Audio Technica At8024 issue

Hi all
I bought on ebay for less than 80€ +shipping a stereo microphone Audio Technica AT8024. The german seller wrote it was very worn, instead the one I received is like new(!), but it makes noise in stereo mode and audio is always mono, also in stereo mode! It could be a switch issue, but it is steady, because I never hear a difference between the two channels. For the cheap price, I'd like to repair and keep it.

The first problem is how to open the back! I tried with adjustable pliers and an old inner tube so as not to scratch it, but I was unable to open it. I also tried heating with the 858D hot air station set to 360°C, but with no success... :(

Can anyone help me?



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Oh! I inserted the back of the microphone INSIDE the inner tube (it was exactly the same diameter!) and it has been simple to unscrew it by the adjustable pliers.
The first problem is solved!

Does anyone have the schematic diagram? I've searched, but I haven't found it...

Switches seem to be ok... There are two double switches coupled: a section is only for power; two sections are for audio switching and the fourth is not used.
Side microphones are working, but output is mono... :(
After working two days for a total of about 8 hours, I solved the problem: the High Pass switch was a single switch, instead of a double switch! It has 6 pins, but they are 2 by 2 in parallel, then the two channels were mixed together! >:( Audio Technica mounted a wrong switch... I replaced it with another one previously salvaged, very similar to that one, and now it works perfectly! :)
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You would have thought that something that major would have been caught by quality control. At least you've got a good working mic for a bargain plus some detective work. There's nothing wrong with that.
I thought the bargain was because the seller said that it was very worn... Instead, I think he sells all defective or incomplete stuff!
I have written to the seller and he offered me a 30€ discount for my next purchase! :) (but 14.90€ are for shipping...)