Electronic-Nulled Loops

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I am suspicious about cd4051 in this circuit. There is multiplexing for sure but maybe there is just clever use of ordinary 4053 chip. What do you think?

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Schematic update.

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I just now realized that there is a CD4024 chip on main board. CK wire goes to pin 3 of CD4024. Now I think everything is closer to being solved.
I compare the 2b board with the 2ba board. On the 2b board nothing is connected to pin 3 of CD4024. So this question is put to rest.

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From this picture it looked like CK(white wire with purple stripe)is going through the hole in the main board. To the top side.

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Or do you mean from 6 and 2 of 393 at the end of the filters section.
why would it connect there?

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Main board lm393 pin 2 or pin 6. Those are the disc and ground balance phase shifters taking signal from the Tx oscillator waveform. So CK could mean the Tx clock?

[Mario-j23]

There are two power sources +12V from Dmc and +5V (probably) from the stabilizer on the autotune board, which is not taken into account in your diagram. It seems to me that CK can take the signal from lm393 pin 2 and pin 6 where there is 0V on the nautilus board.

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Schematic. Now I hope I am a bit closer.

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555 configured as one shot monostable pulse generator. I should have looked more closely at your pcb layout. So pushing the slb switch merely triggers a pulse which enables the electronic potentiometers to do their thing. The pulse should be long duration maybe 3 seconds or so, after which the digital pots are disabled. Maybe that's how it works.

[Mario-j23]

I discovered one more ERROR. In the forum posts about DMC IIb there is information that the inductance of the Rx coil = 8.42mH (FAKE). correctly RX=5.42mH. My colleague YOYO27983 also made a mistake by replacing Tx with Rx in the DMC VLF diagram (correctly Tx = 2.5mH, C1 = 47nf, C2 = 470nF, F = 15.39kHz, RX = 10.7mh, C = 10n, F = 15.38Khz ) I am one step away from starting Nautilus, I still need to connect the coil socket. Does anyone have a photo of the eight-pin DMC IIB coil socket connector from the printing side? I will be grateful for your tips. Greetings and wish you a healthy and happy Christmas.

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Yes. You are absolutely correct.

[Mario-j23]

Yes, this path is the output from the voltage regulator, probably +5v
Connection to US 555 pin 2 and 6 is not possible! Look at my PCB and the red upper trace.
The connection will cut the +5v and GND lines! Something doesn't feel right here.

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Good job, nice and clean diagram. There is still no +5v connection to which pin of the 4051 system does this path go?

Seems I was wrong, it looks very much like this track is output of voltage regulator. I will have to correct my schematic again.

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Looks good. Do you know how the opamps and comparators are connected to the power supply?

I forgot to put those didn't I.

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That's good to know. The 4051 has vdd (12v), vcc digital ground(?) and -vee or analog minus(B-)?

It's important we know the power connections for the digital pots.

For this circuit, the photos show pin 6(inhibit/enable) pin 7(Vee) and pin 8(Vss) are all connected to ground.(4051 chip)
The datasheet has some interesting things to say about setting the Vee.