Denon DRA-435R shuts off the speakers output

[BrassTeacher]

Across the speaker relay coil, there should be an electrolytic capacitor. Replace it. If there are two speaker relays, replace the cap across both's coils. Make sure to get the polarity correct, or the cap will turn itself inside out pretty quickly. There should also be a diode across each coil, test them to make sure they are ok as well (They probably will be)

 

[ve ze]

Across the speaker relay coil, there should be an electrolytic capacitor. Replace it. If there are two speaker relays, replace the cap across both's coils. Make sure to get the polarity correct, or the cap will turn itself inside out pretty quickly. There should also be a diode across each coil, test them to make sure they are ok as well (They probably will be)

The speaker relay is RL401 on these images below. When you say electrolytic capacitor across the relay, could you pls point to that one from the images?

 

[BrassTeacher]

The schematic and the board photo indicate that it does not have a capacitor across the coil. Odd. The usual arrangement is this:
(Stolen from DIY Audio)



When C1 wears out, and starts leaking current, the relay won't have enough current to stay closed.

But, since we have the schematic, ZD401, R408, R451, R433, and TR408 are the relay driver circuit. The first thing I would check is TR408. When the relay drops out, touch the top of the transistor to see how hot it is. If you'd rather not do that, once the relay drops out, hit the transistor with a blast of free spray to see if the relay comes back on (If it were me, I would do this anyway if the transistor felt hot). If you don't have freeze spray, a very quick burst from an inverted electronic duster can will work. If the relay does come back on, replace TR408 and you should be done. But, to be thorough, check R451 and R433 while the transistor is off the board. If they have drifted to lower resistance, the will overheat the transistor, and if they have drifted towards higher resistance, the transistor may not be able to provide enough current to keep the relay closed, especially after the circuit warms up. If the relay stays out, check ZD401. If you don't have the equipment to check the zener diode (A DMM and a variable power supply capable of exceeding the Zener's voltage), just go ahead and replace it with the exact part, or one rated the same Wattage and Voltage. They are cheap.

 

[ve ze]

The first thing I would check is TR408. When the relay drops out, touch the top of the transistor to see how hot it is. If you'd rather not do that, once the relay drops out, hit the transistor with a blast of free spray to see if the relay comes back on (If it were me, I would do this anyway if the transistor felt hot). If you don't have freeze spray, a very quick burst from an inverted electronic duster can will work. If the relay does come back on, replace TR408 and you should be done.

Following your advise I did check the transistor TR408. The contacts are solid, the temperature is not running high, just normal range between room temp and ~ 80F. When the relay opened the connection I used cool air on it. It didn't change anything The relay still stayed open. And it immediately closes upon power cycling on the unit.
Could that be that the protective circuit does its job correctly, and there is actually a spike of DC current on the speaker feed. What could that be caused by? Is there a way to find out?

 

[BrassTeacher]

Yes, perhaps two ways. Could you post a closeup of the schematic showing the protection circuit?

 

[ve ze]

Yes, perhaps two ways. Could you post a closeup of the schematic showing the protection circuit?

Yes. Here it is.

 

[ve ze]

Hi Don, do you think you can take a look at the image below? I wonder if the faulty thyristor (SC401) may be the reason the protective circuit is breaking the connection to the speakers?
thanks for your assistance.

 

[ctirwin67]

All, I'm having this exact same issue. The protective circuit is breaking the connection to the speakers randomly. It happens usually after somewhere in the 5 to 10 seconds range, but other times it will go for a minute or two, up to an hour before breaking the connection. If I turn off the unit and turn it right back on, it does the same thing again. I resoldered TR408 as per above but no change. And TR408 is not overheating. Based on the fact that it happens randomly and will work again as soon as I power the unit on and back off again, it wouldn't seem to be related to circuit warmup. Any other thoughts?

 

[TheFireman]

All, I'm having this exact same issue. The protective circuit is breaking the connection to the speakers randomly. It happens usually after somewhere in the 5 to 10 seconds range, but other times it will go for a minute or two, up to an hour before breaking the connection. If I turn off the unit and turn it right back on, it does the same thing again. I resoldered TR408 as per above but no change. And TR408 is not overheating. Based on the fact that it happens randomly and will work again as soon as I power the unit on and back off again, it wouldn't seem to be related to circuit warmup. Any other thoughts?

I'm having a similar issue with mine. The audio is scratchy/intermittent (when it works at all) and no amount of potentiometer cleaning has done the trick. I'm thinking it's something electrical on the power supply or relay board, but have no idea where to start. If anyone could help it would be greatly appreciated.