From bf15c8e75b741bac095ca6d0efa15ec97ed767d2 Mon Sep 17 00:00:00 2001 From: Ariejan de Vroom Date: Tue, 21 Nov 2017 15:42:47 +0100 Subject: [PATCH] Update post --- content/electronics/repair-denon-avr-4520.md | 138 ++++++++++--------- 1 file changed, 74 insertions(+), 64 deletions(-) diff --git a/content/electronics/repair-denon-avr-4520.md b/content/electronics/repair-denon-avr-4520.md index 390b340..a9a67f4 100644 --- a/content/electronics/repair-denon-avr-4520.md +++ b/content/electronics/repair-denon-avr-4520.md @@ -1,9 +1,9 @@ +++ -date = "2017-09-11" -title = "Denon AVR-4520 Repair" -tags = ["repair", "audiorepair"] +date = "2017-11-21" +title = "Repair: Denon AVR-4520" +tags = ["repair", "audiorepair", "denon"] categories = [ "Audio Repair" ] -description = "Sold from 2012-2015 as the top-of-the line AV receiver from Denon, I got my hands on a unit with power protection issues. Here's the repair log the Denon AVR-4520." +description = "This unit sold from 2012-2015 as the top-of-the line AV Network Receiver from Denon. I got my hands on a unit with power protection issues. Here's the repair log the Denon AVR-4520." +++ ![Denon AVR-4520 - Front view](/img/denon-avr4520-frontview.jpg) @@ -11,49 +11,51 @@ description = "Sold from 2012-2015 as the top-of-the line AV receiver from Denon ## Background Recently I came across a **Denon AVR-4520** on _Marktplaats_. I was immediately interested because it's -a Denon, an undamaged high-end model, and sold with a defect. The seller was dumping his entire AV -stack, including Blu-ray player and Jamo floorstanding speakers. Reason: the AVR would _sometimes_ -go into power protection mode. +a Denon, a high-end model, undamaged, and sold with a defect. The seller was dumping his entire AV +stack, including Blu-ray player and Jamo floorstanding speakers because the AVR would _sometimes_ +go into power protection mode, altough it was described as _it doens't work, only a red light is blinking_. +He also mentioned that the problem was not consistent. Sometimes the unit would start up and work fine +for hours, other times the unit would start up to a blinking light. -I tend to stay away from AVRs that have no audio or video. 9 out of 10 times there's an issue with -HDMI that can only be fixed with an expensive replacement of the entire HDMI board. Power protection -faults can be caused by many different issues, but I'm mostly can be fixed by replacing a few damanged -components. After some haggling I bought the unit and received it a few days later. +A red blinking light means the Denon unit is going into protection mode - most likely because of a +power supply failure or other fault condition that might damage the amp or connected speakers. + +Power protection faults can be caused by many different things, but can often be fixed by replacing a +few damanged components. After some haggling I bought the unit and got it in the mail a few days later. ![Denon AVR-4520 - Back view](/img/denon-avr4520-backview.jpg) ## Diagnostic -With the **Denon AVR-4520** on my bench I was ready to start diagnostics. +With the **Denon AVR-4520** on my bench I was ready to start diagnosing the problem. -Before hooking up any new device to mains power and powering it up I like to lift the cover and do -a quick visual inspection. Although this unit is _packed_, I was able to check the amp boards and -see no obvious damage. +Before hooking the devise up to mains power (I should _really_ get an isolation transfomer) I opened +it up and checked for any obvious failures: burned parts, blown fuses, etc. All seemed fine, +which was consistent with the what seller told me. -The first time powering up a unit is exciting. Will it blow up? Will it release its magic smoke? -Not this Denon. It turned on just fine. _Wait what?_ I then performed a factory reset as described -in the service manual - just to erase any problematic settings. +The first time powering up a unit is always exciting. Will it be able to contain the magic smoke? +The unit turned on fine. I then performed a factory reset to get rid of any problematic settings. The previouw owner claimed that the unit would _sometimes_ go into power protection mode. Ok, let's see if I can reproduce that. I turned the amp off an on about 30 times. No problems. -Time to hook up a source and a pair of headphones and see what happens. I prefer starting out -with analog stereo input, as has fewer parts that could have failed already. The amp played +Time to hook up a source and a pair of headphones and see what happens. The amp played perfectly fine. Next I hooked up a pair of speakers and enjoyed my tunes for a bit. ![Testing the Denon AVR-4520](/img/denon-avr4520-testing-01.jpg) I let the amp play for about an hour without issue. No power protection, just music. I hooked -up HDMI to my monitor and attached an UTP cable for network connectivity. HDMI Out seemed to -be working fine as well as Internet radio. Why was this amp going into protection mode? And _when_? +up HDMI to my monitor and attached an UTP cable for network connectivity. Did you know this thing +has a built-in network switch? HDMI worked fine as well as Internet radio. Why was this amp going +into protection mode? And _when_? -Then I turned it off and on again: