mode "Disc" does not work

[Saint Sinner]

Greetings to all.
I have constructed Bandido. The mode "All metal" works perfectly, but here the mode "Disc" does not work. First of all, I doubt a signal on a receiver exit:




50us/div
TP1 5V/div
TP2 50mV/div




0.1ms/div
TP1 2V/div
TP2 20mV/div




20us/div
TP1 2V/div
TP2 20mV/div


Any ideas?

[Unregistered]

check C15 and the all/disc switch connections.

[Eugene52]

mode "Disc" does not work

Hello , Make sure you check your search-coil RX winding . And see the schematic I posted , Also Check the order of your 100k Disc. potentiometer connections across C9 and C10 !!! You should be able to repair your Bandido , without too many problems...........Regards............Eugene

[Saint Sinner]

Thanks. I will check up.
I also have earthed RX here so:



It is correct?

[Qiaozhi]

Thanks. I will check up.
I also have earthed RX here so:

[ATTACH]6936[/ATTACH]

It is correct?

The ground connection is not needed. There should be a common connection within the Tesoro search head between the TX and RX coils. Adding this extra connection will cause problems.

You should be seeing a 10kHz sine wave at the output of the preamp with an amplitude of approximately 300mV. Have you checked the power supply voltages on the preamp? That would be a good place to start.

[Saint Sinner]

The ground connection is not needed. There should be a common connection within the Tesoro search head between the TX and RX coils. Adding this extra connection will cause problems.

I have made search head independently by the same principle as for Golden Sabre. Grounding RX has made in a search head.
Can be not to earth RX?

You should be seeing a 10kHz sine wave at the output of the preamp with an amplitude of approximately 300mV. Have you checked the power supply voltages on the preamp? That would be a good place to start.

I always aspired to zero. The minimum which I receive is equal 16 mV.
300 mV it is enough?

Pressure of power supplies on preamp +5V/-2.9V.
It is correct?

[Qiaozhi]

I have made search head independently by the same principle as for Golden Sabre. Grounding RX has made in a search head.
Can be not to earth RX?



I always aspired to zero. The minimum which I receive is equal 16 mV.
300 mV it is enough?

Pressure of power supplies on preamp +5V/-2.9V.
It is correct?

The grounding of the RX coil is made via the screened cable. You do not need the extra ground connection that you showed in the previous diagram.
Search through the Tech Forum TGSL posts. There you will find some setup details for the coils, including the correct phase-shift between TX and RX. Because of this required phase-shift you cannot null the coils completely to zero. Otherwise the ground balance and discrimination will not work correctly.
The negative supply seems a little low to me.

[Saint Sinner]

The grounding of the RX coil is made via the screened cable. You do not need the extra ground connection that you showed in the previous diagram.
Search through the Tech Forum TGSL posts. There you will find some setup details for the coils, including the correct phase-shift between TX and RX. Because of this required phase-shift you cannot null the coils completely to zero. Otherwise the ground balance and discrimination will not work correctly.
The negative supply seems a little low to me.

Thanks, Qiaozhi.
Now all is clear to me.
I will check up phases.
I will try to apply 79L05 to reception of lower negative pressure.