Hitachi/Planar JM777 flickers and dies when plugged in

[nubie]

I have a Hitachi JM777 (also a Planar of the same type, don't recall the model # right now).

The Panel led will flicker once green when I plug it in. If I put an electric heater on the back of it near the power cord the duration of the green will increase to about 1-2 seconds and you can see the backlight try to start. If I leave the heater on it long enough (maybe 10 minutes), it starts and works great, until it is turned off again.

I have a spare power board with a blown backlight section (arcing has pretty much eaten the board). So I pulled the jumpers to the inverter up on both boards to test only the low voltage section.

I get 12-16V and 5 volts on the good board (bad inverter), and I can see the LCD is working with a flashlight. On the bad board it will be 12-16v and 5volts until the LED flickers green, then it drops to 1.2v on both lines.

(I have a spare input-logic board and it acted the same way with the power LED when I swapped them.)


Here are front and back pictures of the power board. I can take better ones if needed, I didn't set up a proper light source or use a tripod for these.


What should I test or swap on this board to get it working?

[seanc]

Re: Hitachi/Planar JM777 flickers and dies when plugged in

Bad solder joint or caps.

Check for any bad joints, re-solder the transformer joints.

[nubie]

Re: Hitachi/Planar JM777 flickers and dies when plugged in

I have re-flowed all of the transformer joints and the IC joints, also most of the AC side through-hole components.

I suppose I could start transferring everything over bit-by-bit, but I would rather test for the bad component first.

How do you test the transformer? I don't know how to read it, I just know that when testing across the sides of the dual-diode package I am seeing 12-15v, but before that I can't pick up any voltage (when tested against ground, or against the other outputs on the transformer)

[pedro]

Re: Hitachi/Planar JM777 flickers and dies when plugged in

I have a Hitachi JM777 (also a Planar of the same type, don't recall the model # right now).

The Panel led will flicker once green when I plug it in. If I put an electric heater on the back of it near the power cord the duration of the green will increase to about 1-2 seconds and you can see the backlight try to start. If I leave the heater on it long enough (maybe 10 minutes), it starts and works great, until it is turned off again.

What should I test or swap on this board to get it working?

The ESR of aluminium electros drops as the temperature rises. Any time I see gear that starts better warm than cold I immediately suspect the caps are on the way out. I'd check the ESR. If you don't have access to an ESR meter, I'd replace the caps anyway.

[nubie]

Re: Hitachi/Planar JM777 flickers and dies when plugged in

OK, I swapped all the caps from the low voltage section on the one that worked over to the one I started with.

Worked fine on the low voltage tests so I connected back the backlight inverter jumpers and it works great so far. Time will tell.


Thanks

[xqoliver]

Re: Hitachi/Planar JM777 flickers and dies when plugged in

Hi I have same problem, do you remember which Cap you swapped? Many Thanks