power protection mode! +After listening to some music from about two hours, I turned the amp off and on again: _power protection mode_! +Finally! -Aha! My assumption was that the amp does not fail when getting hot, but does fail when hot and -powering on. First test: let the amp cool down and see if it turns on. After resetting the power -protection it started up fine. +That's kind of weird. The amp can run hot without issue, but starting the amp back up again whe hot +is a no-go. But since we now got into protection mode, I could check what the amp had to say for itself. -Next I checked the error messages to see what _kind_ of power protection was triggered. The service +I checked the error messages to see what _kind_ of power protection was triggered. The service manual tells me to power on the amp with `ZONE/REC SELECT` and `STATUS` buttons pressed, then select `2. PROTECTION`. This restarts the amp in diagnostics mode. Pressing the `STATUS` button allows you to browse view the last type of power protection triggered. @@ -62,39 +64,41 @@ you to browse view the last type of power protection triggered. So, **DC Power Protection**. The service manual provides the following bit of schematic. The `DCDET` (for DC Detection) net goes to the CPU and should be _active low_, meaning that measuring ~0V triggers -protection mode. +protection mode and any voltage (probably 3.3V or higher) means that everything is dandy. ![DC Power protection circuit](/img/denon-avr4520-dc-protect-circuit.png) This circuit monitors the amp outputs (e.g. output to the speakers) for a DC voltage. Normally, these -outputs are _very_ close to 0VDC and have only an AC voltage. Having any significant DC output can and +outputs are _very_ close to 0VDC and have only an AC voltage. Having any significant DC output will damage your speakers, so it's a good thing the amp shuts itself down when there's a problem. To figure out which channel(s) are outputting DC I first measured each channel with my multimeter. To do this, turn on the amp, select an input that has no signal coming in and turn the volume all the way down. You cannot measure the DC directly on the speaker terminals on the back, because they may not be -enabled (e.g. if running in `STEREO` mode, only FL+FR are enabled). +enabled. E.g. if your running in `STEREO` mode, only FL+FR are enabled with relays. The rest is simply +disconnected. ![Measuring DC on speaker outputs](/img/denon-avr4520-dc-on-output.jpg) -All channels were withing 3mV of `GND`, so no issues there _when running the amp_. +All channels were withing 3mV of `GND`, so no issues there _when the amp is running_. -Then I remembered that the problem with DC protection only occurs when powering up the amp _and_ when -the amp is hot. To do this, I let the amp run for about 30 minutes, cycled the power and it went into -protection mode. +Remembered that the problem with DC protection only occurs when powering up the amp _and_ when +the amp is hot. The amp did not go into protection when running and getting hot. That means +that the fault condition that triggers the DC protection _only_ occurs when booting up the +amplifier. Each channel has its own little amp board with an easily accessible connector for the output. This output -connects to the DC protection circuit shown above and the speaker temrinals. So I started unplugging -connectors until the amp would start up without issue. This way I quickly figured out that the `SBR` or +connects to the DC protection circuit shown above and the speaker terminals. I started unplugging +connectors one by one until the amp would start up without issue. This way I quickly figured out that the `SBR` or _Surround Back Right_ channel was the one causing the DC Protection mode. With just that board disconnected, -the problem does not occur. +the problem did not occur. -Knowing the issue lies in one specific channel helps a lot (especially since this is an 11.2 channel amp). +Knowing the issue lies in one specific channel helps a lot, especially since this is an device has 9 +discrete channels. -Next I wanted to see how the DC voltage on the output behaves on a good channel vs. the bad `SBR` channel. -The working theory being that the `SBR` channel must be doing things the DC protection circuit does not like -_during start up_. I already confirmed the DC on the `SBR` channel was well within parameters while running -the amp and measuring the voltage. +I wanted to see how the DC voltage on the output behaves on a good channel vs. the bad `SBR` channel. Presumably +the `SBR` channel does not stabilize quickly enough. The amp takes maybe 5-10 seconds to let the amplifier +circuit stabilize. The `SBR` channel, when hot, seems not to be able to stabilize fast enough. This is where a 2+ channel oscilloscope comes in _very_ handy. I hooked up my scope to the `FR` and `SBR` channels to see what the DC voltage on each channel does during start up. @@ -103,18 +107,21 @@ Blue is the `FR` channel, which works correctly, yellow is the bad `SBR` channel {{< youtube QnaiWPzQGj0 >}} -It's clear that the blue `FR` DC output stabilizes much quicker than the `SBR` channel. Here's a close-up video -of the scope output. +It's clear that the blue `FR` DC output stabilizes much quicker