Third Visit Of Complaint Monger DENON AVR-X500
Those of you who have read my previous articles on this same model might know the history of the set. I am providing the links below to refresh:
This set was reported to be having the same ‘protection mode’ problem somewhere in middle of 2022 and I requested the customer to take it to another known technician within the town, who had recently returned from Gulf and started a shop and was known to be good through another customer of mine. I did this as I was loaded with a lot of TVs and I was doing the up and down trips to bring it down. I also sent the service manual and offered help to that technician. Unfortunately, he could not do it and finally the customer took it back after a few months and requested me to look into. I put him on hold and finally I called for the set in March, 2023 when he reminded about it. I am sad to say that many of the screws on the cabinet as well as inside were missing! This is the last thing one should do, especially when you are returning the set to a customer. I have the habit of putting new screws whenever I find one missing. I hate to see a set without its fixing screws! Having said this much, let me narrate the present story of what I found inside the set this time and what all I did to resolve the problems.
On applying power, I found that the display was very dim and even after selecting the brightness setting modes, it did not respond. So, I removed the front panel and you can look at the kind of fungus and rust formations inside:
After cleaning the legs taking due care not to break it and cleaning the board also thoroughly, I put the display back. I also replaced the rusted transistor. Then when I connected it back and applied power, got a good and healthy display:
Pressed the Channel + and Status buttons on the panel simultaneously and read the error code recorded. It was showing Thermal Protect A. ‘A’ represents the right channel of the audio output and ‘B’ the left. As this set seems to be in the habit of visiting me often, I decided to extend all the interconnecting wires so that I can keep the Amplifier board separately for easy trouble shooting. I provided a long strip wire. I cut the other inter connecting wires, stripped the ends and cleaned it and joined them tightly twisting it with a nose player. Soldered the open ends of the cut wires to the pins in male connectors. Each wire was protected with sleeves to prevent accidental shorting. Then provided jumper wires with female connectors at both ends and joined these together tightly. Following pictures would help you follow my explanations:
I connected thick electric wires to extend the secondary AC outputs of the main transformer for providing power supply to the board. I had sprayed IPA on the board followed by CRC 2-26 to remove rust and fungus formations and to prevent further collections.
Then powered the device and checked the voltages at the four protection pins out of 7 pins of Connector. The pin 6 of Thermal Detector-A was showing normal voltage like that in Pin 7. So turned my attention to the CN95 connector on the mother board. The board had array of error detecting transistors. I checked every transistor for any leak or other defects. As you can see from the following diagrams, the pin 6 was going to the base of Q907. Function of this transistor was pulling down the 3.3V volt that goes to pin 88 of the MCU when voltage was present in the pin as a result of any abnormal thermal heating of the output transistors, sensed by conducting circuit fixed on the heat zinc of each output transistor. Thus the MCU is programmed to get the alarm and to shut the set down with an error indication.
There was no voltage present and there was no reason why the set was shutting off occasionally with this error recorded. I cleaned that area as well as the pins of MCU using IPA and brushed off any residue of dirt. Checked for any change of value of SMD resistors and any leaky SMD caps.
There were none. The suspicion was on the transistor itself. So I replaced the transistor, after which, the set never had this problem again. From the following first picture, you can make out how easy it was to do trouble shooting after extending the interconnecting wires.
I tested the set for hours together and it worked fine. I also fed a video to check whether that portion was working ok. Following pictures will show you the progressive refitting of the set and the results. The extra wires were tucked underneath the MCU Board.
Thus this became a comedy story, with both hero and heroines happily living together thereafter! (LOL) Mission accomplished with a lot of satisfaction getting collected.
How happy you all are to see the result; please mention this in your comments! (LOL)
This article was prepared for you by Parasuraman Subramanian from India. He is 72 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous article on Lightning Tore Off Tracks In CCTV SMPS ERD-AD22