Pioneer SX 828 recapped - Relay click on and off

Discussion in 'Pioneer Audio' started by havols, Apr 23, 2017.

  1. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Well Larry
    Do not be in any hurry to respond. My condolences.
    I will post the results here, otherwise I will forget it.
    I removed the relay, and cleaned
    Then, with the voltage of the receiver set to 130V, I connected on the wall, to 133VAC.
    It works fine, for 10 minutes, using a headphone. Volume around 20%. tuner, aux and phono.
    So I power it off, and install one speaker (Marantz 87 dB sensitivity)
    After, I power on in wall (now with 135 ... 136VAC). It runs OK for 3 mnutes, and when i turn up the volume (around 50%), the relay click on, and no soung again.
    After that, I had no sound. The relay is not activating again. No more sound... MUTE.
    All capacitors have been replaced, except C6, C7 (main filter)

    The offset on power amp is 0V
    The bias voltage
    L: 28mV
    R: 15mV
    Both Bias Adjust VRs are in the minimum position.

    I found high voltages on PINs 20 and 9 of power amp board. The same voltage that PIN 23
    PIN 20: -45VDC
    PIN: 9:45 VDC
    PIN 23: -45VDC

    In the service manual, voltages of PINs 20 and 9 is (-39VDC and 39VDC). And voltage on PIN 23 is -45VDC.
    Maybe there`s a poblem here.
    I really tired with this receiver. I have worked a lot on it, for a looong time, more than year...... arrrrhh. but i like it, and I will not give up

    Regards to you.
    Sincere condolences.
     
  2. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Hang in there you will get it going. Any reason you didn't just go ahead and replace all the transistors? Usually, I will replace all ecaps, transistors and diodes on the power supply. I figure while I am in there I will just get fresh parts in. Usually I do the same with the protect board, amps and control boards too. I know its a shot gun method, but it seems to work for me. I do one board at a time, take voltages and verify that board is working properly before moving to the next.
     
  3. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Thanks for reply loweran
    Here, some transistors are hard to find.
    But can i follow your suggestion, except the output transistors. (i think they are fine)
    Maybe i have to buy some transistors in other state.
    Then, the voltages on power supply are fine, like schematic. I replaced all caps, and Q1 and Q3 transistors.
    In protection board, all voltages are OK, except pin 9, that i measure 34V.
    In power amp board, voltages are fine too, except pins 9 and 20 (measured 45VDC; -45VDC - schematic 39VDC; -39VDC)
    In your opinion, where wish have i work now?
    best regard
     
  4. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Well, I am no expert like some of the others including Larry. But, it seems your issue is intermittent, meaning sometimes it works, sometimes it does not. That may mean that a transistor is working sometimes and not at other times. I have used compressed air to track one of those down before. I just gave a little squirt of are with the can inverted. Does not take much. I found a bad transistor as soon at the air hit it.
    I am also curious if you have access to different speakers and have tried that. I had a set of speakers and one of the tensile leads from the coil was frayed. Occasionally, it would short and cause the protection to trip. Also, I had a receiver that I had installed a transistor incorrectly. It worked, but when I turned it up, it went into protection. You may double check all your work just to be sure. You can look at the data sheet on the transistor to ensure you know the order of the leads. You may know all this, but I am not sure how much experience you have with these things. I have only been at it for a couple of years.

    For clarification, when you say power amp board, I assume you mean the main amp board and not the power supply board. correct?

    Also, did it work before you re-capped it?
     
    Last edited: Oct 23, 2017
  5. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    I don't have the schematic infront of me, but is +-45 your rail voltage? Are you shorted? Do you have this on a DBT?
     
  6. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Right loweran
    I have experience a bit. Not much. But seems a good idea to do a re-check on my service.
    I tested with different speakers. Marantz 87db, pioneer cs 66G, headphones without speakers plugged .. The problem in on receiver.
    The voltages that i measure, was done with receiver with relay act on (mute). So, if have a bad transistor, the voltages wish be altered?

    Yep, main amp board. Sorry

    No. so I started the full recap, and I want to leave it 100%.

    What occurs... cools bad transistor?

    Regards
     
  7. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    DBT is a buck transformer? Yep, 133VAC on the wall, and 116VAC after buck transformer, to receiver..
    I annexed the main amp scheme
    Regards
     

    Attached Files:

  8. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Yes, I think that sometimes the change in temperature causes them to reveal that they have an issue. In my case, the cool air caused the issue to reveal itself. Sounds like you have an issue with a transistor somewhere. It may not even be one of the ones you changed. Someone with more background can probably help you pin point that by tracing the voltages. Sounds like you are close though.
     
