Help repairing DT990 PRO headphones stereo image not working properly
Jun 29, 2020 at 2:36 PM Thread Starter Post #1 of 2

lemonxest

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I know this post should be in the DIY thread however I can't seem to post in there yet! Sorry If i'm posting this in the wrong place.

I bought a pair of beyerdyamic DT990 Pros second hand from eBay. The guy said nothing was wrong with them but it's partly my fault for being that gulluble he would sell them for the price and they were. Anyway I started to use them to produce and most of the time I mix in mono so I didn't notice any funny issues staright away with the stereo image or left and right channels.

So the other day though when I started mixing the stereo/ left & right channels I discovered when I pan a sound to the left it would decrease the overall volume of the headphones (left and right channels) and then when i pan to the right it seems to get louder..? Not to sure of this though as it's all based on my ears and I know they can be decieving on their own.

So I dismantled the headphones as seen in a youtube video somewhere but nobody really explains where the wires go at any point so I just need some help on the re-soldering the contacts as inside it seems like the last guy who had them attempted this and a bit of a bodge job if I'm honest.

Right headphone (working):
https://imgur.com/BmDIDL8

Left Headphone (broken):
https://imgur.com/85JL3mZ

It looks like the in the left cone it's not connected to the correct contact (white should be connected to the far right contact?) but I'm not sure
 
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Aug 4, 2020 at 1:54 AM Post #2 of 2

Arpeggione

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I am sure you have solved this problem by now. If not, here are my thoughts. Since we are talking electrical stuff, my views are just opinions, not instructions for you how to destroy amplifiers. :boom:



Both speaker elements looks identical so we assume they are. The printed +-signs that I think I see are both to the right, not mirrored. Each has 4 soldering terminals (tabs? pads?) in parallel; let’s call them L1-L4 from left to right for the Left-Ear Speaker, and R1-R4 for the Right-Ear Speaker. Orientation in space as per your photos.

Since the Right channel is working, I conclude that terminal 1 must be Ground: L1 and R1 are the ”Minus” binding posts. Must be although I can’t see any clues on the green PCB.

Left speaker: Incoming wires from amp is blue-tinted transparent (left channel +; Beyerdynamic has thereby deviated from established conventions but never mind), non-tinted transparent (common / Ground from phono plug) and red-tinted transparent (right channel +).



Time for some action. Blue-tinted transparent is in the right place (L4), so just leave that one as is. Left in the right place, to paraphrase John Cleese or something. White solid and non-tinted transparent, now on L3, shall both be moved to L1. Then L1 is Ground for both channels (they are connected at the stereo phono plug anyhow). This should make left channel working again.

Red solid and red-tinted transparent must both leave L1. (They could be soldered together and left in the air but forget that ugly solution.) Now, I can’t say if terminals L2 and L3 (and R2 and R3) are BOTH dead terminals intended just as resting places or connecting posts. Take a look at the symbols on the green little PCB (printed circuit board), pick either L2 or L3 for soldering both the red cables to the same spot. The red ones just need to be connected together again without disturbing anything else.

One problem remaining. Speakers are connected out of phase right now: relative phase error. The two cables at the Right speaker must be shifted: move solid red from R1 to R4, move solid white from R4 to R1.



Done. I think. Yeah, I really think so. But don’t blame me if ... I’m just a newbie here.

By the way, be careful with the soldering iron. Too much heat may cause the voice coil leads to disengage.
*********************


Here’s a picture, condensing all the words.

Head-Fi-936173-Beyer-990.jpg
 

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