except from a parts unit.
Click to expand...
Were these all tested out of circuit ?
 
1S2473 --- 1N4148

WZ-240 --- 24v / 500mw zener
WZ-061 --- 6.1v / 500mw zener
 
I did not test any out of circuit, I tested them with a multi meter in circuit to see if voltage passed through them in one direction, and read open load in the other direction. These are the ones that failed that test and passed voltage botavionics!

Thank you avionic! I will get those diodes ordered tomorrow.

It may have been struck, with everything else it went through it wouldn't surprise me ! Haha. Definitely wasn't expecting that, usually the diodes are still good.
 
For those who are interested these are the mouser part numbers for the current in stock substitutes for the following parts

WZ-240
Mouser pn: 78-TZX24A-TAP

WZ-061
Mouser pn: 78-1N4735A-TAP
6.2 v instead of 6.1v but should be close enough
 
reading diodes in-situ is horribly inaccurate

it's worse when there is a transformer secondary connected. You can't tell if the diode or transformer secondary is passing the meter's test current. PERIOD.
 
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