MTR5B is not working with batteries

[W4RAM]

Good morning,
Asking for assistant with the following issue:
My MTR5B is not working with batteries. I tried with one 9v battery, also with a battery case x 6AA using Ni-MH 1.2v 2850 mAh, and also a LiPo 7.4v 5200mAh with the same result.

If I use 12-13.8v power supply radio works fine. If the damage is related because I feed the radio with a 13.8v power source, how can I fix it?
Thank you for your assistant,

    Al
    W4RAM

[gil]

Hello, I saw on another forum that you solved the issue?

Gil.