V72-Polarity Switch issue

Trying to repair a v72 rack job. Seems like at least a semi professional build.

Both preamps sound great. The problem is with the polarity switch. When engaged the gain drops and becomes distorted.

The polarity flip is on the input and appears to be wired correctly. I've attached a quick sketch of the input.

+48v switch ties into the switch via 6.8k resistors.

Any idea what might be causing the problem? Source is balanced; cables are balanced. Scope confirms what I was hearing.

Thanks for any input!

forgot the sketch... I should point out that I think it should be working. Can't see why swapping hi/lo would not function the same. Could the input transformer be wired incorrectly?

That looks OK, problem is probably after the switch...

Inject a signal one leg at a time, single legged signals to + input and - input should behave the same just reversed polarity.

JR

Yea I started poking around a little and then just said screw it. Rewired the pol. flipv to be on the output. Works now and the wiring is tidier. I am a little curious as to why it wouldn't work. I'm not very familiar with the v72 modules but I assume the input transformer is to blame

..a short to ground in input transformer primary could do this..?

I hope the 48 Volt is coming on slow , otherwise you will kill the input transformer...  ( if it isn’t  already )

( the transformer-wire is PVC coated , rated for approx. 24 Volt top and old... )