169 lines
7.1 KiB
Markdown
169 lines
7.1 KiB
Markdown
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date = "2016-01-07"
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title = "Repair: Denon PMA-560"
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tags = ["denon", "repair", "audiorepair"]
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categories = [ "Audio Repair" ]
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summary = "Log of diagnosing and repairing a Denon PMA560 Stereo integrated amplifier."
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aliases = [
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"/2016/01/07/denon-pma-560-repair-log/",
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"/2016/01/12/denon-pma-560-repair-log-update/"
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]
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[image]
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+++
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I recently found a Denon PMA-560 Stereo integrated amplifier 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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![](/img/denon_pma-560_front_panel.jpg)
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First, something about the Denon PMA-560. It's a Stereo Integrated Amplifier 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 unit 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 Denon 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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# Update 12 Januari 2012
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Last week I diagnosed a Denon PMA-560 Integrated Stereo Amplifier. The device worked fine
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since its production in 1990, but had lost output on the left channel. My diagnosis, as
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you can [read in the previous repair log][repair-log] was a defect in the A-Channel
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relay.
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## There and back again
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It sounds straightforward: just replace the A-channel relay. And it is. But does require
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a bit of work and careful deconstruction of the unit.
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![Original Relays of the Denon PMA-560](/img/denon-pma-560-situation.jpg)
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Those are the original relays. On the left you can see some metal pins connected to the
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PCB, those are the speaker terminals that you can see protrude out the back. This PCB is,
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on one side, firmly pressed against the back panel of the case and other the other side
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wedged in by the big transformer. The PCB itself is held in place by three white plastic
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pins. Can you spot them?
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To remove the PCB, as I need to do some soldering work on the bottom side, I'd need to
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remove the back panel, which amounts to 15 screws. After that, the PCB comes loose and
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the soldering iron can be heated up.
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## Replacement
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The first problem is that the schematic in the service manual sports two RL602 devices.
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I've marked the three relays in green. RL601 and RL602 are for the A and B speaker channels.
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The second relay also RL602 in the schematic is for the headphones. Luckily this relay
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has different size and shape and is correctly marked as RL603 on the PCB silkscreen.
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![Error in the schematic](/img/denon-pma-560-schematic-2.png)
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The relay has six pins, which are soldered to the PCB. Using my soldering iron and
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desoldering pump I first removed most of the solder and then wiggled the relay free
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while quickly heating up each pin.
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![Relay removed](/img/denon-pma-560-removed-relay.jpg)
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Next up, insert new relays and solder it to the PCB.
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![Relay replaced](/img/denon-pma-560-replaced-relay.jpg)
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Here is the new relay in place. As you can see it's the same make and model as
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it's malfunctioning predecessor.
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Let's get the PCB back in, re-attach the back plate and hook the unit up to some speakers
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and input.
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## Moment of truth
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Yes. It worked. Turn on some music, select the correct input, select A-channel speaker output
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and slowly turn up the volume to the voice of Adele.
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After this I did a double-check that I reconnected all wires and put the device back
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together (including the 15 screws on the back, not counting the three for the top cover).
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Here is the restored Denon PMA-560 Integrated Stereo Amplifier, fully tested and working.
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![Denon PMA-560](/img/denon-pma-560-project-completed.jpg)
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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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