SX-727 Aux only, no phono or tuner working

Discussion in 'Pioneer Audio' started by Greg111111, Feb 11, 2018.

  1. Greg111111

    Greg111111 New Member

    Messages:
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    Hi All,

    I have a problem with my SX-727. Currently, no sound from the phono or am/fm tuner. Aux works fine, as well as the tape monitor.

    For a little backstory, I've been hacking away at this thing for a few years now. (thanks to the helpful info in this forum). I've replaced the majority of the Caps, as well as replaced bulbs, cleaned with De-Oxit and replaced some transistors. Everything has always worked, somewhere along the way, however, I lost my Phono and Tuner output. (I primarily listen to the Aux). The tuning and signal meters seem to be working, just no sound.

    The last change I made was replacing the whole head amp board. (long story short, I fried some of the tracings trying to get at the transistors.). I attached my new board via wire splicing the 10 connectors (probably not the most professional method), but I did check for continuity and all seemed good.

    Any ideas for some simple things I can check to help get the phono back?
     

     

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  2. audiomaniac2

    audiomaniac2 Member

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    Location:
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    check for correct voltages on phono and am/fm boards.
     
  3. markthefixer

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

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    The aux goes in AFTER the head amp W21-002 board. Loss of that board will kill AM, FM, FM AUTO, PHONO1, PHONO 2 and MIC. It switches equalization for the various sources - that is as important as the power for correct operation.

    Quick and dirty tests: wet the tip of your finger, and touch it first to the out1 and then out2 connections - in any position but aux - should hear a buzz in that channel and then the other channel.
    Then touch the in1 and in2, should get louder buzzes, depending upon if it's set for AM, FM, louder: mic, really loud Phono1 or 2.
    Check for +25 or 30v at the +B connection.
    Post a picture of the board so we can check transistor installation orientation.
     
  4. Greg111111

    Greg111111 New Member

    Messages:
    10
    Thank you both for responding.

    Mark, I'm getting 30v at B+. in1 and in2.. i can a hear a little popping, out2 good buzz, out1 nothing.

    IMG_1542.JPG
     
  5. Greg111111

    Greg111111 New Member

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    Ok, a little victory. Phono and FM/AM are now working! Q1 (i think it was Q1) was not orientated properly. Thank you Mark for steering me towards this board, the side to focus on and the transistor orientation.

    Bad news, they only work in Mono. No sound from the right channel, unless mono button is pressed. Would that possibly be related to this same board? (Stereo used to work at some point in my tinkering, and I have de-oxited all of the buttons.)
     
  6. markthefixer

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

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    Well I had a post, but forgot to hit reply!! The auto save kept it overnight. I saw what looks like a clipped piece of wire laying on the left (right channel) side, but if you remounted a transistor it could have moved or fallen away.

    SX-727_W21-002.JPG

    When you switch to mono You are COMBINING the left and right channels and sending the combined signal to both the left and right preamp and power amp circuits.

    That means that the RIGHT channel of that board is dead. Q1 was probably destroyed when it was put in improperly.

    If that wire shorted out the power on your first tries, yet moved for "your little victory" to allow the left side to work when the power came back, it could have left behind a damaged transistor.

    Can you post another picture of the board - maybe from the opposite angle?
     

     

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  7. Greg111111

    Greg111111 New Member

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    Hi Mark,

    I found that wire last night as well, that was a recent addition from the night before. (I might not have even turned the power on with it in place.) . But regardless, just so I understand what we're talking about:

    If Q1 was destroyed when put in wrong, wouldn't I have had no sound in MONO before I began? Does it matter if it's destroyed in the wrong orientation vs destroyed but put in the right way? (of course it's very possible I destroyed it when I put it right).

    I will take some more pictures tonight. Thanks again.
     
  8. markthefixer

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

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    Nope,

    head amp precedes some switches, and then the volume control and balance amp and tone controls. So the loss of one channel isn't as noticeable in Mono.
     
