JRC1500 radar - no sweep - why?

[concentrik]

The display is OK and shows everything it should; all the controls work. The scanner is rotating but there is no sweep displayed on the LCD after going from standby to xmit. Any suggestions (except bin it - it's this one or nothing!)

Thanks.

 

[Sandyman]

Have a play with the brightness & contrast set up.

 

[concentrik]

Have a play with the brightness & contrast set up.

No probs there, both controls work as they should but no amount of adjustment will reveal a sweep...............

 

[Sandyman]

ang on i'll go flash mine up see if I can remember what I did when I had the same problem....................back in a mo

 

[Sandyman]

Have you set gain control to low ? what range are you on ?

 

[concentrik]

Have you set gain control to low ? what range are you on ?

Sorry I'm not making myself clear... it's not just that there is no return displayed - there isn't any rotating sector in the display. Apart from the static items like legend, range rings, EBL etc there is nothing shown. Range is max, gain is max, sea clutter reduction min, same for rain. None of these will produce a trace when adjusted anywhere.

 

[earlybird]

Have you actually looked at the scanner rotation? When my Furuno did something similar, the drive belt had come adrift. The motor was getting power, but the antenna wasn't turning.

 

[Sandyman]

Okey Dokey

You said ''The display is OK and shows everything it should'' so I assumed you meant that you just couldn't see the sweep on the display

So you are not seeing any returns !!! not even any clutter !! hum.................you have checked the plugs on the back are fully home & tight ?

Tried switch off & back on ? Checked input voltage ?

 

[concentrik]

Have you actually looked at the scanner rotation? When my Furuno did something similar, the drive belt had come adrift. The motor was getting power, but the antenna wasn't turning.

yes, just checked under the dome.... the scanner is rotating. Also, we have a SEAME active radar reflector, which has always been triggered by the JRC.... when I activate the radar, the SEAME indicates that it is receiving radar signal...... any other suggestions welcome...

 

[Roberto]

..... any other suggestions welcome...

It's likely to be a faulty magnetron, especially if the radar has been used a lot or sporadically..

 

[AntarcticPilot]

It's likely to be a faulty magnetron, especially if the radar has been used a lot or sporadically..

Surely not if his SeaMe is detecting a pulse.

 

[Martin_J]

If the magnetron were faulty then I would not expect the Sea-me to pick up the transmissions.. Perhaps they are just weak though..

I don't have experience of the JRC but in Raymarine kit there is a small sensor in the radome that detects the spin of the rotating scanner.. The display needs this rotation feedback information in order to know which way the scanner is facing at any point in time. Without this information, the magnetron does transmit but the display does not know the scan direction thus displays nothing.

Is there not a hidden diagnostics menu available in the display that might show results of component tests (and of scan rotation times)...?

 

[Sandyman]

Surely not if his SeaMe is detecting a pulse.

Could still be tx'ing on v low power and the SeaMe being so close would still detect a pulse ?

 

[Martin_J]

Moving on from the post above... the spin timing information is probably sent over just one of the return wires.. Has the cabling been checked (especially at any joins at the foot of the mast)?

 

[concentrik]

Moving on from the post above... the spin timing information is probably sent over just one of the return wires.. Has the cabling been checked (especially at any joins at the foot of the mast)?

Yes there is a sensor mounted on the scanner support, clearly visible, which seems to coincide with a small magnet on the underside of the scanner. So I'm guessing this would provide a timing pulse to tell the display to start the 'raster drawing' sequence. And without this timing pulse the sequence may not start, hence no image. I only have a DMM here at the moment so may not be able to follow this pulse through.

Can anyone point me at a service manual?

As a side issue, can anyone tell me how the information about target returns is sent back to the display? Is it a digital data stream or an analogue signal? And how does it carry distance and intensity information?