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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 21st Sep 2021, 7:07 pm   #1
AlanC
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Default Technics RS-B48R cassette deck- lights on, nobody home

Hi all,

This unit has not been powered for a very long time and was stored in the owners attic. It was apparently working when stored away. In view of the long time without power I did basic safety checks on it before bringing it up on a dim bulb tester.

The fault is that when powered on, the VFD level meter lights up, as does the forward transport direction indicator (it is an auto reverse machine) but it is completely unresponsive to any of the function keys. When you insert a cassette the capstan motor runs, this is controlled directly by a simple switch in the transport. I have the service manual for it.

The power rails are all up and very close to the values shown on the diagram. The microcontroller chip signals are shown in the manual for each pin; it has 5v power on pin 39 as it should, the clock on pin 40 is very close to the waveform shown in the manual. Since the clock is set by an external RC network, the oscillator must be in the chip and is clearly working. The reset is clean and rises to the full 5 volts.

However the keyboard scan outputs on pins 31 to 35, which should go high in turn with a 2mS pulse every 11mS, are all stuck high at 5V. Disconnecting the keyboard connector does not change this.

It looks to me like the chip is faulty, but is there anything else I should check before I condemn the machine? - I assume the processor would be unobtainable by now. I can post a screenshot of the relevant parts of the circuit if it helps.

Thanks, Alan.
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Old 21st Sep 2021, 8:07 pm   #2
Nickthedentist
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Default Re: Technics RS-B48R cassette deck- lights on, nobody home

Presume the timer switch is in its central position?
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Old 21st Sep 2021, 8:35 pm   #3
AlanC
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Default Re: Technics RS-B48R cassette deck- lights on, nobody home

Quote:
Presume the timer switch is in its central position?
Thanks, it is indeed.
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Old 21st Sep 2021, 10:17 pm   #4
ben
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Default Re: Technics RS-B48R cassette deck- lights on, nobody home

Dirty cass-in leaf switch. Had this before. Try bridging the contacts and see if the transport works. There may be more than one switch to 'fool'.
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Old 22nd Sep 2021, 5:33 am   #5
Nickthedentist
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Default Re: Technics RS-B48R cassette deck- lights on, nobody home

Good point. There will be several leaf switches like this. Clean their contacts with thin card moistened with Servisol, and remove the PCB mounted ones and clean their legs and the pads on which they sit with a cotton bud.
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Old 22nd Sep 2021, 6:44 am   #6
AlanC
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Default Re: Technics RS-B48R cassette deck- lights on, nobody home

Thanks Ben and Nick will do.
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