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  1. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    There is something wrong with the last measurements. Grey to Grey (Transformer Side) = 05.5 Grey #1 to Green (Transformer Side = 05.5 Grey #2 to Green (Transformer Side) = 05.6 The Grey to Grey(Transformer Side) should be the sum of the greys to green. i.e should be about 11.1 Could you...
  2. dorke

    How to build a 455khz oscillator for a signal generator..

    Hop, What are those strange "RF connectors " ? never seen them before. That EICO can still be used for alignment of "Hi-FI" receivers in it's "A BAND"
  3. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    The new schematics scans are workable,thanks. Before we continue, I forgot to ask an important question: How good are you at soldering?What equipment do you have? Can you please show a soldering work you did and a photo of your equipment. Good soldering is essential to the repair, if done...
  4. dorke

    Cheapest way to get data from multiple(100s) of sensors?

    Bob, That would be 20 outputs. (Tristate capable or with an extra external NPN transistor). Steve, The purpose of the ULN is to be able to drive a single row of LEDs at the same time with the required current -about 200mA ,all sensors of that row require about 20mA max. Take care not to drive...
  5. dorke

    Amp In Protection Mode

    Hi Rick, You have the protection LED on? You should start with measuring the DC voltages on IC701 (TA7317-protection IC). It is a 9pin SIP package. DCV relative to GND (pin-4 of the IC or the chassis or the black(-) terminal of the speakers whichever is easiest) The schematics show the normal...
  6. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    The DC resistance is rather low ,but probably is ok. that means the primary of the transformer is probably o.k. The schematics are barley readable. It would be easier if you can scan them in a higher resolution. Please open and remove the bottom plate. And a photo please. Is it easy to...
  7. dorke

    Help with Cassette Dolby circuit debug

    You do need a scope to get to the bottom of this. What is the load your "tester" puts into the circuit? Maybe it is too small and caused damage? I think it isn't wise poking around with it. Crackles may be produced by bad caps or even a combination of dirt and corrosion . How clean is the...
  8. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    Zero like 0.0 ohm ? Did you check it in the 200 ohm DMM range ? Put the voltage selector at 220V and re-measure resistance between the power cord pins. What do you read? Could you please scan/photo (in readable quality) and post the schematics. At least the one that shows the Fuse F1.
  9. dorke

    Help with Cassette Dolby circuit debug

    Different audio levels play a roll in the way the Dolby IC performs. Can you lower the audio volume at pin 3 of the left bad channel by adjusting the PB trimmer (VR1) to, any effect /improvement? Before you do, mark the trimmer position.
  10. dorke

    Help with Cassette Dolby circuit debug

    I meant, the same levels between left and right channels on pins 5, 2 and 3.
  11. dorke

    Help with Cassette Dolby circuit debug

    I couldn't find the "B" part datasheet either. The 645 is a direct replacement/ pin compatible with the 645B,the datasheet states that clearly. Are the audio levels the same at pins 5,2 and 3? If you look at the LM1112(page 1-121) you can see that bursts can occur in the IC operation at pin 7...
  12. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    It is just a transformer,not the hole power supply. They are specially build with special requirements(like voltages ,amperage , shielding etc. ) and very unique to a brand and usually to a model as well. It is by far the most expansive single element in a receiver/amp. That one would probably...
  13. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    The build quality shows. I wouldn't jump into any conclusions about the source of the fault. If you are willing to spend the 12$ to buy the service manual(and post it here for us to see and analyze), myself and others here will help and guide you with the repair. The "big black box" is the...
  14. dorke

    Help with Cassette Dolby circuit debug

    The datasheet you posted is of the NE645 not the NE645B they are slightly different. The info in the datasheet is minimal and enigmatic. Look up the datasheet of the NE545 (an older Dolby IC) and the LM1112 (an improved version), they both are pin compatible but slightly different and have a...
  15. dorke

    How to work with RS485 ?

    Sorry, But no Nirvana for you, only toil,tears and sweat.;) Google it, and learn the hard way ,no way around it!
  16. dorke

    Voltage Divider vs Series Resistor

    Driving DC motors(or any high current/high wattage element) with resistive series (wasting) elemnts is not a good idea. It shouldn't be done in both ways.
  17. dorke

    Help with Cassette Dolby circuit debug

    The first thing that stands out is the different Vref voltage at pin 4. It should be about 18.6/2=9.3v achieved by the voltage divider of R151 and R153 each 1k and filtered with C151. Are you sure of bad/good, left/right on the pin voltages columns? looks the other way around regarding Vref.
  18. dorke

    Voltage Divider vs Series Resistor

    What you are describing as "series resistor before a load" is basically a voltage divider. But, What is the load? If it is a fixed value resistor, then it is a voltage divider with a known voltage on the load(the same as 2 resistors). If however ,the load value is not fixed (like in many...
  19. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    Welcome to EP. The SA-828 is 1981, not the 70's. It is an excellent stereo receiver and probably is worth fixing, unless the transformer is blown. "Whaddya think my chances are?? " That will depend on your knowledge and experience, do you have any? You should have a service manual or at least...
  20. dorke

    Cheapest way to get data from multiple(100s) of sensors?

    Are you joking or what?o_O
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