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Protection mode in Denon AVR-X500 solved

By on June 20, 2015
Denon repairing












I got this AVRX500 Amplifier Receiver with the complaint that it was going to Protection Mode. Red Power LED was blinking after the power on, when preliminary display round is over.   Checked and found that the complaint was accurate.   Opened the set and looked for any bulgy capacitors or any visible damages.   None!   Disconnected the power supply to Amp Board.   Then it stopped going to prot mode.  So, removed the micro control PCB from top, and then the amplifier PCB from bottom.

Denon repair




Since a free service manual was not available in the web, requested party to get it from abroad (Gulf) where he was working.   In the meantime, I connected the PCBS keeping it externally.   I replaced the control PCB with just two screws.   Then kept the Amp PCB upside down on top of the cabinet, and then interconnected the wires of AC Power in,  protect feed back cable and other data communication cable from uControl PCB.   Switched on with the same result.   Then I removed the protect feed back cable.   Set got out of protection mode, but the relays of the headphone, front L&R speakers and surround will not get on, unless the uController gets feed back.

So, I checked the protection mode connector and noticed that it had markings on the PCB, pins 4 to 7 of which were: ASO Det, DC Prot, Thermal Det A, Thermal Det B.   The first 3 pins were for driving the three relays. So, I started shorting the pins of each Det, Prot pins (4 to 7) between Amp board and the uController Board, one by one, i.e., Pin 4 of Amp Board to Pin 4 of uController, 5 5 to 5, 6 to 6, and 7 to 7.   When I shorted the DC Prot, the set switched to prot mode and led started blinking, while nothing happened with the other three.   So, confirmed it was from the DC protect.   Turned the set off, discharged the tank capacitors using a two 2.2K 10W Resistors, which were in series and covered by insulation tape, specially made for such uses, as per guidelines of Jestine Yong. See Picture below:


By that time, I got the service manual in PDF format. Took snapshot print outs of related circuits. Drew the extending circuit on the rear side of the amp circuit to save a paper:


Denon schematic



The DC protection circuit was getting feed back from front Right and Left Channel, Surround Right and Left Channels, and Centre out, I.e., all the amplifier outputs.   So, my first attempt was isolating the protect path by removing one side of jumper wires that go.   So, when I removed the jumper that goes to Front Right Channel, the set came out of protect mode.   I checked the voltage at that point.   It was showing around – 6 Volts!   So, now I knew that the culprit was inside Front Right Channel circuit.   Conducted tests as per trouble shooting chart in the service manual on the amplifier outputs and found out that these were normal.

So, started comparing the voltages between left channel, which was working and right channel, which is detected as defective.  Noticed that Transistor Q5503 (KSC1845FTA) was showing 6 V in collector whereas similar transistor in left channel was showing only 1 V.   One thing to be remembered here is that if we get positive voltage, then the problem is in the negative rail and vice versa.   Disconnected power supply, and removed the Amp PCB again (duly discharging the tank capacitors) and started probing the components one by one and noticed that Resistor 5509 (33k) was open!


Moreover, Q5502 (KSA992FTA) was seen to have corroded collector lead and it snapped when I touched it!   I replaced the transistor with 2SA992 (both are equivalent) from my stock.   Replaced the resistor.   Then, as a precaution, checked rest of the components in that portion.   Found a couple of other resistors in almost broken condition due to fungus attack and capacitors slightly out of ESR reading.   So replaced these.  While checking the components on the board, placed a tick mark on the circuit diagram simultaneously against that component, to keep a track and not to miss any!  (You can see that in the picture of AMP circuit diagram given above)  Did dry solder patch of that area.  Cleaned the PCB thoroughly.



Connected the Amp PCB back and switched on. Hurray! Set came out of protection mode and started working normally.

Denon repair protect mode


Did a test run of it for more than 3 hours. Connected various inputs and output speakers. Checked Tuner. All worked well. So, another job completed satisfactorily!