  9. Greg111111

    Greg111111 New Member

    Messages:
    10
    Sorry, I mis-spoke, I meant to say:

    Transistor - wrong orientation - no mono (no sound at all)
    Dead Transistor - right orientation - we have mono

    With my question being, so a working transistor in the wrong way, produces a different output (a totally dead board?, no sound) than a dead transistor, correct orientation (1/2 dead board, sound in mono only). Probably a moot point, just wanted wrap my head around the whole thing.

    So I took some more pics of the board (don't mind my temp wire connector), apologize, my shop light is right above and tough to not get a shadow. But I also tested a few of the transistors with multimeter (included the one I just replaced), and I was able to get similar readings with the diode setting of .680ish on both legs, for what that's worth.

    Thanks again

    IMG_1545.JPG IMG_1545.JPG IMG_1546.JPG IMG_1547.JPG IMG_1548.JPG
     
  10. markthefixer

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

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    Transistor installed in the wrong way GETS dead, and in getting dead, can pull the power supply down to where the other channel cannot operate either. The power supply voltage is derived from the voltage drop of a 330 ohm and 100 ohm resistors. 6 volt drop across 430 ohms is 14mA of normal current draw.
    If the resistor's output (pin 5 or 6) is shorted, the maximum current flowing is 107mA - which will not destroy the power supply. As an added bonus, the loss of the 30v also would shut down the AF unit, and thus absolutely NO chance of sound...

    Now, that dead transistor installed the right way no longer kills the power for the other channel, so the other channel now works, while the channel that needs an operating transistor will not work. Power also flows to the AF unit (volume / tone etc) so there is a strong chance of sound.

    Now, as for installing transistors:
    These replacements are ECB layout. With the flat FACING you the leftmost lead is the emitter, the center is the collector and the rightmost is the base.

    to-92.png

    To install, draw an imaginary line in your mind between the emitter hole on the pc board and the base hole on the pc board of that transistor .
    Then take the leftmost lead and put it in the emitter hole.
    Then rotate the transistor until the rightmost lead is closest to the base, then stick it in the base hole.
    That leaves the collector hole either in front of or behind the imaginary line between the emitter and the base.
    BEND the center lead to that hole and put it in.

    Ta DAAA, the transistor is installed.

    To rehash, locate the emitter on the transistor
    put it in the emitter hole
    rotate transistor until base lead is closest to base hole.
    put base lead into base hole.
    then bend the center collector lead forward or backwards to the collector hole
    put collector lead in collector hole.

    I've been tying my optic nerve into knots trying to interpret the pictures,
    and something about the installation doesn't LOOK right - but I cannot put my finger on it.

    The darkness in the pictures is not an issue, I stuff each into a photo editor program and goof with parameters to clear things up.
     
    Last edited: Feb 17, 2018
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    I took the 727 board drawing and Printed a full page version and took a couple transistors and put them in from the opposite side after I verified the pinout from the component side with a flashlight thru the paper. Q2-4-6 looked suspect at 1st glance. Q1-3-5 are probably ok as he has one channel.

    It looks like Q2-4-6 might be in backwards. The board drawing in the manual is from the SOLDER SIDE not the component side. The way I'm looking at the thing is Q2 should be facing away from the pins IN2, B, OUT 2 and T2, with the Collector behind the transistor (under the curved side). Q4 should be facing directly toward IN2 collector behind, and Q6 should be facing toward Q4, collector behind. This is based on ECB. I'd recheck Q1-3-5 also.

    Just for Re-Enforcement
    Transistor pinout.JPG

    Mark can you verify as I'm almost 100% but there is always that doubt with me and transistors. Either that or Gibb's slap me (again)

    Larry
     

     

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  12. Greg111111

    Greg111111 New Member

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    Thank you Mark for the description dead vs. dying transistor in regards to the effect on the board. That makes sense.

    If these transistors are placed incorrect it's unfortunately ironic, the whole reason I bought this new board off ebay is because it had the transistors replaced already and I had such an awful time replacing them on my original. I kept getting confused with orientation and soldering them in and out and just got super frustrated that I gladly welcomed splicing all the wires for a new board! (which was a PITA too!)

    Here's another photo of Q2,4,6 from a better phone. (Thanks for joining the fun Larry!)

