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SX1250 Protection delay on shutdown

Discussion in 'Pioneer Audio' started by Ultimatt, Apr 16, 2018.

  1. Ultimatt

    Ultimatt AK Subscriber Subscriber

    Have a 1250 that powers up just fine...no pop in speakers on power up. However, on shut down there is a delay in the speaker protect relay.

    From what I can gather the relay should kick out almost instantaneously upon power off. However, I can hear the relay on this unit kick out about 1 full second after power off.

    Is this most likely a relay issue or another issue perhaps with a transistor?

    As was suggested on another thread, I removed the preamp jumpers...no speaker pop on shutdown with jumpers removed.



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  2. rcs16

    rcs16 Super Member

    Baldwin, Ontario, Canada
    That is right, instant off when working properly. I doubt it is the relay.
    The circuit uses the transformer 7.5VAC, rectifies using D4, it to produce a -ve V to keep Q4 off for normal op. Fast turn-off is accomplished since 7.5VAC goes away fast with power off, making Q4 base go high to turn it on, removing drive to Q5 and discharging C4 fast.
    Look at the DCV on the the protection ass'y, check D4(1N4148),R8,R19,C3
  3. LesE

    LesE 110284 Subscriber

    Ontario, Canada
    Are you sure it's the Protection relay that you're hearing 1 second after power off? The Soft Start relay is intended to release roughly 1 second after turning off the receiver.
    mattsd likes this.
  4. mattsd

    mattsd AK Subscriber Subscriber

    Cincinnati, Ohio
    Yep. The protection relay is instant and the click it makes turning off is muffled by the power switch click, but the soft start relay has about a second or so delay before releasing as well. @Ultimatt You didn't specify, does it pop with everything connected normally?
    Last edited: Apr 17, 2018
  5. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    If you check the rest of the protection functions you would find they are inoperative.
    Q4 2sc945a of the AWM-091 protection board has most likely failed. I have seen this before.
    Q4 is marginal over time from the heat shock of discharging C4. Called safe operating area.
    Replace with ksc2383.

    Yes, you will see correct time on delay, that's solely Q5's work. Discharging q4 turns OFF the relay current, and that discharge happens by losing the -5.1v from the power off detect d4 through c3. It also happens when Q3 says so: when there is DC offset or over current happening.

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