[Collins] KWM 1 power supply question - Mystery Jumper

[Ian]

Greg,

I have no PS schematic but still have pages with the KWM-1 schematic on them
that I photocopied in the early 1960s when I had a KWM-1 that I wish I still
had as I'd added 40 meters to it and it worked great.

Pins 20 and 21 go to the contacts of the transmit receive relay.

Those pins are either opened or grounded depending on whether or not you are
in transmit or receive.

The diagram states, correctly, that Pin 20 is grounded on Transmit.  And
obviously pin 21 is opened on transmit and grounded on receive though it
doesn't say that.

If shorting the two pins together suddenly makes it receive I'd at least
look at the relay to see if something is strange about the contacts.
Perhaps somebody has made some modifications.  A bit of ohmmeter probing
should be worthwhile.

Ian, K6SDE


| -----Original Message-----
| From: collins-bounces at mailman.qth.net
[mailto:collins-bounces at mailman.qth.net] On
| Behalf Of Greg Mijal
| Sent: Tuesday, April 27, 2010 11:20 AM
| To: collins at mailman.qth.net
| Subject: [Collins] KWM 1 power supply question - Mystery Jumper
| 
| Howdy:
| 
| My recently acquired KWM 1 has been a tough one to mate to my home brew
power supply
| and wondering if anyone knows the answer to this situation.
| 
| Previously:
| All filaments light up ok and 260 vdc applied to the B plus line.  Current
draw is correct per
| spec's but no receive, no nuthin'.
| 
| Today: I spotted something in manual that does not appear anywhere else in
the manual.
| That is, the AC power supply schematic shows a jumper from pin 20 to 21 on
the connector.
| 
| I put the jumper in and the receive began to give the standard hissing
sound.
| Looks like the jumper enabled something in the radio but the Collins
manual doesn't seem to
| have an explanation.
| Can someone tell me what this jumper's electrical function is?  If I
missed it and it's in the
| manual, what page do I go to?
| Thanks
| Greg
| WA7LYO
| Kinston NC
|