Hi!
I have this problem with my Nad amplifier. Yesterday the amplifier was in standby mode and i observed that it's starting to make relay clicks constantly. The relay clicks repeated in 2 seconds interval, the amber power led it's no longer lit, the power button not responding. Disassembling the amplifier i found that the clicking relay is the one on the volume and tone board. Measuring the 5v rail on main board i get 0.4v ascending to 1.8-2v synchronized with the relay clicks. If i disconnect the power supply board from the main board, i get stable 5v on power supply board. Any idea how to find the bad components? Thanks!
I have this problem with my Nad amplifier. Yesterday the amplifier was in standby mode and i observed that it's starting to make relay clicks constantly. The relay clicks repeated in 2 seconds interval, the amber power led it's no longer lit, the power button not responding. Disassembling the amplifier i found that the clicking relay is the one on the volume and tone board. Measuring the 5v rail on main board i get 0.4v ascending to 1.8-2v synchronized with the relay clicks. If i disconnect the power supply board from the main board, i get stable 5v on power supply board. Any idea how to find the bad components? Thanks!
Thanks MarsBravo. I will test test diode. In the meantime i did another verifications. Here is a cable that came from the key circuit and go in the CB34 connector on the main board. If i pull off this cable from the main board i get stable 5v, +-12v, +-18v and so on the other rails, on the front panel all leds is lit, except the power led. With the cable connected i get the same instable voltage on the 5v rail, and 0v on the other rails. As i can see on the diagram, pin8 of the CB34 connector is related to protection.
Attachments
Yes, i desoldered the two smd diodes, i measured 0.6v, reverse measure is open circuit. The two desoldered capacitors was measured in resistance mode. The capacitors charging, then discharging in DC mode. I try to measure the other components, maybe i find the defective one. Thanks for your help!
please replace the volume control motor transistors (2nos) next to motor on the tonecontrol board
Hi, I had the same issue and there is no short on the front panel.
By unplugging the front panel you disconnect the Standby-Pull-up resistor. This then causes the Standby-Relay RL51 (also powered by 5V) to enable and switch on the transformer. This relay causes a current draw of around 100mA from the 5V Standby supply. Due to the primary clamping diode on the power supply board D536, type: P6KE200A being bad, the power supply shuts it self off when there is very little load on it. Basically it runs fine when the Stand-Relay is enabled and drawing current, but the diode D536 is getting really hot, to a point off smelling it. This diode somehow did not fail in short-circuit but rather got a reverse forward voltage of 0.7V. So try changing it, if the 5V supply switches it self of repeatedly.
I hope I could help.
By unplugging the front panel you disconnect the Standby-Pull-up resistor. This then causes the Standby-Relay RL51 (also powered by 5V) to enable and switch on the transformer. This relay causes a current draw of around 100mA from the 5V Standby supply. Due to the primary clamping diode on the power supply board D536, type: P6KE200A being bad, the power supply shuts it self off when there is very little load on it. Basically it runs fine when the Stand-Relay is enabled and drawing current, but the diode D536 is getting really hot, to a point off smelling it. This diode somehow did not fail in short-circuit but rather got a reverse forward voltage of 0.7V. So try changing it, if the 5V supply switches it self of repeatedly.
I hope I could help.