[Elecraft] K3 key-out jack - configuration needed?

[Oliver "Olli" Dröse]

Hi guys,

preparing for the autumn contest season I thought to do some cable work today. 
Made up a cable to key the amplifier and wanted to use the key-out jack therefor 
(only need to sink 13,8 V / 60 mA so should work perfectly well). But the amp 
isn't keying. So I measured the RCA jack and unkeyed I can measure infinite 
resistance as it should be the case but if I ptt the radio no change on the RCA 
jack?! Should be around zero then so no keying there.

Checked the manual but couldn't find anything related to configuration of that 
jack, seems it should be always working, right? Any ideas why it is not?

Checked the LP key-out on the ACC connector and that is working properly (but 
not enough for the amp, ofcourse, only measured there for verification the radio 
is really keying out, hi).

Can anybody help?

TIA & 73, Olli - DH8BQA