Add denon repair log post
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content/posts/2016-01-07-denon-pma560-repair-log.md
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content/posts/2016-01-07-denon-pma560-repair-log.md
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date = "2016-01-07"
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title = "Denon PMA-560 Repair Log"
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tags = ["ohmexpress", "repair", "audiorepair"]
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description = "Log of diagnosing and repairing a Denon PMA560 Stereo Receiver."
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slug = "denon-pma-560-repair-log"
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I recently found a Denon PMA-560 Stereo Receiver for sale with the remark that the
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left channel had stopped working. For a small fee the seller shipped the unit to me
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and this is the log of diagnosing and fixing the issue.
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## The Denon PMA-560
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![Denon PMA-560 Front][denon-560-front]
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First, something about the Denon PMA-560. It's a Stereo Receiver from 1991 and is
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an analog design. I can really appreciate this design, using no digital IC's or MCU's.
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As always I was able to find a trove of information on this receiver at
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[hifiengine.com](http://www.hifiengine.com/manual_library/denon/pma-560.shtml), including
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a scan of (a German version of) the service manual.
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## The complaint
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I bought this receiver on Marktplaats, a Dutch alternative for Craigslist, with the remark
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that the left channel had stopped working. This could be due to a lot of things, but it
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will probably be fixable.
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## Diagnosing the problem
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The first step with any repair job I do, before connecting it to mains and powering it on,
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is to open up the device and check for any obvious signs of malfunction: blown fuses,
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leaking or buldging capacitors, fried resistors or other burned looking things,
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disconnected wires, etc.
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A first inspection showed that everything looked the way it should. There was little bit
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of dust, which was quickly taken care of.
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Time to turn it on!
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To be safe, I always start with, if possible, disabling the speaker outputs. The PMA-560
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has a nice rotatary selector on the front turn the A and B speaker connectors on or off
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- it turned them all off and connected a pair of headphones.
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Next, I hooked up my CD player to the CD input, turned the volume all the way down and
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powered it on. Nothing exploded. Yay!
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Slowly increasing the volume revealed that both the left and right channel on the
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headphones were working just fine. I also tested the different inputs (omitting the
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phono input for now) and everything worked beautifully. Also the balance,
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bass, treble and loudness buttons worked as expected.
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Next up: speakers.
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First, I connected two 8Ω speakers to the A-channel, and as expect no sound on the
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left speaker. Connecting the speakers to the B-channel, however, had the same effect
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as the headphones: great sound on both left and right channels.
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These simple tests told me several things:
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* The power-amp section is working fine for both the left and right channel.
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* The inputs work correctly.
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* The adjustment section works ok.
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* Headphones and B-channel work fine.
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* Only the left speaker for A-channel is not working.
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## Finding the root problem
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The service manual (you can find it on hifiengine.com) contains the full schematic and
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it was rather easy to trace the single point of failure for this particular set of
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symptoms.
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![Denon PMA-560 Schematic][denon-schematic]
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In pink I've indicated the wire connection to the headphone PCB, where the headphones
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are connected. In blue are the three relays that enable/disable each channel or
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headphones.
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If you follow the lines you see that the left channel goes straight to the A, B and
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headphone outputs. The same goes for the right channel. The only point of failure
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between the common left channel output and the A-channel left output is relay, RL602.
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It's not surprising that after about 25 years of turning off and on again, the relay
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for channel A encountered a (probable) mechanical failure. I tried the speaker selector
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and the RL602 makes a distinct, heavier sound than RL601 for B-channel.
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## The fix
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![Denon PMA-560 Faulty Relay][denon-relays]
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The fix is still pending. The relays are clearly marked and a Denon part number is
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specified in the service manual. Finding a replacement part was straightforward and
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a new relay in currently in the mail. In a few days I'll replace the relay, which
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will most likely make A-channel fully functional again.
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What I liked most about this repair is that is was very easy to diagnose. I didn't
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even touch my multimeter or scope. Stay tuned for an update when the relay has been
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replaced.
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[denon-560-front]: /img/denon_pma-560_front_panel.jpg "Image courtesy of hifiengine.com"
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[denon-schematic]: /img/denon-pma-560-schematic.png "Part of the PMA-560 schematic, taken from the Service Manual."
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[denon-relays]: /img/denon-pma-560-relays.jpg "Detail of RL601 and RL602"
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