than the `SBR` channel. Also, the `SBR` channel does +some weird stuff after it seems to have stabilized as well. Here's a close-up video of the scope output. {{< youtube rtnBzLxHoA0 >}} -This is good. I now have a provable and reproducable fault condition. The output of the `SBR` channel will get -a load of DC voltage during start up and seems to have trouble stabilizing when hot. Cooling down resolves the issue. -The `SBR` channel is not in use, so any heat it takes is from the heatsink. +This is good. I now have a provable and reproducable fault condition. The `SBR` channel will output +a DC voltage when the amp expects all channels to have stabilized. This happens only during start-up of the amp when +hot. Letting the amp cool down resolves the issue. -Now as to what is causing this and how to fix it! +Eventhough the `SBR` channel is not in use (I was running in stereo mode), the problem occurs. The heatsink +will warm up the attached darlington transistors either way. -![](/img/denon-avr4520-sbr-amp-board.jpg) +Now to find out which components are causing this mayhem. + +![The Surround Back Right amplifier board](/img/denon-avr4520-sbr-amp-board.jpg) Above is the `SBR` amp board taken out of the amp. I have three things I'd like to check: @@ -123,11 +130,11 @@ Above is the `SBR` amp board taken out of the amp. I have three things I'd like 3. Power darlington transistors: any obvious shorts? How do they react to heat? I always measure resistors in circuit first. This works fine most of the time and when I get a weird -read out I can desolder them when I'm working on the capacitors. All of them seem fine. +read out I can desolder them when I'm working on the capacitors. All of them seem fine and within spec. -Next I desolder one (or two) legs of each electrolytic capacitor. I always mark their orientation in +Next I desolder one (or if need be two) legs of each electrolytic capacitor. I always mark their orientation in relation to the board before taking them off. Some PCBs have polarity indicators, some do not. All -electrolytics measure within their specifications for capacitance and ESR. So no issues there. +electrolytics measure within their specifications for capacitance and expected ESR. So no issues there. That leaves the darlington transistor pair. My gues is that they start to misbehave when hot. Keep in mind that the `SBR` channel is not used in my stereo configuration, so they do not produce any heat @@ -139,9 +146,9 @@ darlingtons is simple: 3. Freeze spray each of the darlingtons to see if it resolves the problem Freezing the `DHCT-A3` has no effect on power protection. Freezing the `DHCT-C3` however makes -the problem go away. +the problem go away immedately. -![](/img/denon-avr4520-darlingtons.jpg) +![Your friendly neighbourhood Darlington Transistor Pair](/img/denon-avr4520-darlingtons.jpg) With that, I've narrowed the problem down to `Q808`, a `DHCT-C3` darlington transistor. @@ -149,36 +156,39 @@ With that, I've narrowed the problem down to `Q808`, a `DHCT-C3` darlington tran As with almost every project, diagnosing the issue is much more time consuming than the actual repair. I ordered a _new old stock_ pair of transistors, this is a set of complimentary -`-A3` and `-C3` transitors including two insulating washers. +`-A3` and `-C3` transitors including two insulating washers. These are +genuine Denon parts. -![](/img/denon-avr2520-new-transistors.jpg) +![New darlington transistors](/img/denon-avr2520-new-transistors.jpg) Next it's a simple job to remove the old darlington transistors... -![](/img/denon-avr4520-new-and-old.jpg) +![Transistor Transplant](/img/denon-avr4520-new-and-old.jpg) and place the new ones. -![](/img/denon-avr4520-new-transistors-soldered.jpg) +![Shiny new Darlington transistors](/img/denon-avr4520-new-transistors-soldered.jpg) Finally re-insert the amp board into the amp with some fresh heatsink compound. **Do not forget to add the insulating washers to prevent them from shorting out via the heatsink!** -![](/img/denon-avr4520-final-solution.jpg) +![SBR Mounted back onto the heatsink, ready for action](/img/denon-avr4520-final-solution.jpg) ## Conclusion Replacing the DHCT-A3/C3 darlington transistor pair has resolved the power protection mode -issues. I've been running the amp in my living room for a few days now and not seen any -issue at all. +issues. I've been running the amp in my living room for a few ~days~ weeks now and hae not +seen any problems at all. -![](/img/denon-avr4520-final-setup.jpg) +![Current Denon AVR-4520 Setup with my Technics SL-3310 turn table](/img/denon-avr4520-final-setup.jpg) So, for the cost of a used entry-level AV receiver and about €15 in parts I've got -an almost brand new Denon AVR-4520 top-of-the-line AV Receiver. :-) +an almost brand new Denon AVR-4520 top-of-the-line AV Receiver. :-) _I'm not reselling this +one any time soon_. -_For those interested, I'm using the `SBR/SBL` channels to bi-amp my speakers._ +_For those interested, I'm currently using the `SBR/SBL` channels to bi-amp my speakers. No, I +don't hear any difference, but I've got 6 unused channels in my setup, so why not use them?_ [hifiengine]: https://www.hifiengine.com/manual_library/denon/avr-4520.shtml \ No newline at end of file