Radar Troubleshooting

[Reefmagnet]

Hi All. Our boat has an ancient JRC 8Nm range radar that isn't working properly. The screen blacks out unless the rain clutter function is activated. With the rain clutter function on, I can adjust the unit for a legible display for the lowest - 0.25 Nm - range, but can't get any sensible display for higher ranges - only speckles and clutter. I'm thinking that maybe bad bearings on the radome unit could cause this problem? Anyone able to take a stab at this or other possible causes? Cheers.

[ka4wja]

Dear Reefmagnet,
Honestly, I never knew that JRC even made a "8nm range" marine radar, as the smallest one I've ever seen is their old JRC 1000 (which was only a 1.5kw peak unit, w/ a 12" radome), that was spec'd as a "16-mile unit"...

But, in any case, have you contacted JRC directly or an Australian servicer??
JRC Marine Electronics

TMQ International



as for what could be wrong....on a unit that old, it could be anything...and it's doubtful it is actually worth spending much money on it, especially as magnetrons have a limited lifespan, and depending on your units actual age and number of hours used, you may have already passed that timeframe.....but, in general...

Originally Posted by Reefmagnet

The screen blacks out unless the rain clutter function is activated. With the rain clutter function on, I can adjust the unit for a legible display for the lowest - 0.25 Nm - range, but can't get any sensible display for higher ranges - only speckles and clutter. I'm thinking that maybe bad bearings on the radome unit could cause this problem? Anyone able to take a stab at this or other possible causes?

My first thoughts are:
a) display/processor intermittents/failure...
b) receive unit failure...
c) wiring/connection problems..
d) transmit/magnetron failure...


Never heard of bad bearings, but depending on the exact age and number of hours used, it's a possibility....although, I doubt they are the cause of your troubles...



That's the best I can come up with, with the limited info I have...

Fair winds..

John
s/v Annie Laurie

[Reefmagnet]

Thanks ka. Yes, you are right; The range selector refers to the ring radius spacing and there are two rings on the display. The radar is a JMA-2011 very old LCD display model. I agree too that the radar is not worth fixing if it is even moderately broke as I really don't have use for it at the moment except as a curiosity and to learn on. I was out at the boat tonight and played around with the radar settings. I guess the best problem description I can give is that the either the receiving side of the unit has become hypersensitive or there is a lot of noise being generated during transmission. I think it is the latter, as playing around with the rain clutter filter activated does provide a valid display of sorts on the screen. With rain clutter deactivated, the display just becomes saturated with noise as it draws the sweep. I don't think the unit has had a lot of use in it's life as the boat has spent most of it's time in the same region and radar is just not that important a tool around here. Of course I'm only guessing, but the unit's key pad is in as new condition which is usually a good indication of prior use. The radome drive is quite noisy, almost "graunchy" in operation and it is making a cyclic variable noise rather than a constant drive noise that I would expect (although I've never heard how a "good" unit sounds so I'm only guessing again.

I'm aware of TMQ, but they don't even have a manual listed for this unit and I'm certainly not inclined to throw much, if any, cash at this. I think I'll strip it down and clean the contacts and lube the bearing system and see if there is any improvement as I figure I it owes me nothing anyway.

[ka4wja]

Reefmagnet,
With this new/additional info..

Originally Posted by Reefmagnet

The radome drive is quite noisy, almost "graunchy" in operation and it is making a cyclic variable noise rather than a constant drive noise that I would expect (although I've never heard how a "good" unit sounds so I'm only guessing again.

I think I'll strip it down and clean the contacts and lube the bearing system and see if there is any improvement as I figure I it owes me nothing anyway.

I'd say your plan looks good to me!!!

From what you write, it even possible that the antenna array isn't "pointing" correctly while the unit is attempting to rotate/scan...

Have a look, clean and lube the mechanics....and check, clean, and tighten all the connections in the radome as well as any "dis-connect" plugs you may have (most boats with mast-mounted radars have a dis-connect plug at the mast base / in the bilge to allow for easier pulling of the mast)...


