Quest to repair TM600

[Ism]

I have a Whites TM600 (very similar to TM800 via schematics I have). Never having used the detector, I am not sure it is functioning properly.
Somewhere along the line, an owner left batteries in till they leaked acid inside.

So now I have it and here's what it does;

Battery test emits loud tone from the speaker (meter works). Based on my limited interpretation of the schematic, I don't think the battery check should emit a tone.
Can somebody tell me what is normal?

Other controls seem to function and it appears to detect properly. But audio is very loud.

[Ism]

Aaah, after doing some testing and looking at the schematic more, it seems that the audio circuit IS powered in battery test mode.
What an annoying feature. The manual is vague in explaining what to expect during operation. No youtube videos to demonstrate either model (tm600,tm800, tf900).