1623 range problem



I have a Furuno 1623 radar on my sailboat. Unit started to lose targets beyond 2 miles. Good target display on first sweep, 50% reduction on second sweep, then nothing. Local authorized Furuno service technician tested unit on the boat, said the magnetron was probably failing. He replaced the magnetron and adjusted heater voltage (was low by 0.5 volts). Re-installed radome on mast. Still has same problem as before. Works great at 1.5 miles. When changed to 3 miles, good target display for first sweep, second sweep much degraded, third sweep, nothing. What should I do?
I am waiting for a reply from the service tech. Some additional info: Internal Diagnostic check shows display unit OK. Scanner test shows Antenna Status "NG(0)". Tune bar is at bottom 20%. Strangely, distant targets will occasionally re-appear. Usually while adjusting the Contrast and Brilliance controls, but this may be just a coincidence as the controls are then left at their original setting. FTC is off. Gain and A/C Sea are both set at Auto - Moderate. A/C Rain is at 0. If distant targets are visible at 4 mile or greater, the display is stable to max range setting. But if I drop the range to 1.5 miles, and then increase to 4 miles, distant targets are gone. If distant targets are visible, and the unit is cycled to Stand-By and back to Radiate, the targets are still there. But if I turn the unit off and then back on, the distant targets are gone.
Thanks for your help and advice.
Per the manual it is normal for the selftest to show NG for the antenna the first go around. You must have the radar in transmit then run the self test twice to get a valid test on the scanner.

There are several things that could cause your reported issue. (like MIC, IF amp, display DU board) The problem does sound like a typical MAG going bad, so I can understand the thoughts of the service tech. Let us know how it turns out.
The service tech was unable to determine the cause, or fix the problem. Turns out the tech is not an Furuno authorized tech, and can not access the on-line only service manual. In fairness, he did not misrepresent himself. I assumed he was because he said he sells and services Furuno products. The boat is currently in the Puerto Vallarta, Mexico area, and there are no "authorized" service techs here that I am aware of. I will probably have to purchase a new radar unit, and have it shipped to me. It would not be cost effective to send a 10 year old unit back to the States for service and re-ship it to Mexico. Additional info: During one of many restarts and self tests, the scanner test said "OK(CF)", tune bar at 50%, and long range targets displayed at end of test. But when range was dropped to 1.5 miles, and back up to 4 miles, targets were again gone. No other changes or adjustments were made.
With you being outside the Furuno USA sales and service area; I have no access to the dealers who might be available for you.

You might contact the Furuno distributor for your area.

Acapulco No.35, Office No. 702 Colonia
Roma, CP 06700 Delegacion
Cuauhtemoc Mexico D.F

Phone: +52 55 5211 4372
E-mail: rdiaz@navalec.com
I have de same problem whith 1623.
In 2 milles setting de ecos disapears.

Can you tell me haw many hours the magnetro works ok
Magnetron life varies but they are rated for 3000+ transmit hours.
I wouldn't replace the magnetron without knowing it needs replacing. They can be costly.
I would recommend sending the unit in for repair evaluation.

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