Salas DCG3 preamp (line & headphone)

Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
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.
 

Russellc

Member
Paid Member
2003-03-06 12:59 am
midwest
If 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:
diode behind relay...................................................1.3 volts a/c
Qa....................................................................................3 mV
Za....................................................................................4.3
 

Russellc

Member
Paid Member
2003-03-06 12:59 am
midwest
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.
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.
 

Russellc

Member
Paid Member
2003-03-06 12:59 am
midwest
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

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.
not sure what you want me to measure here? There is a 3.3k resistor there. It indeed measures correctly.