No Power on AM-1780

[mm58]

Hello,

I have an AM-1780B that will not power up thru the J508 connection.
It does however power up thru J501.
Any ideas? Is there a common failure point that might be the issue? Or where might I look?

Thanks in advance...

Mike

 

[Wile E. Coyote]

Hello,

I have an AM-1780B that will not power up thru the J508 connection.
It does however power up thru J501.
Any ideas? Is there a common failure point that might be the issue? Or where might I look?

Thanks in advance...

Mike

What's your Installation Switch set to? If you're trying to feed power up through J508, the Installation Switch has to be INT ONLY. Powering up as part of a radio installation (i.e. through J501) it has to be set to OTHER.

If you feed power to *J508* with your Installation Switch set to OTHER - bad things tend to happen. It's been a long time but from what I remember it will burn off one of the rotary switch contacts quite spectacularly, as essentially it arcs 24V+ to Ground.

Always set your Installation Switch *first* - then cable it according to that Installation plan. Never, ever, ever change the Installation Switch with power applied to the system.

 

[mm58]

What's your Installation Switch set to? If you're trying to feed power up through J508, the Installation Switch has to be INT ONLY. Powering up as part of a radio installation (i.e. through J501) it has to be set to OTHER.

If you feed power to *J508* with your Installation Switch set to OTHER - bad things tend to happen. It's been a long time but from what I remember it will burn off one of the rotary switch contacts quite spectacularly, as essentially it arcs 24V+ to Ground.

Always set your Installation Switch *first* - then cable it according to that Installation plan. Never, ever, ever change the Installation Switch with power applied to the system.

Thanks for the reply.

I did open the back and found two blown capacitors under the "RADIO TRANS" switch (upper right). I successfully replaced the caps, but there was
some carbon and a tiny but of melting to a ribbon trace. Best I can tell, none of the actual traces were affected. So I'm back to square one. Good thing is I know it works, but just needs power thru J501.

Mike

 

[papakb]

Find a copy of TM 11-5895-1548-34. That'll help explain what's happening.