Electronics > Repair
Troubleshooting Noise in Cassette Player Technics RS-M17
dankinzelman:
Thank you. I am traveling for work ATM but I did measure across the tape head (at the plug-in connector to the board). Each channel shows ~210 ohms of DC resistance. Does this sound reasonable?
I will check your other suggestions when I return home, and measure and write down DC voltages at both ICs. As I stated, I did measure them (without taking precise notes) and found all are about 10-12% higher than stated in the service manual, but both channel voltages match each other very well (the same is true for the pins of the Dolby chips).
dankinzelman:
I had already replaced R7. It reads 99.7k. I haven't managed to find the equivalent resistor on the R channel - the R8 stencil on the board is next to the rec-play switch, with no equivalent resistor nearby.
Voltages are pretty much exactly the same between the two chips, within a few millivolts.
Pin 1 2.05V
Pin 2 0.612V
Pin 3 .006V
Pin 4 0V
Pin 5 0.623V
Pin 6 5.838V
Pin 7 10.96V
Continuity from the board to the tape head seems good.
I tried your suggestion and sent a 440hz sine wave into both mic inputs from a signal generator. I've attached a shot of the oscilloscope output from pin 2 of each IC. Top trace is L channel (IC 1), bottom trace is R channel (IC 2), both at 10mV/division. Seems like slight phase shift, assymetric distortion and loss of signal. Could there be a dying capacitor on L channel? How would I identify the faulty component?
Floobydust, it seems like you have one of these, for my personal curiosity can you tell me where on the board R8 is?
wasedadoc:
--- Quote from: dankinzelman on December 05, 2024, 07:29:34 pm ---Thank you. I am traveling for work ATM but I did measure across the tape head (at the plug-in connector to the board). Each channel shows ~210 ohms of DC resistance. Does this sound reasonable?
I will check your other suggestions when I return home, and measure and write down DC voltages at both ICs. As I stated, I did measure them (without taking precise notes) and found all are about 10-12% higher than stated in the service manual, but both channel voltages match each other very well (the same is true for the pins of the Dolby chips).
--- End quote ---
Never measure the resistance of a tape head unless you have a demagnetiser to demagnetise it afterwards.
dankinzelman:
Good to know, thank you. I do have a demagnetizer and will demagnetize. Is there a risk of damaging tapes, or is it more about allowing it to return to maximum performance?
wasedadoc:
--- Quote from: dankinzelman on December 09, 2024, 11:05:02 am ---Good to know, thank you. I do have a demagnetizer and will demagnetize. Is there a risk of damaging tapes, or is it more about allowing it to return to maximum performance?
--- End quote ---
A magnetised head gives higher replay noise and slightly erases existing recording each replay.
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