Sennheiser HDR120 - missing transmitter / alternative OR replacement?

Sennheiser Wireless Headphone HDR 120 Instruction Manual
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read

Probably a defective item, Try for a return.

wiring

If you twist the earpiece,one of them has two NIMH AAA batteries ,worth checking out if these are gone ,which is what happened to me.I was about to bin my rs130's and just stuck two new rechargeables and the earphones are working again!!!!!

As for $20 dollars from sennheiser for replacements!?!?!?
You should pick up two NIMH batteries for a couple of bucks on ebay or amazon.DO NOT USE ORDINARY BATTERIES!!!!!

The volume of the sound source (Mac) must be sufficient, otherwise the transmitter automatically turns off. Turn up the volume on the Mac, and turn down the volume on the headphones. There is no way to disable the Automatic On/Off function of the transmitter.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Broken audio cable entering the transmitter or audio jack plug.

Power supply plug loose / faulty power supply.

Twist the pad counterclockwise on the left earpice. You'll find the batteries underneath.

You can buy the HDR 120 model which is basically the headphones lone
These will work with the base in conjunction with the set you have now.. or as a replacement
You can also buy replaceable ear cups for less than 20 dollars (check the Sennheiser website)
Finally you may want to replace the rechargeable batteries in the headphones you have
Just make sure you replace them with the exact type.. I believe those are NiMh AAA
Pop them out and go to any Battery Plus or Radio Shack.. a new set probably run you less than 7 bucks
My point.. for less than 30 dollars you can have your old headphones working and looking like new ones
Give the new batteries an overnight charge before using them

Good luck

A replacement battery can be purchased from Sennheiser for $20.00.

Battery is: BA 151

Sennheiser Link:
http://www.sennheiserusa.com/newsite/productdetail.asp?transid=004146