Add marantz pm80 repair log
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content/posts/2016-10-09-marantz-pm80-mk2-repair-log.md
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content/posts/2016-10-09-marantz-pm80-mk2-repair-log.md
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date = "2016-10-09"
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title = "Marantz PM80 Mk2 Repair Log"
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tags = ["repair", "audiorepair"]
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description = "The venerable Marantz PM80 Mk2. This unit was completely dead, but I was able to bring it back to life!"
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slug = "marantz-pm80-mk2-repair-log"
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The Marantz PM80 Mk2. The Hi-Fi connaisseur knows what I'm talking about.
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The amp sounds amazing when in Class AB mode (100Wpc), but it can also be switched
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to Class A mode (25Wpc) for _intesive listening sessions_ with even lower distortion. \m/
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This unit was defective: it did not work at all. The power light would come on, but
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nothing else.
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Note that this is a MkII model. The MkI and SE models have a STK amplifier IC that tends
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to break often, but no replacment is readily available. The MkII does not have this
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STK module, so there's that.
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## Diagnostics
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![Marantz PM80 Mk2 Opened up](/img/marantz-pm80-mk2-opened.jpg)
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First a visual inspection. There's a huge power transformer and two _very_ large
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capacitors. The power FETs are mounted on two separate heatsinks.
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A quick look around reveals nothing out of the ordinary. No burnt parts, not buldging
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capacitors, no blown fuses. Time to turn the volume to 0 and turn it on.
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After powering on the amp, nothing happens. The power LED comes on, but that's it.
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Normally I'd expect to hear the speaker relays click - but they didn't. If one didn't
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click, that might be a mechanical failure of the relay. Both not clicking means there's
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something wrong.
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Time to grab the multimeter and do some measurements. First, the mains input and
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transformer board. This is the `/22` model. All inputs and outputs measure good voltages.
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![Marantz PM80 Mk2 Power Schematic](/img/marantz-pm80_mk2_transformer.png)
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Because the speaker relays are not clicking on, I measured the outputs (on the PCB) for
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DC voltage. Ideally, speaker outputs should measure 0V, but nothing being perfect, a
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few mV of DC is okay. Anything above 0.1V should be considered a fault, however. I
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measured 0.33VDC - not good. The protection circuitry detected the DC voltage and kept
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the relays off to protect any attached speakers.
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So, why is there a DC voltage on the outputs? This could be for a number of reasons
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ranging from failed components, bad solder connections to a failed power supply.
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![Marantz PM80 Mk2 Amp Board](/img/marantz-pm80_mk2-amp-board.png)
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I worked my way back from the speaker terminals through the schematic, measuring
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the voltages mentioned. I quickly discovered that the ±57V (from J705) were too
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low: 1.1V and -0.14V. J704 comes directly from the transformer board with ±60V,
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but J705 comes from a separate power regulator board.
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![Marantz PM80 Mk2 Regulator Board](/img/marantz-pm80_mk2-regulator-board.png)
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Because the input AC voltages (J851 1-3) looked all right, but the DC voltages (J855)
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were way too low, the problem should lie between those points.
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Capacitors C857 and C858 appeared in good working condition (no damage, leaking,
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buldging). All diodes (D865-D872) measured at a nice 0.6Vf.
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Resistors R859 and R860 measured in at 2.3MΩ and 163kΩ respectively.
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Wait a minute. Those should measure at 1Ω. Whoops.
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![Marantz PM80 Mk2 Regulator PCB](/img/marantz-pm80-mk2-regulator-pcb.jpg)
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The resistors don't seem to have failed catastrophicaly, going out in a blaze
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of magic smoke. Instead, they seem to have failed from a longer period of
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intensive use.
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## Repair
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1Ω 1/4W resistors are something I have plenty of. Replacing them was very
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easy as the regulator board is snapped in by two plastic holder pins. Removing
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and replacing it was easy.
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With the resistors replaced, the output is back to ±57V and the speaker relays
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click into actions when powering on the amp.
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Moment of truth: connect testing speakers and an audio source. Slowly turning
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up the volume. It's back in action!
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Although I like the Pioneer VSX-921-K I'm currently using (especially the
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AirPlay feature), it pales in comparison to the sound quality of this
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monster. It's a great match for my Sennheiser HD650's as well.
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So, this is a keeper :-) I'll build some DAC/AirPlay device myself, but the
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PM80 stays. ♥️
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![Marantz PM80 Mk2 in action](/img/marantz-pm80-mk2-in-action.jpg)
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## Notes
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The service manuals for the Marantz PM80 are available for free at [hifiengine](http://www.hifiengine.com/manual_library/marantz/pm-80.shtml).
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