SX-1280 Tuner issues

Discussion in 'Pioneer Audio' started by xratedpez, Mar 27, 2013.

  1. bktheking

    bktheking Gitter Done!

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    Thanks Mark, I read your other posts on this exact chip and it's replacement issues. Fmtunerinfo has some info on other tuners that use the 4437, I believe the mitsubishi receiver had a derivative circuit to the 4438, I don't have the pdf to look at.
     
  2. rcs16

    rcs16 Super Member

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    I agree with Mark's advise. If you can not find a replacement IC.
    The SX-1250 used a reed relay for muting, so there are a few options to re-design the mute ckt as has been done with other similar ckts in other FM sections. It is basically a comparator driven from the IF signal level, having some hysteresis, a DC switch control level set by a reference voltage (switch point). Plus a element to either short the L/R to gnd or open ckt the signal s path to the o/p.
    It should not be too difficult to design your own version.
    Rick
     
  3. bktheking

    bktheking Gitter Done!

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    You sound like you know how, ill build it if you can provide a design. :)
     
  4. rcs16

    rcs16 Super Member

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    Take a look at the SX-880 tuner mute ckt! It derives the mute control from the PA-3001 detector, passes to the transistor switch, Q23 which switches the two jfets Q21,22.
    Yes it is a bit of work to do, if you can not get the original part. But the easy part for you, is that the design is done in the SX-880, so all you have to do is copy it.
    Suggest to buy a component header to replace the PA-1002-A and put the components on a prototype board.
    You will have to add the buffer as was done in the SX-880 Q6,7 and wire up the the de-emphasis filter at the o/p of the PA-1001-A. You do not need the de-emphasis selector and just hard wire to the de-emph that you need for the US, 75us, C55,56 (11nF)
    Actually, any n channel jfet should work since all that it is do is switching between pinch-off and IDSS(0V Gate-Source)
     
    Last edited: May 5, 2013
  5. xratedpez

    xratedpez Super Member

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    Still trying to get the PA1002 chip. If anyone has a lead, let me know! :)

    Keeping a watchful eye on eBay and have an ad on BarterTown.
     
  6. Dr Moriarity

    Dr Moriarity Member

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  7. markthefixer

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

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    They collect money and try to get it, then eventually refund it. Has to do with an automatic read of the Pioneer parts site and their interpretation of the response they get, which should be - fuhgedaboudit...
     
  8. xratedpez

    xratedpez Super Member

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    Update: Trying to order KB4438, possibly found a supplier thanks to BK. Will report back.
     
  9. xratedpez

    xratedpez Super Member

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    Update:

    Ordered KB4438 from Japan. Replaced PA1002A.
    FM now has output.

    Working through some alignment issues towards the high end of the FM spectrum, but we're "back online". Great news!
     
  10. markthefixer

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

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    Great!! Please PM me details about the chip / supplier / cost... Thanks mtf
     
  11. bktheking

    bktheking Gitter Done!

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    Info sent.

    Thanks
     
  12. bktheking

    bktheking Gitter Done!

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    Just to update this post- the chip came in, was installed and is working now- xrated didn't update this thread I guess.
     
  13. xratedpez

    xratedpez Super Member

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    Thought I did, guess not. Sent the chip info to many folks, including MTF. Project was a success, unit working very well.

    Thanks-=
     
  14. bktheking

    bktheking Gitter Done!

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    I want to develop a replacement, that's why I was looking at the thread :D
     
  15. markthefixer

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

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    Ok, I can confirm that the Pioneer factory shipped tuners with chips marked KB4438 in what we call the pa1002 position - I have now seen several personally..
     
  16. cbusuttil

    cbusuttil Member

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    Seems I'm reviving a thread here. have an SX-1280 with some tuner issues. when I press the FM button and turn the tuning knob, the meters seem to work and no sound. However i noticed that if i turn the volume to full on, I can hear the stations (not in stereo mode - presumably PA1001 shot?) very faith.... PA1002A? rest of the receiver works so it must be coming from the tuner section. also, when I put it on AM, the signal strength meter needle jumps full blast to the right... replaced HA1197 but with no luck -signal strength meter needle still jumps overloaded on to the right. I am not that interested to fix the AM section as i do not use it, but i wish to fix the FM section... any ideas? anyone has got a PA1002A chip for sale? thanks in advance!
     
  17. rcs16

    rcs16 Super Member

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    You need to troubleshoot the ckt a bit more, to determine where the failure is, instead of guessing where the problem is. Assumption is the the quad detector,PA3001-A is working properly, by monitoring the composite audio at Q5-6 that goes through C35 to Q6-2. Then look at the PA1001-A to determine if it locks to the 19KHz pilot and can o/p L/R or mono if no pilot is present. L/R/mono goes through the LPF(F5) into PA1002-A the de-emphasis and mute gate ckt.
     
  18. cbusuttil

    cbusuttil Member

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    Hello rcs16! thanks for your insight.... I can confirm that there is audio coming out from Q5 pin 6 ... and up to Q6, pin 2. however there is no sound at all going out from the PA1001A to the LPF. nothing. I have one PA1001A coming in a couple of weeks...
     
  19. cbusuttil

    cbusuttil Member

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    So, PA1001A arrived and i put it in the tuner. still had no output HOWEVER... the stereo indicator is working....this would mean that PA1002A is also blown. what I did in order to make the tuner sing is to short pin 3 with pin 5 (left channel) and pin 12 with pin 14 ( right channel) - you literally bypass the input with the output directly. this way you can still operate the tuner (without de emphasis, and muting and additional AF gain amplification)... tuner sounds less "gainy" and bass is a bit more flat, but still very good sound quality (crystal clear) .... I know how hard it is to find the PA1002A ... so until i find one, i still can enjoy the FM radio! I would recommend this temporary modification to anyone desperately searching for a PA1002 / PA1002A .... all in all, better than having a silent FM tuner!
     
  20. rcs16

    rcs16 Super Member

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    More troubleshooting? It could be something else other than the PA1002A.
    You need to add the deemphasis filter in order to get a flat freq response. It can be as simple as a bjt buffer or a passive ckt to get the 75us filter roll off curve.
    If you look at other designs that use a PA1001A and no PA1002A, you will see how it can be done. Not sure what they are at the top of my head, I'd have to look, but i'd start with lower end SX-x80 series receivers. like the sx-780 for example.
    I recall on post a few years back in which someone made a clone of the PA1002A . There are other methods to make a mute gate. I usually run FM with muting off as it is.
     

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