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  1. MAV

    Tuning indicator Pioneer SX-838

    Thanks for all the tips. The Pioneer SX 838 i bought appears to be unopened original. I will try to clean and deoxidize before starting to adjust or similar. /Greetings Mathias
  2. MAV

    Tuning indicator Pioneer SX-838

    Hello I have a Pioneer SX-838 and I have a question about the FM tuning pointer not showing quite right from half the FM scale. The tuning pointer seems to show correctly from 88 Mhz-101.9 Mhz but then up the scale from 101,9 Mhz (display show 102,3 Mhz) the pointer shows something wrong up to...
  3. MAV

    What's Pioneer in your rig?

    This is what I have right now. Pioneer SX-939 (uses as Preamplifier) Pioneer PL-51A (ortofon 2M Bronze) Pioneer CT-F9191 Pioneer SE-50 ACURUS A250 (uses as Power amplifier) TEAC A-3340S SONY SCD-XA9000ES CANTON RC-L
  4. MAV

    Signal strength meter?

    Thank you for the advice. Then I have a small job to do on Halloween weekend
  5. MAV

    Signal strength meter?

    Hello I have a Pioneer SX-939 in good condition but the FM signal strength meter (the meter on the left side) turns on sometimes after 30s. could it be some component that controls the function that is defective or have any idea what might be causing this?
  6. MAV

    Vinhage hi-fi

    Vinhage hi-fi
  7. MAV

    What are you Listening To Right Now? - and more

    Gordon Lightfoot Reel to Rreel Qadraphonic
  8. MAV

    Hung Chang 5506 manual?

    I have a fully functioning oscilloscope Hung Chang 5506 and I am looking for this manually. Does anyone have a copy or can you suggest where to find it on the internet? / Mathias
  9. MAV

    High voltage driver Transistor, STV4H?

    Now I am completely finished with my completely renovated Pioneer SX-939. I have completely renovated (new circuit boards Power Supply and Power Amplifier etc, etc.) my Pioneer SX-939 and i measure the outputs after the last adjustment of Bias (25mV) and DC Offset 0V. The probe is set to 10X...
  10. MAV

    Pioneer SX-939 protect relay shuts off with volume increase (pict)

    Hi. And thanks for the tips mr markthefixer. Finally found the root cause of the protection relay cuts when increasing the volume. The transistors 2SC869 in the protection circuit which have a different leg configuration than KSC1845. So now KSC1845 is sitting right in place right facing. Found...
  11. MAV

    DC Offset?

    Ok, thanx mr markthefixer
  12. MAV

    DC Offset?

    Hi. I have some thoughts about where to check DC Offset. Most service manuals state that you must check and adjust the DC offset on the Amplifier board at measuring points. It must be better to measure direct at the output terminals because then you measure after Protection curcuit and...
  13. MAV

    High voltage driver Transistor, STV4H?

    I found problem, bad soldering Base Q8,,no electric contact. After new soldering Base Q8 now protection relay click and i can adjust Dc Offset to approx 0 mV output 25 and 10. I have made brand new circuit board Power Amp and Power Supply and all components are new but one little bad...
  14. MAV

    High voltage driver Transistor, STV4H?

    I have made a few more measurements. Across capacitor C6 is + 10.5V and capacitor C5 22mV. Q4 Base and Emitter 25mV and Base and chassis ground 10V.
  15. MAV

    High voltage driver Transistor, STV4H?

    Okay, I have checked KSA992 (Q1-Q4) and they are E / C / B and the original 2SA726S are B / C / E. Emitter sits together Q2 and Q4. So it looks right.
  16. MAV

    High voltage driver Transistor, STV4H?

    Here are some approximate measurement numbers. I have no test yet to replace the D5 and D6 Pre stage drive Transistor KSA992FBU (PNP) Q1, E = 0.7V, C = 42V, B = 0.15V Q3, E = 0.15V, C = 42V, B = 0.9V Q2, E = 1.5V, C = 39V, B = 0.9V Q4, E = 1.5V, C = 43V, B = 10.0V Varistor D5, + 2.3V (across)...
  17. MAV

    High voltage driver Transistor, STV4H?

    I have also checked DC Offset on outputs 10 and 25. On output (25) there is +25 VDC and output (10) +0.6 VDC. DC Offset cannot be adjusted with the trim potentiometers. I will check this STV4H and test as you described in the post. Thanks for the tips!
  18. MAV

    High voltage driver Transistor, STV4H?

    I measure +/- 43 VDC on the collector points Q5-Q8 where it should be +/- 1.2V. Is the varistor STV4H faulty? Emitter and Base voltage is ok. Voltage from Power Supply is ok. All components are new. (all output transistors Q1-Q8 is disconnected)
  19. MAV

    No bias SX-939?

    Now only the fun is left. Solder all new components and new cables on AWH-030 :) And here is new Power Supply AWR-056
  20. MAV

    No bias SX-939?

    yes, I'll think about it, thanks for the tip,
  21. MAV

    No bias SX-939?

    Here is the solution to many problems with Power Amplifier. I made a new circuit board :)
  22. MAV

    No bias SX-939?

    I have found one fault, a copper trece/path on the back was broken to pin 32 (I should make a new PCB AWH-030) ,,so now can i set bias rigth channel,, Left channel still 0V bias, must check this also. The copper traces is so thin that you do not even feel with your fingers, fantastic that they...
  23. MAV

    No bias SX-939?

    okay i'll look at that Left channel resistors R47, 49, 39, 43, 45, 37 = 0 V Rigth channel resistors R48 -0,7 V R50 -0,02 V R40 -0,16 V R44 -0,4 V R46 -0,4 V R38 -0,4 V
  24. MAV

    No bias SX-939?

    Left channel Here are the measurements on transistors Q5-Q11 Q5 - Q7, C-C / 2.78 V Q9 - Q11, E-E / 2.39 Q9 - Q11, B-B / 2.79 V Q9 - Q11, C-C / 101 V Rigth channel Here are the measurements on transistors Q6-Q12 Q6 - Q8, C-C / 2.3 V Q10 - Q12, E-E / 1.15 V Q10 - Q12, B-B / 2.3 V Q10 - Q12, C-C /...
  25. MAV

    No bias SX-939?

    Now i am back. Here are the first measurements on transistors Q5-Q11 Q5 - Q7, C-C / 2.78 V Q9 - Q11, E-E / 2.39 Q9 - Q11, B-B / 2.79 V Q9 - Q11, C-C / 101 V Output R43, R45, R47, R49 approx 3 mV p.s Power Supply voltage is +/- 51V, no speaker or dummy resistor connected These are the...
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