Pioneer SX-1250 will not come out of protection mode

Discussion in 'Pioneer Audio' started by corpblues, Oct 3, 2017.

  1. corpblues

    corpblues AK Member Subscriber

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    I recently bought a pioneer SX-1250 and the seller pulled a switcheroo and delivered a different non-working unit instead. Story if you are interested http://audiokarma.org/forums/index.php?threads/scammed-on-craigslist-for-a-pioneer-sx-1250.790565/

    Moving on to diagnosing the receiver. It powers up, which I think is called the soft start, but does not come out of protection mode. I don't see any obvious damage. The protection relay will sometimes engage momentarily but immediately kick back off. Most of the time it does not engage at at all.

    I would like to diagnose to know what I am dealing with. Unless the repair is easy I'll probably end up taking it to a professional tech to not risk further damaing it.

    My repair skills are cosmetic, mechanical, knobs, fuses, lights, cleaning and deoxit. I have cleaned up about 20 receivers that turned out great. I do have a multimeter and conceptual idea how it works. I am fairly intelligent or at least been told that and fairly handy. But I have zero education or knowledge of electronic repair. With your help I can hopefully diagnois this receiver.

    Let me know if you are interested in slowly stepping me through diagnosing this receiver.

    Thanks in advance,
    David
     
  2. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    3,995
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    Read THIS first and see if you have the minimal equipment and skill to tackle this 1250 check out.
    A DMM with a good set of micro clip leads will give the info we need. If you want to attempt a repair more equipment will be needed.
     
  3. corpblues

    corpblues AK Member Subscriber

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    I read that thread, makes me want to go buy all that equipment. Probalby will when I retire in a few years.

    I do have a DMM (Sears craftman 82141) and I will order a good set of micro clip leads from amazon.

    Will do my best to proide the info you need. Appreciate the opportunity to learn.
     
  4. njcanuck

    njcanuck aka: MacGyver Subscriber

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    I had a similar issue with a NOS Harman Kardon unit. It turned out to be a bad (old) capacitor in the protection circuit. Obviously, it could be something more serious but that is where I would start.
     
  5. SaturationPt

    SaturationPt AK Subscriber Subscriber

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    Location:
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    Reading this and the associated thread about your skills and a trusted tech nearby, I would take this to your tech.

    You can check the power supply voltages and make the amplifier adjustments that are in the Service Manual to see if that is all that is causing your problem, very possible that it is.

    Getting it to work is probably a simple fix, could be DC offset, could be that the protection board needs to be rebuilt, might need one or both power boards serviced, there are several possibilities. However, if the tech is good and you trust him, the easy fix will be an inexpensive fix.

    The other side of this is that the SX-1250 is a complicated beast which has several opportunities within to reverse a transistor or capacitor and cause expensive collateral damage, ... and techs always hate working on someone else's botched repairs. This will increase your costs exponentially. Also, just fixing a 1250 isn't enough, going completely through it to restore it electronically is what it deserves and what should be done to get it into the $1,000+ range (although most sellers bend the truth a bit on what "serviced", "re-capped", and "restored" mean).
     
  6. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    3,995
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    SaturationPT is handing out some good advice. The steps I outline if followed can be done safely will give an idea to whats going on. Its not too complicated and has a low probability of self induced damage.
    If you can get through this, you can re-access your idea of a repair.
    With the set on:
    Voltage readings in DCv's from the Protection board AWM-091 Pins 1, 3, 5, 9 and 6.
    ACv readings from Pin 2.
    Protection board is the second from the left looking from the front. The pins are accessed from the white Molex plugs at the bottom of the chassis.
    I rest the receiver on its right side, bringing the bottom of the board to the top where its easy to see.
    At this point the probes you have will work but may be modified with a sharp tip. The Molex wire sockets are recessed into the plastic plugs and you have to get in there to read the voltages.
    A stiff, bare 18 gage(?) wire wrapped around the red probes tip will work. Don't make to long as too short it against the chassis cutout. You could tape the bare section leaving a small portion of the tip exposed.
    Black probe gets grounded to the chassis. I'll find a hole in the chassis to rest it in.
    Some voltages should read in the tens of volts, others will be in the millivolts (0.000) range. If your DMM doesn't auto range, you might have to select a higher or lower range to see the voltages.
    It will take a little time for you to figure out the service manual image and the actual board. The SM board image is a mirror image and can cause some confusion when actually looking at the receiver.

    Checking these voltages will give us a good idea of whats going on with the set.
    The micro clips are for checking the voltages at the Power supply test points where the close components can cause unintended damage.
     
