1734 radar magnetron issues



My radar strangely just randomly stops working. I can see the sweep and tune to get black dots but no returns. It works fine then doesn't. It's done this twice in the last two years. Here's the frustrating part-after turning it off and on over a period of a couple days, it starts working again. Comes back slowly each time it's turned on and finally full strength.

Its a model 1734, with a 7" NavNet plotter, about three and a half years since installation. I've checked all the connections and they are tight and clean-including in the magnetron.

Any ideas? It's disconcerting that it "might" decide to not work just when I really need it.

When the problem happens; have you tried to manually tune the radar to see if you can get the targets to come in?

It could be an auto tune problem or a problem with the MIC. Magnetrons don't work, not work, and then work again. They go bad like a light bulb going dimmer and dimmer until you get no targets. Longer range and smaller targets get hard to pick up as the magnetron goes bad/ages. The Modulator board that drive the Magnetron (when it goes bad) normally works great one day and then nothing the next and never returns back to life. To me, your problem sounds like something on the recieve side of the scanner or the SPU board in the display that processes the data.

Intermittent problems are the worst.
I always tune manually. When it quits, I can tune the gain all the way up and nothing except the black dots and I can see its spinning. When it comes back, gain is normally at 72-74. Others set to zero unless I need them.

Also, when it comes back, at first the echoes are weak and only close ones register. Then the more I cycle the whole unit (chart plotter full reboot) off and on, the stronger the signals get and the more range. This happens over four or five off/on cycles.

The only other possible correlation is: it first happened crossing the itcz during severe lightning and rain. We never took a hit though and none of the other equipment was affected, but it stopped working for almost two weeks before coming back a little at a time per above. Then it worked fine for a year and a half but quit after a very heavy rainstorm a couple weeks ago. Was down for a week and now has come up again. As I noted though, I've checked all the connections and can find no wet or corroded connections. Just weird.

Frustrating as I'm in Fiji cruising, so don't have access to techs to look at it.
When you manually tune the radar does the tuning bar change up and down?
What is the hightest point on the tuning bar during normal operations?
You know I confused Gain (which I use all th time) with Tuning (which I forgot was even a function I had control over). I have not touched the tuning, but it was on manual. I just tuned it to max and got "193".

What does Tuning do and is it possible that having it on manual but not changing it is why it has gone out twice and then come back?

Funny, I know how to operate all the functions but completely overlooked tuning since three years ago when I originally set it up.
(Not sure if the last post made it)

I confused Gain with Tuning.

I always adjust Gain, but have not adjusted the Tuning since I set up the unit three years ago. It was on Manual. I just tweaked it and 193 was the value when the bar was highest.

Is it possible that not touching this is why I "lost" sensitivity and then after a while it came back? What does the tuning function do? There's no explanation in the manual.

Think of auto tuning (default) as a pre-set of your favorite radio station using an older car radio. You hit the pre-set and the radio is playing your station. Manual tuning is like running the dial back and forth and tuning in the station yourself. Sometime if a radar has a problem with the MIC (tuner) or auto tuning (controlled by display), you can manual tune in a good signal when the auto isn't. Another thing that sometimes happens is the MAG (transmitter) can get noisy, as it gets old, and it might have side lobes (transmissions) that your "auto" tuner is locking onto by mistake. When you manually tune, you can tune past this and find the real signal bring in good targets. In your case, it would allow your radar to work until you find a better place to get it fixed.

The tuning number you talked about really isn't important. Normally you want to tune up and down until you can lock on to the radar signal and pull in targets. The tuning bar up at the top normally will peak out at about 75% when you are on the main return signal. If you can't get the turning bar to peak or get good signals then your MIC or MAG has a problem. Based on what you have said, I would lean towards the MIC because a MAG normally wont do what you describe. If you can tune in good targets, then you can address the issue later but it could be the MAG, MIC, or the SPU board in the display. It would need a good tech on the boat. (or send the unit into service)
It tunes to 193. I haven't been tuning it since the original set up three years ago and it's set to manual. Could that have been why it's sensitivity seemed to drop but then came back. I'm not familiar with what tuning does. I use gain, sea-clutter, etc all the time, but haven't tuned. What does it do in the radar and why does it need adjustment.
Thanks very much. Sorry for the extra reply, I didn't see yours.

OK, I've got it tuned and its working great. Many thanks for all the help. I think I'll play with setting it to auto tune and see if that works, or whether I'm tuning around some issue and then I'll have a tech look at it when I'm in New Zealnd this year.

Again, many thanks for the excellent help. You and it's board are really helpful. Much appreciated! :furuno