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  1. Ylli

    Nikko NT 950 Tuner, no stereo, low level mono output.

    You've got a tough one there. Does the voltages on pins 15 & 16 change with signal or no signal? The voltage you are measuring on TP2 is so far off that I don't think physically tuning the coil will make any difference, particularly since adding a capacitor did not make any difference. You...
  2. Ylli

    Nikko NT 950 Tuner, no stereo, low level mono output.

    There are no test points in the area shown on the schematic, but from the layout it looks like the voltage across R121 is at TP1. Yes, should be zero when properly tuned. The capacitance across R121 would measure about 1uF without the IC installed. With the IC in the circuit, it could measure...
  3. Ylli

    Nikko NT 950 Tuner, no stereo, low level mono output.

    You should be measuring the voltage across R121. The cap goes across R120. I do not see a TP2 on the schematic, where is it? No measurements will make any sense until you put that coil (T102) back in. What do you mean by 50-10pF? Do you mean a 50pf and a 10pf cap in parallel? If so, just...
  4. Ylli

    Nikko NT 950 Tuner, no stereo, low level mono output.

    The test points sregot mentioned are from your Lexman picture. Don't reference that one, it is a bit different than what you are working on. You want to measure the voltage *ACROSS* R121. One meter lead on each side of R121. The voltage on pin 6 is going to be unpredictable if you have...
  5. Ylli

    Nikko NT 950 Tuner, no stereo, low level mono output.

    That 0.9 ohm you are measuring is the DC resistance of the primary coil. I would be concerned if it were much more.... Never seen a shorted internal cap, but have seen a couple open or low value caps. The coils is to detect FM. It can be tuned quite a ways off (with for example a bad...
  6. Ylli

    Nikko NT 950 Tuner, no stereo, low level mono output.

    Leave the original coil as it is, and add an external capacitor across R120. You will likely need to try different values between 33pF and 100pF to find one where the coil tunes properly.
  7. Ylli

    Transistor Substitutions

    Those are both the wrong case. Try the CEN-U07. https://www.digikey.com/en/products/detail/central-semiconductor-corp/CEN-U07-PBFREE/4806927 https://www.mouser.com/ProductDetail/Central-Semiconductor/CEN-U07-PBFREE?qs=u16ybLDytRZ8LEqjL6PxhQ%3D%3D
  8. Ylli

    Yamaha 620 receiver

    The AM audio and FM composite are combined before going into the de-mux chip (IC201), so it could be anything after that point. Temporarily add a short between the negative ends of C223 & C224 (or equivalent points - see schematic). Do you get sound out of both left and right channels? No -...
  9. Ylli

    Voltages are a little off and very distorted sound

    Where do you have +24 instead of +27? I've only got the schematic you posted in your first post as reference.
  10. Ylli

    Voltages are a little off and very distorted sound

    Do you have an oscilloscope? Or an audio signal generator of any sort (looking for 1KHz, 0 - 1 V or so)?
  11. Ylli

    Fixing up a friend’s NAD 7020i

    Do you get the distortion from both channels? If so, it is likely something common between channels such as the power supply. Voltages to check would b the +/- 41 volt rails, +/- 28 volt lines and a (looks like) 43 volt line.
  12. Ylli

    Voltages are a little off and very distorted sound

    Power supply? If you have a scope, might want to check that all the power supply voltages are clean. Without a scope, confirm with your meter that the voltages are stable - switch the meter to an AC range and be sure there is no AC component on the power rails.
  13. Ylli

    Voltages are a little off and very distorted sound

    Yes, that is the same topology. On yours, the second set of 'cascode' connected transistors is just to distribute the dissipation.
  14. Ylli

    Voltages are a little off and very distorted sound

    90 mV across 0.5 ohm resistor is 180 mA. The drop across either transistor is about 17 volts, so each transistor will be dissipating 17 x 0.18 = 3.1 watts. Yes they will get hot. Put them back on the heat sink and see if X11R and X12R still get hotter than X10R & X11R. 180 mA idle current...
  15. Ylli

    Voltages are a little off and very distorted sound

    If that one transistor is not on the heat sink, I'm not surprised if it gets hot. The voltage from the base to emitter of X12R should be the same as the B-E voltage of X10R. The voltage across X12R emitter resistor should be the same as the voltage across X10R's emitter resistor. The voltage...
  16. Ylli

    Rotel RX-400 Distortion Both Channels

    Both channels the same would mean it almost has to be something that is common between the channels. Perhaps the Function or Tape Monitor switch - exercise these a bit and see if they have any effect on the distortion. Confirm both F901 & F902 are good. Measure the voltage on the indicated...
  17. Ylli

    Voltages are a little off and very distorted sound

    Is that 18.4 or 18.7? Germaniums are so variable as to the B-E voltage that it is sometimes hard to tell if the device is good or not from the Vbe. How did you test them?
  18. Ylli

    Voltages are a little off and very distorted sound

    Should see between 0.2 and 0.3 volts across those 'diodes'. X10R and X12R are the actual output transistors. X9R and X11R are bootstrapped to the output to control the collector voltage on the output transistors. Effectively this causes about half the buss voltage to be dropped across each...
  19. Ylli

    Voltages are a little off and very distorted sound

    The bias to X11R/X12R looks a bit high. Double check that you have D3R installed correctly. Measure the voltage *across* D2R and D3R.
  20. Ylli

    Rotel RX-400 Distortion Both Channels

    Are the distortions the same in both channels, or are they a bit different? Do you have a signal source with a line level output?
  21. Ylli

    Rotel RX-400 Distortion Both Channels

    Looking at the left channel, switch 'Func-2R' selects the input. Output of this switch is on it's pin 6. Signal flow shown:
  22. Ylli

    Voltages are a little off and very distorted sound

    What did you replace the output section diodes with?
  23. Ylli

    Technics SA5470 FM stereo issue

    How is the stereo indicator lamp working?
  24. Ylli

    Advent 300 -22vdc fuse blowing

    Trying to determine if it is a hard short somewhere or just something drawing a bit too much current. 5 second blow time would seem like a pretty hard short. When running on the DBT, does the bulb stay bright, or does it dim or go out? How warm does Q401 get? Cold to the touch, warm, hot...
  25. Ylli

    Advent 300 -22vdc fuse blowing

    Was then fuse blowing immediately or after being on for some time?
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