DENON AVR REPAIRED

 Is DENON AVR Model X-500 Prone To Fungus Attacks And Rusting

Those of you who have read my previous articles on servicing same model might know the reason for my question. For those who have not, here

I received the same model from a different customer living in my home town with the complaint that it just blinks after switching on, which the customer also knew was a protection mode.

I am only giving the image of the model number plate, to show that it is a different set with a different serial number. I am skipping insertion of other images of inside as it will be a repetition.

After dismantling the whole set and subjecting it to thorough cleaning of every part, I took up the remote control for rectification, as it had rusted battery contact springs:

I had to clean the area thoroughly and literally dig out the rusted broken spring from its groove. After replacing the spring and putting the battery, and also replacing the capacitor on it, the remote did not work, even though I had cleaned all the contacts too using IPA. Then I replaced the crystal, upon which the remote started working very well.

Why did I take up this first? Because, controlling the system through manual mode was very difficult, when sets are dismantled and connected externally for check-up. As the display was dim, I dismantled the front panel and was not surprised to see the condition inside:  

    

I cleaned the board thoroughly using IPA. Removed the display and cleaned the legs carefully, as the pins were very thin and likely to break, and replaced all the electrolytic capacitors on this board. Then when I tested, the display was found very healthy and responded to dim commands.

After providing extension wires and connecting the amplifier board externally like how I did in the case (3) link given above, I applied power and saw the serial bulb lighting up indicating high current drawn. I switched off and discharged the tank capacitors and looked for the trouble maker. When I checked the output transistors of the amplifier one by one, I saw two transistors short in one channel. So, I removed them. Still the short was present. (Short between ground and + rail) Then traced it to its speaker protection relay, which was dead short between one pole and one way! I have never seen a relay shorting like this before in my whole years’ experience!

Replaced the transistors and relay after checking every part in that area for any short or open and reconnected the board externally and applied power. This time there was no problem and it worked well. The probable cause for failure was leaky transistor which might have drawn high current shorting the relay. That’s how we also got a thermal error, as the transistor might have been exceeding the temperature limit. Anyhow, I let the set run for several hours before closing it.

You can have a look at the number of pages printed to study the circuit diagrams for easy trouble shooting and the number of minimum components that were replaced in the set, due to the fact that the customer did not have a large budget for the service. 

Anyhow, I fit the set back and delivered it to the customer, after he saw its full functions at my home.

He was so happy to get the set back to working condition. Mission accomplished with great satisfaction getting added to the collection!