  9. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    DBT is a homemade device that puts an incandescent light bulb before the power to the receiver. If you have a short, the light bulb takes the power so your components do not. This will save your outputs and other when doing work on the unit and you create a short. You can google it to see how to build it.
     
  10. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Ohh. I have a DBT... Dim Bulb Test
    I always use it after some service
    I will test with it tomorrow again. Before the last relay clic-on, when it function OK, there's no short. I have tested.... but after, i did not tested it.
    Thank lower. I will recheck some points tomorrow, and post results here.
    I appreciate your help
    Best regards from Brazil.
     
  11. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Good luck!
     
  12. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Loweran
    No short.
    I checked transistors that i replaced. All OK.

    So, the situation stills the same. Relay click active. I measured all voltages on Power Supply, Protection Board and Main Amp Board.
    All voltages is OK, except the above listed:
    PIN 9 Protection Board: Measured 34 VDC (8VDC on scheme)
    PIN 20 and PIN 9 of Main Amp: Measured -44VDC ; 44VDC (-39VDC ; 39VDC on scheme). Offset and Bias is OK.
    All Voltages on Power supply is OK with scheme.

    I measure this VDC voltages on q5, q6, q7 transistors on protection board (AWM025)
    Q5:
    B: 10.8V
    C: 0.69V
    E: 11.6V

    Q6:
    B: 0.68V
    C: 8mV
    E: 0V

    Q7:
    B: 8mV
    C: 34.2 V
    E: 0V
    So, if someone can help me to find what the cause of relay click on. I would be grateful
    Best regards
     
  13. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    You are going to need someone with more experience than me on this one then. Maybe it's as simple as the relay itself, but the voltages look off for some reason. I redid an sx-1010 and only replace some of the transistors, and it had issues. Replaced the rest of them and it worked perfectly. That is why I asked you about replacing all the transistors. Now, since you don't have easy access, you may want to get someone who can help you pinpoint the issue and fix the root cause only.
     
  14. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

    Messages:
    4,093
    Location:
    Las Vegas Nevada
    Monitor the base voltage on Q7 of the protection board and see if it's changing when in and out of protection.
    Reflow the connections at the emitters (R15 and R16) and henry coils located on the power supply board.
     
  15. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Thanks loweran and zebulon
    Right Zebulon.
    I reflow the connections on resistors and coils.
    Clipped multimeter on ground and Base Q7
    In protection mode: 8mV, and after a time this voltage are increasing and decreasing (40mV...50 mV.. 150mV... 8V!!). And go out protection mode.
    When voltage on Base of Q7 is 8V, i listen relay click, and go out of protection mode. I heard music on outputs.
    But, a 30 seconds later, relay click again, voltage on Base Q7 return to 8mV, and go to protection mode.
    This is the situation.
    The problem can be o protection board?
    On protection board, i just have replaced the Q6 and Q7 transistors. The Q1, Q2, Q3, Q4 and Q 5 stills original

    Maybe wish i have to replace all transistors of this board?
    Thanks for your help
     
  16. LesE

    LesE 110284 Subscriber

    Messages:
    634
    Location:
    Ontario, Canada
    It seems to me that the AWM-025 Q5 base voltage is too low which is causing it to be in the "on" state preventing the relay from energizing. In one of your previous posts, you indicated that the cathode of D5 is low which may point to the overload dectection circuit. If the cathode of D5 is still measuring low, you could try removing Q1 and Q2 to see if it results in a solid activation of the relay.

    Les
     
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  17. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Yes Les
    I checked again and Cathode of D5 had 10V.
    D7 and D6 cathode's had 20V

    Do I want to remove Q1 and Q2 completely (3 legs) from the board?
    Then turn on and check the voltage at the base of Q7, and if the relay active correctly?
    No risk to the main amplifier, right?

    Thank you very much
     
  18. LesE

    LesE 110284 Subscriber

    Messages:
    634
    Location:
    Ontario, Canada
    I don't believe there is any risk of operating with Q1 and Q2 removed except that overload protection will be disabled.

    Les
     
  19. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Thanks Else.
    I am afraid because here is hard to find some components... and i want to preserve output transistors.
    This procedure will show if Q1 and Q2 are fail? D1, D2, D3 & D4 too?
    Havols
     
  20. LesE

    LesE 110284 Subscriber

    Messages:
    634
    Location:
    Ontario, Canada
    I understand your concern. You could just go ahead and replace Q1 and Q2 in speculation to preserve the overload protection circuit. Either way, it would be advisable to monitor the circuit inputs by measuring across pins 5 & 6 and 7 & 8 to ensure that there isn't a legitimate overload condition that is triggering protection which could damage your outputs or speakers.
     

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