Multi Kruzer Transmit problem

[reiv]

Hello, does anyone have a diagram of the Tx transmitter for the Multi Kruzer?

The device only works properly at a frequency of 5 kHz. The remaining 14 and 19 kHz have negligible sensitivity, phase detuning (silver reading 60) and no ferrite tuning.

I measured the amplitude of the Tx transmitter with a multimeter:
5 kHz - 5.81 V (AC) (giving approximately 18 Vpp)
14 kHz - 3 V (AC) (giving approximately 9 Vpp)
20 kHz - 1.77 V (AC) (giving approximately 5.5 Vpp)

I think that 14 and 20 kHz have too small amplitude. I checked the relay, transistor Q2, the U12 switch is ok, I'm thinking about U9 (74HC595D), but without a diagram is difficult...

[ivconic]

I assume that those relays in combination with C66-C68 overlap when selecting frequencies.
I would start my investigation from there. I would also consider checking U12 and Q2.

[reiv]

Thank You for answer Ivconic. Yes relays nr 1 and 2 with those parrael caps are for changin Tx circut they are driven by U9 (74HC595D) and Relay nr 3 is for changing circut for Rx signal. I did earlier what You suggest desolder them and check, U12 is analog switch (TS5A3159) and Q2 double BC807 (BC807DS). I`m not sure is this transistor is main transistor in Tx circut, without schematic is difficult to track.. Relay connections with different freq. looks like this:

[pito]

BC807 can be a complementary pair Tx output, check emitters of them , do they are connected together ?


I measured the amplitude of the Tx transmitter with a multimeter: = not good, multimeter is ok for 50 or 60 HZ not for kHz, you need oscilloscope or any coil with LED as a field strength meter.

[Carl-NC]

Most multimeters are only designed for measuring low frequency AC volts. The decrease you see might be the roll-off of the multimeter, you need to check with an oscope.

[ivconic]

Pito and Carl are right, they already answered you.
As for "problems"... sometimes (rarely) a very trivial thing happens; the contacts on the relay are not good and by overlapping they make a "crazy combination".
The relay cannot be directly controlled from "logic" but must have a "driver". Transistor or fet. Go "backward" from the relay and find what "drives" the relay.

[reiv]

Finally found it... (of course You were right about multimeter). Film capacitor C4 was busted (0.67nF, it should be around 150nF), I bet it was because of previous "repair guy" and his hot air gun, when he change pin socet on PCB... Thank You for all support

[ivconic]