Add marantz pm80 repair log

content/posts/2016-10-09-marantz-pm80-mk2-repair-log.md

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