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Denon AVR 1604 AV Surround Receiver No Power On Repair
This receiver / amplifier belongs to Sofia, a woman who is close friend of my wife. Around three months ago, Sofia asked me to see what was going on with this receiver because trying to power it on, it had no reaction at all. Below you can see its back view.
When I received the unit I opened it and performed all the basic tests. Its fuse was intact, the small linear transformer for the STBY function was OK and in general everything was in good condition but nevertheless it remained permanently in STBY no matter the number of attempts to start it.
This is a very complicated design with plenty of various and different circuits in it, both analog and digital, and without the schematic diagram there was no way to go on with it. On the other hand troubleshooting it is very difficult because it uses a modular structure with many PCBs plugged vertically on the main board.
The main board is also split in two halves which communicate by means of an interconnecting board, rendering finally the servicing process almost impossible. The first half, at the left side in reference to the heat sink, includes the power supply section and everything related to audio circuitry. The second half, at the right side of the heat sink, includes all the system control circuitry.
Structures like this one always need the use of extender cards or, alternatively, of ribbon type multiple cable extensions in order to make troubleshooting feasible or at least to facilitate it. Without these specialized tools, troubleshooting this device looks like “looking for a needle lost in a haystack”.
I dismantled the unit completely removing all the PCBs from it in order to check thoroughly the power supply section. All my findings just convinced me that this circuit was OK, but still there was no power on command on the base of the transistor controlling the activation of the main power relay. So I decided to reassemble the unit until a schematic would be available.
Below you can see a part of the power supply section of it. The main board shown at the bottom is the audio amplifier main circuit. Just before the heat sink is the power amplifier section, vertically connected to the main board and before this PCB is another peripheral audio circuit. The card you see vertically mounted on the edge of the main board (at the lower end of the power transformer or in parallel to the front cover PCB) is the “communications” card of the CPU with its peripherals. This brings the power on command from the processor located at the right side of the assembly.
And this below is a full view of this side.
This below is the right side of it.
The processor is located on the back side of the (second) main board PCB shown at the bottom, in the left side area of the bunch of the grey cables shown, exactly below the two small holes shown (hardly) in line with the last two horizontally placed resistors in this area…
After searching in the web I found both the operating and the servicing manual. First of all I confirmed that the provisional sketch I had drawn before was correct and the STBY section was functioning properly. Below you can see a photo of my (brute) sketch, drawn in an older calendar I use for keeping such notes:
Afterwards I checked the existence of protection signals informing the processor to inhibit the power on command output. Fortunately I could take relevant measurements at the terminals of the intercommunication card. This was very-very helpful. No protection was active anyway…
Next to this I inspected the structure of the CPU circuitry, especially its reset connections. Fortunately again the small electrolytic capacitor performing the “power on reset” function was located on the top side of the main board. It is the little one you see below, right above the big golden colored one which is 8200µF/6,3V cap which maintains the user set data, the preset radio stations etc which are stored in the memory of the system.
When checking the relevant function I confirmed that this cap was also OK…I was facing that familiar condition again, where everything was OK but the device was not functioning at all…
Inspecting carefully the servicing manual, I saw an important instruction which I thought that was really tailored to fit my case. You can see it below.
CAUTION IN SERVICING
- Initializing AV SURROUND RECEIVER
AV SURROUND RECEIVER initialization should be
performed when the mcom, peripheral parts of mcom,
and DSP P.W.B. are replaced.
- Switch off the unit and remove the AC cord from
The wall outlet.
- Hold the following SPEAKER A button and SPEAKER
B button, and plug the AC cord into the outlet.
- Check that the entire display is flashing with
an interval of about 1 second, and release your
fingers from the 2 buttons and the microprocessor
will be initialized
・ If step 3 does not work, start over from step 1.
・ All user settings will be lost and this factory setting
will be recovered when this initialization mode.
So make sure to memorize your setting for
restoring after the initialization
Although I didn’t replace anything relevant up to that moment, I thought to apply this re-initialization process hopping that the mcom (the processor) will function properly thereafter.
I tried this many times, following the instruction about the case of incompleteness in step 3 above, but there was no positive result. The completeness of this step was not feasible. No display at all and when releasing my fingers from the two speaker buttons there was only flashing of the STBY led. In every new attempt, the processor was for some reason stuck somewhere in its algorithm, always at the same point.
I searched to find this chip here in the local market but I didn’t find it anywhere…I kept on searching in the web and I spotted a seller of original Denon spare parts in the U.K. Now I had my hands tied because I couldn’t order it, as things are very complicated here for the time being due to capital controls…So I informed Sofia about my findings and my conclusion, giving her the necessary data of this chip, after copying them from the servicing manual, and asking her if she had a means to obtain this IC. If you are interested in this info, here are the relevant data: IC 201, Part Number: 963 0121 305, CXP 740096 -178Q, for models AVR-1604/684/AVC-1580.
Fortunately one of Sofia’s sons was working in Portugal. So she sent him all the relevant info for ordering it and sending it here thereafter. This took a long time, but anyway I had the IC in my hands a week before. Then I continued the repair process.
I dismantled the unit again and removed the processor. You can see below its location on the main board, after the necessary cleaning of the area.
And the dead one, below
Thereafter I reassembled the unit, being anxious to see the result. You can see it in the pictures below:
The set was functioning perfectly and I extinguished my anxiety by enjoying the high quality of the reproduced music…
After confirming that everything was in order, I informed Sofia that her amplifier was alive again and she could arrange to pick it up. She was very happy with the good news…
One more repair was successfully completed.
This article was prepared for you by Paris Azis from Athens-Greece. He is 59 years old and has more than 30 years’ experience in electronics repairs, both in consumer and industrial electronics. He started as a hobbyist at the age of 12 years and ended his professional carrier as a senior electronics technician. He has been a specialist in the entire range of consumer electronics repairs (: valve radio and BW TV receivers, transistorized color CRT TV, audio amps, reel and cassette tape recorders, telephone answering and telefax devices, electric irons, MW cooking devices e.t.c) working in his early stages at the official service departments of National-Panasonic first and JVC afterwards, at their premises in Athens.
Then he joined the telecoms industry, working for 20 years as field supporting technician in the sector of DMRs (: Digital Microwave Radio transmission stations), ending his carrier with this subject. Now he is a hobbyist again!
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Note: Please check his previous repair article in the below link: