radar repair

[Charlie]

I went to turn on my radar the other day and the screen turned on but there were no targets. I went thru the manual it said to check and see if the magnetron was set to spin. I checked and it was. The other thing it said to do was to check the cable? How do you check and see if the cable is ok? Am I going to need to bring the radar to a marine electronics tech?

[Mule]

Disconnect your cable to your radar on both ends and check with a VOM to see if it is open or grounded to the shield. I assume the cable is coax.

[Charlie]

Originally Posted by Mule

Disconnect your cable to your radar on both ends and check with a VOM to see if it is open or grounded to the shield. I assume the cable is coax.

It is a thick cable with about 12 ormore wires running thru it. As I understand it it runs a number of different operations in the magnetron.

[Mule]

Then I assume it is a plug in..short two colors on one end and test for short on the other. You need to prove continuity. Most of the time cable problems are termination problems. Examine as much of the cable as you can so as to look for damage. This may not be a cable problem.

[GordMay]

Cable Continuity:
To perform a continuity test on a cable, set the multimeter to test the lowest possible ohm scale (Rx1) and work your way up. Attach the test probes to matching wires (or connector pins) within a cable, and the resistance will drop to near zero if the cable is good, or towards infinity if it is open.

When the probes are disconnected from the cable, the multimeter will display infinite (high) resistance. On an analog meter, the pointer will remain on the peg at the left end of the scale. There will normally be an infinity symbol at this end of the scale. (On a digital multimeter, infinite resistance is often indicated by the numeral 1 without a decimal.)

[Charlie]

thanks I'll see if that is possible

[s/v Jedi]

Switch the gain to manual and increase it slowly. If targets show up before the screen becomes one big target, it's the magnetron that needs to be replaced. I'm there too ;-)

cheers,
Nick.

[Charlie]

Originally Posted by s/v Jedi

Switch the gain to manual and increase it slowly. If targets show up before the screen becomes one big target, it's the magnetron that needs to be replaced. I'm there too ;-)

cheers,
Nick.

I can see the range lines etc but I don't see any targets. The radar does not have many hours on it. Under 1000. I'll have to check the gain again but I think that was the first thing that I tried.

[Hampus]

Does the radar tune? I assume you use auto tuning now? So, is the tuning bar blank or is it partially filled? With only 1000 hrs, it's unlikely that the magnetron will have to be replaced due to wear, it's more likely you are suffering from error due to lack of use. Corrosion etc. If your hearing is still intact, the fastest and easiest way to check if the radar is transmitting is by listening to it. Set it to a scale > 24 miles and go listen, keep your head under the radome, about 2 feet and you will hear a very ditinct high pitched continous beep.

There could be a hundred problems but corrotion and a bad connection is the most likely. Good luck!

By the way, what kind of radar is it? Brand, model and year?

/Hampus

[rexposeidon]

You said you can see range rings (and I assume you can adjust them) can you see the sweep?

[Charlie]

The radar is a 36 mile furuno. It was installed two owners ago in what looks like a good maner in 1996. I can get you the model # later today. I tried both auto tunning and manual tuning and was not able to get any targets. I cannot see the sweep. I just remembered something. When installing some other electronics i had to remove the CRT. while working on the other electronics the CRT hung from its wire for a matter of ten seconds or so. It was a short fall maybe a foot and the way the wires are zip tied it did not make a pull directly on the plug. The fall did not make a loud noise I just sort of noticed it so I don't think that it was violent but it could have been enough to upset the wires. How can I test the cable?

[Hampus]

Originally Posted by Charlie

I cannot see the sweep.

No sweep and no noise? Then you're not getting any video from the antenna. The fall of the CRT could have something to do with it. Check the cable for continuity. Also check the radome for oxidation.

/Hampus

[senormechanico]

As a retired electronics tech, I agree with Hampus . You have no video reaching the CRT. Look for a bad connection most likely a shielded cable in the connector. It's possible it could be a circuit board break in the display where the connector mounts to the board.

Steve B.

[Hud3]

I'd suspect the cable, too, but I had those symptoms appear on a one year old Raymarine radar. It turned out the the tech that installed the radome set it down flat on the SS mounting plate on the pole and thus blocked the weep hole. That allowed condensed moisture to collect until it ruined the innards. They gave me a new radome at no charge.

[Charlie]

I'll do a close inspection of the cables. As far as checking for continuity how would I do that? From the manual it looks like there are 29 pins that are connected thru this cable. I would need to run a wire from one end of the cable to the next and then have some kind of small probe that would fit inside the connectors. Is there an easier way? If I brought the CRT unit to a furuno dealer would they be able to bench test it for me?