Model 1935 powers off after starting to rotate

[jennyleigh]

I have a model 1935 with very few hours. After power up when I press transmit the radar will rotate and show returns but after about 1/2 of a turn it will shut off and re-start. The array 0070 feels free by hand. All connections are good and voltage good. RTR-064A. Are there any next step troubleshooting I can try? Thanks

 

[Johnny Electron]

We haven't sold the 1935 in about 4 years so it sounds like it hasn't been used much if it has low hours. It isn't good not to run radars as sitting can be worse than using them. Being that it start turning, the motor start circuits are working. It sounds like a lack of current. The unit starts but can't get enough current so it is shutting down. You might want to check all the connections for corrosion particularly because it has been sitting. Corrosion on the connector plugs for the motor or on the supply power cable or at the back of the unit on the pins could restrict current. It is important to check the power source as well. You might try connecting it up to a bench type power supply to bypass the source power. Are you getting any error on screen at all? Like no BP or HP?

 

[jennyleigh]

Johnny,
Today I used a different battery, power cord and used a 139 I had and connected to the array.
Same symptoms exist, the array turns a little more than half a turn and then shuts the 139 unit off.
I tried to assist turning by hand but made no difference.
It seems after the array rotates about half a turn is draws a significant amount of current and the unit shuts down.
It is free to spin by hand when the unit is off and a slight drag when the unit is on but not transmitting.
The signal cable to the array is in good condition and all connections clean.
No error on the screen, just shuts down as if low voltage.

 

[Johnny Electron]

Have you ever tried to push start the antenna by having someone push it in the direction of rotation while someone hit TX at the display? This is a good way to see if the motor start is working but too slow.

 

[jennyleigh]

Johnny,

Yesterday we spun it by hand, then hit the TX while still hand assisting the rotation.
It didn't stay on any longer than without assisting before the unit cut off.

If I remember correctly it always spun slow at first and then after about a half a revolution you could hear it speed up.
This unit cuts off about the same time it would have previously sped up.

Thanks for your help!

 

[Johnny Electron]

One must have an FCC licence to work inside a radar so it is would be time to call a qualified dealer. At this point I suspect that there is something wrong with the modulator board. As you go to TX the display sends Transmit trigger and voltages to the scanner. The unit start the process of turning but as the modulator begins to build high voltage needed to fire the magnetron, a shorted FET or other issue is encountered and shuts the radar down. A dealer can try to internally isolate and verify. Another option would be to pull the RTR out and send it to the service center. They can repair it and send it back. Many dealers will likely do this as well rather than try isolating it in the field.