    I know we can't see all the legs, but I've been staring at all 6 of these and I THINK they're all consistent with each other in regards to the ECB graphics printed on the board.

    It probably doesn't matter, but I do see the capacitor values in regards to Volts are higher than what I replaced with on my original (63v) the uf is the same though.

    IMG_2522.JPG
     
  13. Greg111111

    Greg111111 New Member

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    FWIW, I was just poking around with my multimeter and I am getting the same measurements comparing voltages on caps and transistors from channel 1 to channel 2.
     
  14. markthefixer

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

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    Repeat the wet finger experiment on in1 and in2 with the volume turned down enough that it will not be damaging to your speakers...
    ALSO report which "IN" comes out on which speaker.

    Then touch the wet finger to out 1 and then to out 2, turning up the volume until you can hear the buzz when you touch them. Report results.
    ALSO report which "OUT" comes out on which speaker.

    You spliced in another board.... sigh, that compounds the possibilities.

    Also do the wet finger test on the AF unit, AWK-010 pin 9 and pin 11
    ALSO report which "pin x" comes out on which speaker.

    Seller replaced transistors? I couldn't find the closed auction. Who?
     
  15. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    63v caps won't hurt anything. If the values are same or slightly higher (no more than 20%) you're ok with regard to cap sizing.
     
  16. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    I did a copy and paste to Paint and determined the layout's of all 6 Transistors on 2 pages (one for Q1-3-5 and one for Q2-4-6) Then marked the Facing orientation based on a KSA992. ARROW is pointing AWAY from the FLAT FACE ON ALL TRANSISTORS. Q2-4-6 have collectors BEHIND the Rounded side of the transistor, while Q1-3-5 have the Collector in Front of the FLAT FACE of the Transistor. Comparing these drawings from the front side with the PINS on the bottom, with the pics, it definitely looks like transistors are in wrong from face orientation. UNLESS the Transistors aren't what we expect. Greg. Can you verify the numbering on all the transistors please. If the Transistors are BCE or EBC then the orientation of the transistors on the boards make perfect sense to me. But I can't see the numbers on the transistors.

    On the DRAWINGS BELOW, Orientation of the transistors will be the same front vs. back on the board. The arrows are based on a ECB pin out for the KSA992. For the 2sc458 rotate 180deg. Remember the drawing is from the solder side of the board. For ECB Face orientation will be the same basic direction as the drawings, toward the pins, away from the pins or for Q3 &Q4 toward the center of the board or toward the corner of the board at the pins. Orient yourself with the Edge pins toward you. Then compare Each drawing with your board and transistors. If the transistors are KSA992's then it looks to me that at least 1/2 of them are installed wrong if not all of them. If 2sc458's most likely correct. If another transistor (EBC or BCE) they may be correct for 1/2 of them or all of them. We need to know exactly what transistors are in it.


    Q1-3-5
    SX-727 Q-1-3-5.JPG

    Q2-4-6
    SX-727 Q2-4-6.JPG
     

     

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  17. Greg111111

    Greg111111 New Member

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    FIXED! The "In2" connection wire (my splice) was bad. While I had continuity, there was some shorting going on where the black and white wires join together. Thank you Mark, it was your prompting to repeat the wet finger test (with the transistor properly oriented), that showed that In2 was not functioning. When I first did the finger test, with the bad transistor, I got very faint popping from in1 and in2, which now i know was not the sound I was looking for. Once the board came back to life, I could clearly hear the sound for in1 and nothing for in2.

    Larry thank you for time digging into the transistor info, before I put the receiver all back together I meant to get the transistor codes just to ease our minds, and I totally forgot, sorry.

    Now that I've got my 727 back, I can start re-capping the backup (535), I see there is another thread going about that! Thank you both again!
     
  18. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Good Job. If/When you get back in the 727, do check the transistor numbers, please.
     
  19. markthefixer

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

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    Good Show!!!

    Saves me a bit of effort, I was strongly thinking about following Larry's lead and printing out a board layout, and then sticking in some transistors, caps and wire wrap pins and taking / posting pictures.
     

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