Add denon repair log post

content/posts/2016-01-07-denon-pma560-repair-log.md

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