    Last edited: Oct 4, 2017
    SaturationPt likes this.
  7. corpblues

    corpblues AK Member Subscriber

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    Thank you zebulon1. I will follow your instructions this weekend and report back.

    I have been taught by a tech to not use the spray deoxit as it makes a mess and some techs will not work on a device that has been sprayed. Taught me to use deoxit liquid and use small drops.
     
  8. corpblues

    corpblues AK Member Subscriber

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    Need some direction to make sure I take the measurement correctly. I do not see the pins labeled so not certain which side is pin #1. I have the receiver up on its right side as directed.

    Which is pin #1, the first one on the left or right in this picture.

    Also, to measure can I fully disconnect the plug and stick the probe into the plug pin hole. Or does the plug still need to be connected to the pins and pulled just loose enough to alllow the probe to touch the pin?
    IMG_7150.JPG
     
  9. corpblues

    corpblues AK Member Subscriber

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    Brief update. I found some of the pins on the amp connector pins very tarnished. I cleaned them up but didn't fix it.

    I also noticed that the lights on the speaker a/b/c and function selected am/fm/phono/aux are not working. The 4 big display lights do work fine.

    It will engage the relay every once in a while for a few seconds and a few times for about a minute. I can hear the quiet white noise on headphones when it does this. Then goes quiet when the protection relay disenages. So I think there is life waiting to be restored in this unit.

    Still waiting for some advice about how I connected the dmm lead to the pin properly.

    I've told my tech I'll be bringing it to him in a few weeks. I would still would like to be able, with your help, diagnose it just a bit first.
     
  10. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    3,995
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    Switch a rue.
    We got to look at the power supply voltages.
    Same procedure to check them.
    Read from the bottom of the set.
    The stabilizer board is the second from the right.
    Pins 1, 2, 3 are the first threezy Molex plug. The service manual board illustrations are mirror images. Pins 4 and 5 are AC voltage, Pin 3 is ground.
    Leave the Molex plugs connected.
    Get familiar with the service manual.

    Maybe its time to have the tech look at it. Possible Stabilizer rebuild.
     
  11. SaturationPt

    SaturationPt AK Subscriber Subscriber

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    Location:
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    Please understand that every time you power it up, you risk causing additional / collateral damage. Where it is possible that your tech will do this also, especially if this is his first SX-1250, I would suggest that it is money well spent moving this unit to a competent tech. You will probably save money sending at least the stabilizer board and power board to one of the guys on this forum who have rebuilt many (such as zeb above if he's interested), get them back rebuilt and then do a slow power-on (dim-bulb or variac). The power supply problem might be a symptom of a larger downstream problem or it might be the whole problem. It sounds like this unit will benefit from a complete restoration.

    A cardiologist, no matter how skilled, is usually not going to do brain surgery on a friend even if walked through it by a skilled neurologist. My opinion is to stick with what you do well or learn on a less-expensive / lower risk unit.
     
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  12. corpblues

    corpblues AK Member Subscriber

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    Here are the readings I obtained.

    The readings on some of the pins went up and down like a wave, not sure if they is the expected behavior.
    Perhaps a better DMM would make obtaining the values more accurate or perhaps this these values demonstrate the need for a rebuild

    As you know this thing weights a ton. Like the idea of shipping just the power board and stabalizer board, but that seems risky as other boards might also need repaired.

    FYI - I just bought a 2nd SX-1250 in similar condition but have not picked it up yet. My rational is to build one working unit out of two My plan is to take both non-working units to my tech in a few weeks to have him diagnose and recommend the best course of action. I expect to be in pretty deep by the time I get up and running. I read one AK chain where several individuals spent about $1K for a restore. I'm hoping I can get it up and running for around $300 so I know what more I'm dealing with.

    I considered pin 1 the pin closest to the back of the receiver. Let me know if I had it backwards. I could not figure out from the diagrams which side was pin 1 and I can't see what is printed on the card without pulling them out of the receiver.

    Protection Board
    pin 1 = 0
    pin 2 = .8 to 0 (AC) seems to count down when the probe is touched to the pin.
    pin 3 = -110 to 110. counts down then up and then down, then up
    pin 5 = 0
    pin 6 = -110 to 110. counts down then up and then down, then up
    pin 9 = .3

    Stabalizer
    pin 1 = -.4 to .4
    pin 2 = -.4
    pin 3 = 0
    pin 4 = 52.0 AC
    pin 5 = 0 AC
     
    Last edited: Oct 9, 2017
  13. corpblues

    corpblues AK Member Subscriber

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    Since there are only 2 screws that hold the protection board in, I removed it and now see I had the pins numbers backwards. The board looked good but the backside had sticky substance on it.

