|
|
Post by n4dxx on Apr 25, 2019 10:49:24 GMT -5
Just got a nice Mark IV..Good news the transmitter is 100% working..Reaceiver has an issue..I have tested all tubes and are in great shape..The s-meter does not fall back and the zero set does nothing..I hear no volume at all..Radio was re capped a while ago..The radio worked fine and after a while the receiver got weak and now the meter stay's fully deflected..Thanks for any advice
|
|
|
|
Post by 2600 on Apr 26, 2019 21:30:38 GMT -5
The relay can do this, if the contact that shuts the receiver down in transmit mode won't make the circuit while receiving. If your radio has the white-nylon plastic transmitter plug connecting the two units together, this is a failure-certain component. It will look like this before it goes bad.  The contact pins are just too small, and they will overheat from the circuit current. Turns the white nylon plastic dark. Browning corrected this error and used a more-robust "Jones"-type plug and socket made from hard black plastic with ten flat blade contacts on the transmitter-cable's plug. If your radio has the older one with the tiny round pins, it must be upgraded to the 10-pin Jones plug. Even if you have the upgraded connector, we see more and more of them that are mistreated. The shiny electroplated surface layer on the flat blades will get tarnished with age.  Any use of an abrasive or a knife blade to "clean" it will cause nothing but trouble. Once you expose the base metal of the blades, you will have to clean them constantly until a new plug is installed in its place. Smearing solder onto the blades will just damage the contacts in the receiver socket, and you'll have to replace both the plug and socket to get a reliable connection. There are other possible causes, but the relay and the transmitter cable/plug are where I look first. 73 |
|
|
|
Post by n4dxx on Apr 27, 2019 20:29:42 GMT -5
Mine has the clinch jones plug..i also put a jumper in to eliminate the transmitter per the service manual and still no joy
|
|
|
|
Post by 2600 on Apr 27, 2019 22:05:23 GMT -5
Umm, just on a hunch. Check R9, the 250 ohm 10 Watt resistor that runs from the B+ rectifier bridge to the 3-section "can" filter capacitor.
That one tends to run hot, and is an occasional, if not frequent failure. Would explain the symptoms.
Not the only possibility, but the "all at once" failure suggests the way wirewound resistors tend to fail.
73
|
|
|
|
Post by n4dxx on Apr 27, 2019 23:11:26 GMT -5
This one had a 125 ohm 10 watt but checks good..looks like its the wrong part..but worked fine before this..does not look at all overheated
|
|
