Update post
This commit is contained in:
parent
8380003707
commit
bf15c8e75b
GPG Key ID:
AD739154F713697B
|
|
@ -1,9 +1,9 @@
|
||||||
+++
|
+++
|
||||||
date = "2017-09-11"
|
date = "2017-11-21"
|
||||||
title = "Denon AVR-4520 Repair"
|
title = "Repair: Denon AVR-4520"
|
||||||
tags = ["repair", "audiorepair"]
|
tags = ["repair", "audiorepair", "denon"]
|
||||||
categories = [ "Audio Repair" ]
|
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."
|
||||||
+++
|
+++
|
||||||
|
|
||||||
|
|
||||||
|
|
@ -11,49 +11,51 @@ description = "Sold from 2012-2015 as the top-of-the line AV receiver from Denon
|
||||||
## Background
|
## Background
|
||||||
|
|
||||||
Recently I came across a **Denon AVR-4520** on _Marktplaats_. I was immediately interested because it's
|
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
|
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. Reason: the AVR would _sometimes_
|
stack, including Blu-ray player and Jamo floorstanding speakers because the AVR would _sometimes_
|
||||||
go into power protection mode.
|
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
|
A red blinking light means the Denon unit is going into protection mode - most likely because of a
|
||||||
HDMI that can only be fixed with an expensive replacement of the entire HDMI board. Power protection
|
power supply failure or other fault condition that might damage the amp or connected speakers.
|
||||||
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.
|
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.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
## Diagnostic
|
## 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
|
Before hooking the devise up to mains power (I should _really_ get an isolation transfomer) I opened
|
||||||
a quick visual inspection. Although this unit is _packed_, I was able to check the amp boards and
|
it up and checked for any obvious failures: burned parts, blown fuses, etc. All seemed fine,
|
||||||
see no obvious damage.
|
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?
|
The first time powering up a unit is always exciting. Will it be able to contain the magic smoke?
|
||||||
Not this Denon. It turned on just fine. _Wait what?_ I then performed a factory reset as described
|
The unit turned on fine. I then performed a factory reset to get rid of any problematic settings.
|
||||||
in the service manual - just to erase any problematic settings.
|
|
||||||
|
|
||||||
The previouw owner claimed that the unit would _sometimes_ go into power protection mode. Ok,
|
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.
|
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
|
Time to hook up a source and a pair of headphones and see what happens. The amp played
|
||||||
with analog stereo input, as has fewer parts that could have failed already. The amp played
|
|
||||||
perfectly fine. Next I hooked up a pair of speakers and enjoyed my tunes for a bit.
|
perfectly fine. Next I hooked up a pair of speakers and enjoyed my tunes for a bit.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
I let the amp play for about an hour without issue. No power protection, just music. I hooked
|
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
|
up HDMI to my monitor and attached an UTP cable for network connectivity. Did you know this thing
|
||||||
be working fine as well as Internet radio. Why was this amp going into protection mode? And _when_?
|
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
|
That's kind of weird. The amp can run hot without issue, but starting the amp back up again whe hot
|
||||||
powering on. First test: let the amp cool down and see if it turns on. After resetting the power
|
is a no-go. But since we now got into protection mode, I could check what the amp had to say for itself.
|
||||||
protection it started up fine.
|
|
||||||
|
|
||||||
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
|
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
|
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.
|
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`
|
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
|
(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.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
This circuit monitors the amp outputs (e.g. output to the speakers) for a DC voltage. Normally, these
|
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.
|
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
|
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
|
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
|
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.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
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
|
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
|
the amp is hot. The amp did not go into protection when running and getting hot. That means
|
||||||
protection mode.
|
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
|
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
|
connects to the DC protection circuit shown above and the speaker terminals. I started unplugging
|
||||||
connectors until the amp would start up without issue. This way I quickly figured out that the `SBR` or
|
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,
|
_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.
|
I wanted to see how the DC voltage on the output behaves on a good channel vs. the bad `SBR` channel. Presumably
|
||||||
The working theory being that the `SBR` channel must be doing things the DC protection circuit does not like
|
the `SBR` channel does not stabilize quickly enough. The amp takes maybe 5-10 seconds to let the amplifier
|
||||||
_during start up_. I already confirmed the DC on the `SBR` channel was well within parameters while running
|
circuit stabilize. The `SBR` channel, when hot, seems not to be able to stabilize fast enough.
|
||||||
the amp and measuring the voltage.
|
|
||||||
|
|
||||||
This is where a 2+ channel oscilloscope comes in _very_ handy. I hooked up my scope to the `FR` and `SBR` channels
|
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.
|
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 >}}
|
{{< youtube QnaiWPzQGj0 >}}
|
||||||
|
|
||||||
It's clear that the blue `FR` DC output stabilizes much quicker than the `SBR` channel. Here's a close-up video
|
It's clear that the blue `FR` DC output stabilizes much quicker than the `SBR` channel. Also, the `SBR` channel does
|
||||||
of the scope output.
|
some weird stuff after it seems to have stabilized as well. Here's a close-up video of the scope output.
|
||||||
|
|
||||||
{{< youtube rtnBzLxHoA0 >}}
|
{{< youtube rtnBzLxHoA0 >}}
|
||||||
|
|
||||||
This is good. I now have a provable and reproducable fault condition. The output of the `SBR` channel will get
|
This is good. I now have a provable and reproducable fault condition. The `SBR` channel will output
|
||||||
a load of DC voltage during start up and seems to have trouble stabilizing when hot. Cooling down resolves the issue.
|
a DC voltage when the amp expects all channels to have stabilized. This happens only during start-up of the amp when
|
||||||
The `SBR` channel is not in use, so any heat it takes is from the heatsink.
|
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.
|
||||||
|
|
||||||
|
Now to find out which components are causing this mayhem.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
Above is the `SBR` amp board taken out of the amp. I have three things I'd like to check:
|
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?
|
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
|
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
|
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
|
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
|
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
|
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
|
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.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
With that, I've narrowed the problem down to `Q808`, a `DHCT-C3` darlington transistor.
|
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
|
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
|
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.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
Next it's a simple job to remove the old darlington transistors...
|
Next it's a simple job to remove the old darlington transistors...
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
and place the new ones.
|
and place the new ones.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
Finally re-insert the amp board into the amp with some fresh heatsink compound.
|
Finally re-insert the amp board into the amp with some fresh heatsink compound.
|
||||||
|
|
||||||
**Do not
|
**Do not
|
||||||
forget to add the insulating washers to prevent them from shorting out via the heatsink!**
|
forget to add the insulating washers to prevent them from shorting out via the heatsink!**
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
## Conclusion
|
## Conclusion
|
||||||
|
|
||||||
Replacing the DHCT-A3/C3 darlington transistor pair has resolved the power protection mode
|
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
|
issues. I've been running the amp in my living room for a few ~days~ weeks now and hae not
|
||||||
issue at all.
|
seen any problems at all.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
So, for the cost of a used entry-level AV receiver and about €15 in parts I've got
|
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
|
[hifiengine]: https://www.hifiengine.com/manual_library/denon/avr-4520.shtml
|
||||||
Loading…
Reference in New Issue
Block a user