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
Then there is a shorting of the 5V rail on this board (and not on the ToneVol board, which respons to the failing 5V only).
There's quite a lot connected to the 5V rail on this Key board... I've a look at it.
There's quite a lot connected to the 5V rail on this Key board... I've a look at it.
...seems to be fine... Sure?
Just lift one leg out of the board of them (1 by 1), it won't harm the rest.
Otherwise something else is shorting, think of small unpolarized caps and then the semi's.
Just lift one leg out of the board of them (1 by 1), it won't harm the rest.
Otherwise something else is shorting, think of small unpolarized caps and then the semi's.
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!
I have some news. I separated the front panel from the main board and powered up with 5v. The power led start to lit in amber(standby mode), pushing the power button i have blue power led, so i think the front panel is good, i have to search for problems on the main board.
what was the outcome
Hi Claark what was the outcome of this investigation? I have the identical problem.
Hi Claark what was the outcome of this investigation? I have the identical problem.
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.