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Strange Resistor network, how to identify its topology

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--- Quote from: tooki on October 02, 2021, 02:42:49 pm ---
--- Quote from: hitech95 on October 02, 2021, 09:53:28 am ---
--- Quote from: tooki on October 01, 2021, 06:25:36 pm ---Do you mean you’re having trouble identifying the audio in and out signals from the tape deck? Or are you asking something different?

--- End quote ---

Playback and Audio signals are on pin 1,2 (rec) and 4,5 (playback) of CN1304.
I dont understand what Pin 9 and 10 on CN1303 are for. I think it is to enable the erase head and to apply the bias or something to the playback head.
Watching Q1305 Q1303 it sems that thoose are simple digital signals.

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I'm not certain either. It seems very likely that REC enables the bias signal (used both for the record head and the erase head). BP seems to refer to something called "Beat Proof", but I have no idea what that is*. If you follow the outputs of those two transistors, they go to 1) what must be the bias oscillator, plus the switch (IC1000) that enables bias, and 2) the beat proof level switch (Q1317) that does… something.

It should be easy enough to observe the REC and BP signals to see when they're enabled. I'd just make sure to test (at minimum) in both playback  and record, with regular and chrome tapes. My guess, based on the info below, is that the BP line is controlled (via the MCU) by a setting on the radio tuner, and that if one is not recording from AM radio, that its position is completely irrelevant.

*Googling "cassette beat proof" led me to some Panasonic manuals, like one for the RQA-160 portable cassette recorder, which has Beat Proof on a mode knob. It says on page 12:

--- Quote ---Beat proof switch
When an AM broadcast is recorded, the beat proof switch can be used to reduce unwanted "beat" signals. Set the switch to whichever position that gives you the best results. A "beat" signal normally sounds like a whistle.
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Unfortunatly the unit was flooded and the only part that was fine is the deck. So I have no original circuit to test it out and mimic the original signals.

Unless you plan to record from AM radio, it sounds like you can ignore the BP line. I’d probably just tie it high or low to keep it stable.

The bias signal will definitely be needed during recording.


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