Good luck an d Fair winds...

John
s/v Annie Laurie

[socaldmax]

Have you done a ring time measurement? This is a measure of the transmitter's power out and receiver's sensitivity, in addition to giving you an idea if the transmitter and receiver are still tuned to the same frequency. This is a periodic test performed to give the operator an overview of past, present and predicted future performance based on how slowly or quickly the ring time is decreasing.

If your manual doesn't have the procedure, you can find a generic copy online.

Based on the age of the unit, I wouldn't be surprised if the transmitter (magnetron? klystron tube?) is dying or dead, but who knows. I just replaced a 12 yr old car battery, and I'm still in shock!

[Reefmagnet]

Thanks again guys. socal, where would I find info on doing this ring time measurement? I don't have the manual for the unit and know little about radar in general. Cheers -Jeff.

[Outwest34au]

Hi Reefmagnet,
I have a JRC dome in the shed with an uncut cable and pretty sure I have a book of sorts there also. I'm just down the road from you at the Gemfields so if you needed to borrow either it's no biggy.

Cheers,

[Reefmagnet]

Hey cool Outwest. Thanks for the offer. Weather permitting, i'll be taking the radome unit off this weekend so I can bring it home and tear it down (thankfully it's mounted to a stern pole, not the mast). I'll keep you posted. Cheers, Jeff.

[ka4wja]

Reef,
Take Outwest up on his offer on borrowing the cable / manual, etc...
But, remember that a radar unit is not something for laypersons to mess around with...they can be dangerous to work on...



And, with respect to socal, you do NOT have the test set, echo box, nor other more modern equipment (nor the expertise) to do the tests he recommended..

Originally Posted by Reefmagnet

socal, where would I find info on doing this ring time measurement? I don't have the manual for the unit and know little about radar in general. Cheers -Jeff.

And, in all honesty, even if you did have the equipment/test sets, etc, if the radar is not operating, a ring time measurement is not possible....


Reefmagent, PLEASE have due respect of the radar transmitter and scanner, and do NOT attempt any testing with the unit ON (transmitting), as it is dangerous...(not specifically talking about the magnetron voltages, but the invisible microwave radiation that can blind you!!!)
Bottom line here is this is one reason why you do not find many DIY radar troubleshooting/testing info on-line....'cause those that know, know that it isn't something to fool around with...


If you can't find obvious problems (wiring, connections, mechanics, bearings, etc.) and the manual provides no further insight, and use of the borrowed cable doesn't solve your troubles....your only real options are:
--- scrap it...
--- hire a professional to repair it....(not my recommendation)
--- buy a new radar (if you need radar)




Sorry to be so blunt, but I do hope this helps...

fair winds..

John
s/v Annie Laurie

[Reefmagnet]

Thanks for the heads up ka. I do have electronics quals and am aware of the dangers of high voltage, low impedance magnatrons and the microwaves they produce (but that's about the limit of my radar knowledge!). I am going to limit myself to cleaning and lubing only hence why I intend to remove the radome and bring it home to service it. I'm keen on using radar as an overlay onto ECS charts for navigation, which this unit can't do which means even if it worked fine I'd be replacing it down the track regardless if we end up using our current boat as "the boat" for full time cruising.

[socaldmax]

Originally Posted by Reefmagnet

Thanks again guys. socal, where would I find info on doing this ring time measurement? I don't have the manual for the unit and know little about radar in general. Cheers -Jeff.

Here is a link to one online, but as John pointed out, if the radar doesn't have an echo box and a directional coupler, it may not be possible to perform it. We used to perform this and log the results prior to every underway and we could track how rapidly the transmitter was losing power.

http://www.navymars.org/national/tra.../14190_ch4.pdf



As John pointed out, be VERY careful of getting radiated. I'd secure all power sources to it before doing anything, and be careful of any stored power in the power supply caps.

I was trained to operate and repair US Navy radars, and we operated Furunos as decoy radars, but I have no experience with that brand, sorry I couldn't be more help.