Here is the final picture:



This article was prepared for you by Parasuraman Subramanian from India. He has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company and presently working as Consultant Manager, Purchase & IT, in Irinjalakuda Cooperative Hospital.

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  1. Merlin Marquardt

    June 21, 2015 at 12:36 am

    Wow. Tough case. Good work.

  2. trev

    June 21, 2015 at 2:06 am

    excellent work

  3. Tony

    June 21, 2015 at 2:33 am

    thank you for this excerlent artical.

  4. Bernie Scott

    June 21, 2015 at 2:56 am

    Good article my friend......very good.....

  5. Gary

    June 21, 2015 at 6:58 am

    Wow I am rarely impressed by electronics repairs articles these days but this is real electronics and the guy with the beard from America cant rmemeber is name who posts here are true electronics magicians. Great in depth repair article there Parasuraman.

  6. Mohammed Kasim

    June 21, 2015 at 8:55 am

    thanks for the wonderful article. Really enjoyed the way you followed. How much it cost to get service manual?

    • Parasuraman S

      June 29, 2015 at 12:16 pm

      No idea, dear! It was provided by the customer himself from Gulf. Probably he got it free from the shop he bought the Denon Amp.

  7. Mark

    June 21, 2015 at 12:36 pm

    Hey Parasuraman,
    Well done. You can't beat schematics when trying to find difficult faults. You have an excellent grasp of electronics and how they work together.
    Keep up with the informative articles.

  8. S Ramachandran

    June 22, 2015 at 12:43 am

    Hello Mr Parasuraman ...

    i enjoyed your artical ... your fault finding approach is straight forward..

    only very few are working with schematics.. Keep posting your good work..

  9. Waleed Rishmawi

    June 22, 2015 at 4:00 pm

    great repair work. thanks for sharing

  10. Humberto

    June 23, 2015 at 12:52 am

    Hi Parasuraman Subramanian, you really worked enough to save this equipment from the dump. Congratulations and keep up.

  11. Tyrone

    June 23, 2015 at 7:27 pm

    Very good article Parasuraman,I have a Mackie amp which is also going into protect mode sometimes and this article has given me the inspiration to rapair
    this amp.

  12. Bwire Norbert

    June 24, 2015 at 6:03 pm

    Good one can I get schemati for denon avr 1804

    • Parasuraman S

      June 29, 2015 at 12:17 pm

      Pl search the web for any free manual or else try buying it from several manual online sellers.

  13. Chris

    June 26, 2015 at 3:29 am

    I really enjoyed to read your article and you don I nice description too.
    Thanks for sharing.

  14. Renuka

    August 31, 2016 at 7:23 pm

    I have almost same issue with Denon X500, can you give me suggestion where to give for repair?

  15. Felix

    October 11, 2016 at 2:24 am

    I have Denon 2105 receiver and was told CPU IC to be replaced. currently there's no stock available. Any suggestion where i can procure this part?

  16. Felix

    November 1, 2016 at 3:06 am

    Still await a response.. on my Denon AVR 2105.. or any option to rectify.. this error and still use..

  17. Jack

    January 5, 2018 at 6:52 pm

    Could you help me?
    I need a transistor number from the Q5702 position of the motherboard, such as in the pictures
    i.e. DENON AVR-X500.
    I will be very grateful.

  18. Instructor1

    April 14, 2018 at 6:50 pm

    Very impressive work, great documentation. I don't think I'd have that much patience. Thank you for the reference info.

  19. Senen

    December 3, 2019 at 8:24 pm


    I'm having troubles with this device, it goles to protect mode, red led blinking. Could someone help me?

    Thanks in advance.

  20. Ashik T A

    February 20, 2020 at 9:12 pm


    I have Denon AVR 1311 and Red light blink for sometime and I have to switch off the power for 3 times after that it will start the system.
    what could be the reason. I tried by resetting the amplifier.

    Same problem again.


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