    I definitly need a better DMM if I am going to do this again. This sears DMM seems hard to get a steady reading or maybe it is just me.

    New measurements for protection board with the proper pins locations.

    Protection Board
    pin 1 = 65.5
    pin 2 = 7.4
    pin 3 = 23.4
    pin 5 = 7.7
    pin 6 = .4
    pin 9 = .4 to zero

    I also gathered measurements on the stabalizer board. Found a picture of one removed online so I was able to figure out the correct pins

    Stabalizer
    pin 1 = 71
    pin 2 = 71
    pin 3 = 0
    pin 4 = 53.5 AC
    pin 5 = 53.5 AC

    Learned enough to not take any more risks messing with it.
     
    Last edited: Oct 9, 2017
  14. SaturationPt

    SaturationPt AK Subscriber Subscriber

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    The 1250 has a lot of parts and the restoration part count is much higher than most receivers because of it. The nice part however is that the boards are plugged in, and the boards are marked well so that following the schematic is easy.

    Look at the stabilizer board and see if it has discolored from heat. Some have, some have not. If the board is discolored and the wrap on some of the electrolytic caps has shrunk enough to expose the entire top surface, ... it's definitely going to need a complete restoration on that board.
     
  15. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    Take all the pin readings on the stabilizer board. There are several different voltages to check on that board.
    So far so good with the readings.
    Note: Place the negative sign (-) when reading negative voltage.
     
  16. corpblues

    corpblues AK Member Subscriber

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    Stabalizer AWR-106

    pin 1 = -72.1
    pin 2 = 72.2
    pin 3 = 0
    pin 4 = 53.5 AC
    pin 5 = 53.5 AC
    pin 6 = 88.9
    pin 7 = 25.7
    pin 8 = 0
    pin 9 = 0
    pin 10 = 23.9
    pin 11 = 65.7
    pin 12 = 0
    pin 13 = -65.9
    pin 14 = -23.4
    pin 15 = -89.5

    The board is dirty but I don't see an obvious discolored or burn looking marks.
    I did use an eraser to clean the pins as some of them were very dirty.
     
    Last edited: Oct 10, 2017
  17. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    The tuners 13.5v is missing as well as the 5.4v for the lamps.
    Stabilizer needs rebuild or a fuse.
    But the missing voltage on Pins 8 and 9 wouldn't affect the amps operation. All the other voltages look OK.

    Back the to protection board and read the voltages like you did on the Stabilizer.
    This voltage check will tell us if the amps are adjusted correctly.
     
    Last edited: Oct 11, 2017
  18. corpblues

    corpblues AK Member Subscriber

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    647
    Location:
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    Protection Board AWM-091

    pin 1 = 65.3
    pin 2 = 7.6 AC
    pin 3 = -23.1
    pin 4 = 0
    pin 5 = 5
    pin 6 = 0
    pin 7 = 0
    pin 8 = 0
    pin 9 = 0
    pin 10 = .10
    pin 11 = 0
    pin 12 = 73.5
    pin 13 = -73.2
    pin 14 = 0
     
  19. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    3,995
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    Expected readings for the protect board AWM-091 (Regarding the amplifier inputs):
    pin 1 +65v DC,
    pin 2 7.5v AC
    pin 3 -24v DC
    pin 5 closer to +20v DC or +3v DC if overcurrent triggering
    pin 6 0.000v DC
    pin 9 0.000v DC

    One of the Amplifier boards and or outputs is needs attention.

    It looks like a complete rebuild of the Power supply (or a fuse) and one or both amplifiers.
    Once the missing voltages are restored you may find more issues.
    It's a little bit of a wreck but it will sing better than new again. You might have to spring for a set of outputs but the costs to get it running shouldn't be to bad.
     
    Last edited: Oct 11, 2017
  20. corpblues

    corpblues AK Member Subscriber

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    Location:
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    zebulon1,

    Thank you for the diagnostic assistance and your patience. I learned a lot throught this diagnostic process.

    Perhaps I'll replace all the fuses and clean the rest up the pins on the other boards as a last ditch mircle long shot.

    It will be going to my tech as soon as I save up the repair money. I've already way got too much in this unit as-is but bothers me selling a non-working receiver. If I end up coming out even and someone getting a quality working receiver it will be worth it.

    I noticed the two high volt readings on the stabalizer board and was hoping adjusting them would be the recommendation. (I have not adjusted anything). But seems it needs the care of a professional experienced skilled hands to rebuild the failed components and bring it back to life.
     
    Last edited: Oct 12, 2017
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