[AudioCats]

I bought a pair of "as-is for repair/parts" he560 off ebay to play with. It is the "adorama exclusive" V4 version and seller was adorama so I suppose it was a customer-returned unit.

Phones were in pretty good condition, probably used very little before being returned.

The symptom was "audio only come out of right side". measured at the phone jack (inside the ear cup, after removing the grill),
-- right driver DC resistance is 40 ohms,
-- left driver measured open.

left (open) driver inspection:
by measuring the continuity along the silver traces on the diaphragm, I could more or less pin-point the location where the discontinuity happen, but did not see the crack in the coating (under ~20x magnification). so it was a very fine crack. Then I noticed the diaphragm is attached to the magnet bar around that area, instead of having an air gap between the diaphragm and the magnet.

red-circled areas = diaphragm glued to magnet
(the blue arrow points to the location of coating crack but that is on the other side of the magnet bar, not visible in the photo below)

white-circled area = good air gap

I guess what might have happened was:
1) some kind of glue contamination got under the magnet bar and glued the diaphragm to the magnet bar.
2) because the rest of the diaphragm could still vibrate and make sound, the driver passed the "sound check" ( ? but it probably would not sound the same as a normal driver)
3) the "glued" area becomes a stress point. After some use, the diaphragm film stretched at that location but the conductive coating couldn't stretch to the same degree ==> micro-crack formed in the coating ==> open circuit.

kind of a strange failure mode. I supposed by the time the diaphragm assembly was attached to the magnet plate assembly, the epoxy holding the magnet bars should have hardened fully (otherwise the magnet bars will move and slam into each other). Then when did this (wet glue) contamination occur?

The good news is, this problem is easy to detect via visual inspection, just remove the grill and take a look. (But visual inspections should have been done (multiple times) during manufacturing process... instead of being performed by the end user )

 

[dunring]

There's a couple of videos showing repair on them, but the only place I've seen that offers to repair planars is Vesper Audio. They also have a QC problem I've run into on the HE4xx twice of not putting enough threadlocker on the negative ground screw and it vibrates loose. If you see them with one side working on ebay, it's usually that screw or a failed cable and they didn't try reversing the plugs to test. Liquidators never check that kind of thing since they have a warehouse to get rid of. I check for used items every day and Hifiman has more failures than any other headphones in the "parts or not working" category. In China, quality control isn't the same as it is here. I'm sure it can happen, but I've had tons of stuff from Schiit, Grado, and JDS Labs and never had anything fail on me due to a defect in it. Look on eBay, and you'll see 5-6 Drop THX 789 amps in protection mode for parts at any given time by comparison.

 

[AudioCats]

I might get another pair of "one side working" he560, to put together a working pair.

but maybe not.......

I took apart the failed driver to investigate further. I gently wiggled the diaphragm ring but the spot that got "glued" to the magnet was stuck on good, I ended up tearing the diaphragm (well it was a dead driver anyway so not much was lost there), with a small piece of film material staying on the magnet bar.

However...... I was then able to "peel" this small piece off the magnet without difficulty. And the magnet surface did not feel sticky. So what was holding it before? This is on the magnet/grill side of the diaphragm, maybe something (vapor or liquid) got in there and got the diaphragm "glued"?

This might not be an manufacturing issue after all. The drivers could have been ok from the factory but something got into the cups during use. This might mean the drivers checked out ok now might "develop" similar problem later on. (especially if with the the grills removed, anything can easily get to the magnet and diaphragm).