When turning on and after waiting few secs for the delay circuit, then a reassuring click emanates from the output relay if all is well. Qa is the relay coil's driver transistor. Qa BC550C should show healthy Vbe, Za Zener should show 9.1V across its legs, Dd flyback diode should show the coil's working voltage across its legs. Somewhere around the nominal 12V. With enough +/-V margin, no problem.
That's what I am hoping! Now, is the relay defective, or is it part of something that senses something is wrong and wont allow it to turn on?If the relay doesn't work for some reason it surely cuts the signal output route when at rest. Your DMM could be just measuring noise in this case (?)
Dd diode is for fly-back voltage control on the relay's coil. If all is well it should be showing 10V or more across its legs. Its the same as on the coil because in parallel. Red probe on its cathode for correct polarityOr is diode dead...better check orientation.
diode behind relay...................................................1.3 volts a/cIf the three Leds don't shine, one or more could be wrongly oriented or broken. Cutting off the power line to the relay circuit.
The three leds are lit up fine. I have better measurements now, dont know if they are good, but here they are:
Qa....................................................................................3 mV
Za....................................................................................4.3
Then maybe it does work? I dont hear it, but everything lights up that is supposed to light upThe three Leds normally shine after the turn on delay right at the moment when the relay should also click.
when not selected, I measure 0 across diodes. As they are switched on, 12 volts, and it moves as I switch. It must be selected to showthe12 volts.Do you get good dc voltage across the selected input's relay diode on I-select?
no flyback diode only measures 1.3 volts. The diodes on the I-select measure 12 volts, once they are switched to, otherwise they measure zero.When turning on and after waiting few secs for the delay circuit, then a reassuring click emanates from the output relay if all is well. Qa is the relay coil's driver transistor. Qa BC550C should show healthy Vbe, Za Zener should show 9.1V across its legs, Dd flyback diode should show the coil's working voltage across its legs. Somewhere around the nominal 12V. With enough +/-V margin, no problem.
Dd diode is for fly-back voltage control on the relay's coil. If all is well it should be showing 10V or more across its legs. Its the same as on the coil because in parallel. Red probe on its cathode for correct polarit
not sure what you want me to measure here? There is a 3.3k resistor there. It indeed measures correctly.Also check that between IN and J1's gate pin there is 3.3K R1 bridging value to be measured and not some broken line or pad interruption. Ohms you measure with power off only.
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