Hopefully my last Leich901 issue - can only talk in one direction

[JacobCoffin]

Hi, I'm hoping this is just some dumb mistake I've introduced as I was finishing everything up, but I'm having trouble figuring out where and hoping maybe this is a common issue someone will recognize.

I have two Leich 901s I want to set up as a intercom. I've tested both and they worked, talked and rang each other even with bad temporary connections. I did replace one handset cord as it was badly frayed and had to be held at just the right angle to use it.

I've connected both phones to a RJ12 jack (I think one is a RJ11 jack but they seem to be the same?) so I can use regular telephone cords between them. My building already has a phone port in the kitchen and the phone wires run through the basement so it seems like the least invasive way to eventually link everything up.

But I'm testing everything before I start that and I've run into an issue:

The phone mounted to the display board can talk but can't hear the other one. Both can ring each other.

I've double checked the handset wiring, and I think it's right. I was careful and never dropped the microphone or anything.

I made sure the junction boxes link Red to Red, Yellow to Yellow, and Green to Green.

Am I missing something obvious?

One last possible clue: when I listen to the handset that can't talk and pick up the working one, I hear a click and it goes from silent to a very faint static hiss. When I listen to the working handset and manipulate the lever in the cradle of the phone that can't talk, I swear I hear the static when it's hung up, and it goes dead when I lift it off. But it doesn't pick up any noise while hung up either. I feel like this should tell me what the problem is but I can't see it, maybe it's not related.

Thank you!

[JacobCoffin]

Okay so I've tested a few more things:

I connected them directly the way I had them during testing (when they worked) and got no change.


I swapped the microphone from each handset and everything stayed the same, swapped the speakers, everything stayed the same.

One phone (on the display board) can transmit and the other one can hear it, but not the other way around. If I blow into the microphone on the display board phone I can hear it in its own handset but the same isn't true for the other one. The handset wiring all looks correct (as far as I can tell anyways), I might try swapping out the handset cord on the bad side to see if that's it, but I'm kinda stumped here.

Is there some known issue that causes this sort of thing? Capacitors going bad or something?

Thank you

[JacobCoffin]

One other bit of weirdness: when you hang up the display board phone, (the working one) the voltmeter connected to the talk circuit goes up slightly, but that's not the case for the non-working one.

Also when you press down on the cradle trigger for the display phone, like you're hanging it up, there's a loud click in its microphone.

But when you do the same thing for the other phone, you don't hear that, even though it's the one that can hear the display board phone.