110 lines
4.9 KiB
Markdown
110 lines
4.9 KiB
Markdown
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date = "2016-01-21"
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title = "Marantz SR5200 Repair Log"
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tags = ["ohmexpress", "repair", "audiorepair"]
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description = "A Marantz SR5200 receiver with a non-working front-right channel. Let's fix that!"
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slug = "marantz-sr5200-repair-log"
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I've been working on a Marantz SR5200 recently that came in with the front-right channel
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not outputting any sounds. Well, sounds like project!
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## Diagnostics
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First step is to see how the problem presents itself and under what circumstances. I've
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learned not to blindly rely on the symptoms a seller describes. When a seller states
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that the right speakers does not work, it really means it does not work with my current
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settings and setup.
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Again, let's first make visual inspection of the insides of the unit to make sure there
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are not already some obviously burned or damaged parts - all looked fine. Let's start
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with the head phones again to see if we get any output. Indeed, there's no sound on the
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right channel. Next, speakers, same issue.
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Now, I started playing with some buttons and testing different inputs. The issue did not
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appear when:
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1. Using the direct 7.1 input
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2. 'Source Direct' was on
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3. When using the built-in tuner
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The first and second points were a big help for me. If 'Source Direct' is on, the whole
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signal processing is bypassed, and the right channel works fine. This rules out the
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power-amp stage as the culprit and points the finger to the DSP board.
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Tracing back the schematic from what are the L+R channel outputs of the DSP board,
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I first encounter a IC725, a low noise opamp named [NJM2068M](https://octopart.com/njm2068m-new+japan+radio-419669).
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This opamp processes both analog L+R channels. Indeed, the left outputs and inputs measure
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ok, but the right channel is completely dead. On to the next IC.
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Next in line is IC720, the CS4391 24bit/192kHz DAC, which converts the digital signal
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to analog. All signal processing is digital on this device, so it makes sense for this
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IC to be by-passed in direct-mode.
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![Schematic Marantiz SR5200 / IC720](/img/marantz-sr5200-dac-schema-cs4391.png)
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Doing a quick search for the CS4391 and Marantz it becomes clear this IC is
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a common cause of trouble.
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To be sure I checked the analog input signal for the L+R channels as well. They end
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up in IC719. This IC does several things, but most importantly it has two ADCs to
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convert L+R channels to digital, and it features six DACs which are used for
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center, surround and subwoofer channels. Since the analog singal is coming in ok and
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the right surround channel is also working fine, I'm inclined to assume the
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digital processing of the right channel is also fine.
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![Schematic Marantiz SR5200 / IC719](/img/marantz-sr5200-dac-schema-cs4228.png)
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This in combination with the bad reputation the CS4391 has, I decided to replace the
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L+R channel DAC.
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## The Repair
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A replacement was quickly ordered and the TSSOP-20 IC replaced.
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Here's the original IC (IC720) on the DAC board:
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![Schematic Marantiz SR5200 / IC720-original](/img/marantz-sr5200-dac-original.jpg)
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The replacement is really easy, don't let the small size scare you. All you need is a
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soldering iron, ESD tweezers, solder wick and a flux pen.
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First removal. With a bevel point heat up one row of the IC's pins. Heat
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them up equally. Use the tweezers to left the IC off the PCB, repeat on the other
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side and the IC is gone.
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Next, you might want to use the solider wick to remove any exces solder left on the
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pads. Be careful not to damage the pads, though.
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Putting in the new IC is also not as hard as you might think.
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Apply flux liberally on one row of pads, don't be scared to touch the IC. Feed a
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little solder onto the tip of your soldering iron. With one hand use the tweezers
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to place the IC (make sure of the orientation!) and use the other to drag the
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soldering iron neatly across the pins. The applied flux will clean the
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pads and pins and make the solder flow properly.
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If you did not add too much solder, the result should be neatly soldered pins. If not,
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use your solder wick to remove exces solder, optionall re-apply some flux and
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drag again until you get it right. It might help to have a (10x) magnifying glass
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at hand to inspect your handy work.
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This is the end result:
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![Schematic Marantiz SR5200 / IC720-replacement](/img/marantz-sr5200-dac-replaced.jpg)
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As you can see the flux leaves behind quite a mess, but it's (electrically) harmless stuff,
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it just looks ugly. I really should be some flux cleaner.
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With this done, I reassembled the SR5200 receiver and voilà, nice sounding music from all
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channels as you'd expect!
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## Next steps
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![Schematic Marantiz SR5200 / IC720-replacement](/img/marantz-sr5200-front.jpg)
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During testing I noticed the volume knob not registering every step, e.g. the volume
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would not be adjusted according to how I turn the knob. This is due to the rotary encoder
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(often erroneously called poteniometer) having some dirty contacts. I've orderd some
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Kontact 60 to resolve this - and update and photos on that later.
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