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  1. merlynski

    Pioneer sx1080 "smoker project"

    D5 backwards make the bias spreader go full open, turns on the driver transistors (Q6, Q7) into saturation and puts the full +/-62v supplies voltage across R14 and R15. If the outputs are connected they go into saturation also, taking out the output transistors and often their 0.5Ω emitter...
  2. merlynski

    Pioneer SX780 Restoration

    Well, there are other Vintage Pioneers that look just as good that pump out more power. You may have to refurbish one to get it reliable, but that can be done.
  3. merlynski

    Pioneer SX780 Restoration

    Spot on question! The 150mV spec means that a 150mVRMS signal will drive the output power to (at least) its rated maximum with the volume control maximized (into 8Ω). If you are driving it with a larger signal then the maximum output will be reached before the volume control is rotated fully...
  4. merlynski

    Pioneer sx1080 "smoker project"

    If the output transistors are unplugged the most likely candidates for smoke are R15 and R14 (maybe R11). Check that VR1 (bias adjust is set to 0Ω and D5 (STV-4) is not backwards or open. Look also at orientation of Q3, Q4, Q5.
  5. merlynski

    Pioneer sx1080 "smoker project"

    You are not the first to install parts incorrectly, and will not be the last, we have all done it. Not a waste of time, I am here to help. Part of the process I did not recognize at the start of my time on AK, was learning the skill level and communication abilities of the person I am helping...
  6. merlynski

    Pioneer SX780 Restoration

    Welcome to Audiokarma, sebas1983! The voltage to the STKs is an unregulated voltage and normally drops under load, If you look on the schematic, near pin 11, there is a voltage listed: 40v is the no load voltage, the number in (34) is the 'nominal' full rated load voltage. Yours do not seem to...
  7. merlynski

    Pioneer SX-750 Goodwill Special

    What point do you mean by: "touched the power supply" From the electronics perspective you have to look at the voltage difference and the current available. Distance does not matter, only impedance. The rising voltage present will push current through the lowest impedance first, then as that...
  8. merlynski

    SX-880 with protection issues

    The Original Poster that created this thread also created the title, which indicates this thread is about his SX-880 and its problem with Protection issues. The normal protocol is that the focus of the thread is on the subject that it was originally created for, rather than a general 'Protection...
  9. merlynski

    Pioneer sx1080 "smoker project"

    Asking for verification: Output transistors are unplugged? It smoked after the Protection relay pulled in? Can you tell which component smoked?
  10. merlynski

    SX-880 with protection issues

    @mgl99 I was/am not annoyed, just confused, questions are good!! Manufacturers will often use different transistors in a particular location (i.e. Q3) if they have a stock shortage or an engineering change, but a transistor designated as "Q3" on a particular board, in a particular unit, will...
  11. merlynski

    Pioneer SX-980, Circuit Protection Relay, Random Drop outs

    On the Protection PCB AWM-124, Q2, 2SC1384, is known for this kind of random dropout as it ages. Replace with KSC2690AY.
  12. merlynski

    Pioneer SX-750 Goodwill Special

    There is a 25v cap in parallel with it, if the zener went open, then the cap would get 33v across it. Might then short. That s the +13v supply for the Phono EQ section also.
  13. merlynski

    Pioneer SX-750 Goodwill Special

    19.95 to 22.04 is within +/-5%, Mouser has some in that range . . . Here is one: https://www.mouser.com/ProductDetail/Nexperia/NZX22A133?qs=mSipnS5lFm8HAcDR2FU2KA%3D%3D
  14. merlynski

    Pioneer SX-750 Goodwill Special

    It also goes to pin 33 of the AWE-073 Tuner and AF, and then goes to D13, a 21v zener diode. That is a likely candidate to be shorted (to ground), since R2 tested good.
  15. merlynski

    SX-880 with protection issues

    @mgl99 Help us out and use the appropriate identifier for each component you are referring to, Q3, D4, R16, etc., otherwise we can only guess which component you are referring to. Also the AWR-156 is an SX-980 pcb, this thread is about an SX-880. I am confused by your post #113 . . .
  16. merlynski

    Pioneer SX-750 Goodwill Special

    Pin 21 on the Power Amp pcb AWM-046 is a dc power output to pin 8 on the AWG-046 Tone Control PCB. It powers the whole Tone Control board, no dc voltage there means no audio will pass through the Tone board. Measure DCV on pin 25 of the Power Amp pcb AWM-046. If it is +33vdc then you probably...
  17. merlynski

    Pioneer SX-750 Goodwill Special

    I will put multiple layers of towel between a board I am working on and the rest of the unit, small bungee cords to hold it away from touching the wrong thing, or support the board with a vise or clamp to hold it steady while working on it. I have a lazy susan turntable to hold the unit I am...
  18. merlynski

    Pioneer SX-750 Goodwill Special

    Get a set of these to take measurements: Clip them on, or move them only with the power off. Also get some heat shrink or tape and cover all but the very tip of your regular meter probes, if you have to do some probing with the power on. If the protection relay is pulling in that is good news...
  19. merlynski

    SX-1250 Transistor Question

    The little arrow is always the emitter leg. The arrows direction tells you if it is an NPN or PNP type transistor. Here is a little memory aid I was taught about 50 years ago: NPN is a Not Pointing iN pointer. PNP is a Pointing iN Pointer
  20. merlynski

    Pioneer SX-750 Goodwill Special

    Yes, exactly why I put the (max) after the quoted ratings.
  21. merlynski

    Pioneer SX-750 Goodwill Special

    The 'ballast' resistor in line with Q8 (R29) is not an external heatsink mounted resistor like on the SX-880, and it is already a 5W resistor. I would just add better heatsinking to Q8. Unless you know that Q8 is heating up close to or beyond it rated dissipation level you don't need to change...
  22. merlynski

    SX-1250 Transistor Question

    Instead of thinking about which way it is 'facing', just make sure the legs on the transistor go in the correct holes on the PCB, e.g. base to base, emitter to emitter, collector to collector. The direction it is 'facing' has no electronic significance.
  23. merlynski

    Vintage Pioneer Hifi System Connection Clarifications

    Welcome to Audiokarma! Your Option 1 will work fine if you connect the CT-F9191 deck just like the drawing shows, instead of the R2R, to the Tape 1 loop. Your Option 2 will work if you connect the SX-680 Tape 2 Rec jacks to the SA-7700 Tuner inputs. Tape and Tuner connections are "Line Level"...
  24. merlynski

    Pioneer A-757 relays not clicking

    Reflow the soldering on the Speaker Select switch and other solder joints on ASD1003 board that have not already been resoldered.
  25. merlynski

    Pioneer A-757 relays not clicking

    Does it act the same with Speakers A only, B only and A&B selected?
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