1712 no targets after second turn

HerveOz

New member
Hi, I have a Furuno 1712 with a radome RSB-0087 RTR068. It worked fine until it started to lose all the targets including land after the second turn.
When I change the scale, sometimes it picks it all up again for one turn and they disappear.
I removed the lid, the antenna turns fine and I cleaned and greased all the connections which made no improvement. In some rare cases it works fine for a few minutes and then it plays up again.
I was told it is probably the MIC that is faulty, is there anything else that could cause this fault?
I love my radar and would like to fix it if possible. The MIC is S-RX350 / RU-9458 and the Magnetron E3588.
I found a second hand "new never mounted" radome RSB-0071 RTR057, is it worth purchasing this unit and stealing parts of it if they are compatible, please?
 
I would not suspect the MIC based on your description. I think it is more simple than that. I would expect that the reed relay (000-142-465) is worn out. I would try that before going too far.
 
Thanks Johnny for the quick reply and suggestion. Could you please explain to me the function of this relay and its location please? Is there a way to "bypass" it for testing purposes?
 
The relay in the dome normally on a small aluminum standoff. You will find a small magnet on the bottom of one end of the array that turns. This magnet will cross over the reed relay and switch it once for ever radar rotation. This creates the heading pulse. You can test it with an ohm meter but it is hard to know for sure when it is intermittent. The switch should short each time you take the magnet across it. The radar needs this signal to start where the redraw of the radar begins and ends. It is a wear device and over time get worn out and doesn't always close or open as it should.
 
Hi Johnny, Thanks for the explanation and advice. I measured the resistance of the reed relay and I consistently get 58 Ohms when the magnet of the antenna is present in front of it whilst still connected to the rest of the electronics, about the same when disconnected. I thought the internal resistance of the reed relay contact might have been a bit high so I disconnected it and replaced it by 2 wires which I was briefly connecting to each other at each rotation of the antenna (standing well above the radar to avoid being blasted by the microwaves). I understand the time could not have been very accurate and the redraw of the radar screen wasn't perfect but same deal, after a few turns no more targets, just a few random echoes on the screen. When the reed relay or my temporary wires were disconnected or not "activated" at each turn, an error message appeared "missing heading sensor" or something along those lines which I understand is normal. I also found in the manual a procedure to calibrate the voltage supply to the magnetron heater, I measured 7.99V and adjusted to 8.01V just for the sake of it but it obviously didn't make a difference.
Do you have any other ideas to try to troubleshoot my problem, please?
I really appreciate your help and expertise in trying to help me out with this issue.

Cheers,
Herve
 
If you have an oscilloscope, check to see if you get the 360 bearing pulses coming down the BP line from the scanner.
 
Hi Johnny, we have a lot of tools on board but an oscilloscope isn't one of them unfortunately and we are quite remote from "civilisation". Is there any additional test I could do? If you don't believe there is more testing I could do to isolate the problem, I will start looking for second-hand parts for the radome what would you start with please?
 
I would start with the reed relay, then the motor, then it becomes more of an issue with the SPU board in the display or the INT board in the scanner. Good luck.
 
Hi Johnny, I found a second hand radome, I was hoping you could confirm if the parts and circuit boards are compatible with mine please? It's a 13" RSB-0093 RTR074. The MIC is RU-9458C (mine is just RU-9458) and the magnetron is the same as mine, E3588. I understand the antenna is shorter than mine but it "looks" like everything else is the same.
 
Hi, It's now fixed so I thought I would share it on the forum in case someone else has the same problem. I replaced the reed relay but it didn't improve it unfortunately.
I bought a second hand MIC (RU-9458) and it fixed it straight away.
The targets were so "dark" that I had to significantly decrease the gain setting and it looks perfect now. Having to increase the gain more and more could maybe be a sign that the MIC is getting tired? Probably something I should have mentioned at the start to make the troubleshooting easier but I only had the boat for a year and the gain setting was already high and I thought it was normal. Thanks Johnny for spending so much time trying to explain and fix it remotely for me.

Cheers,
Herve
 
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