E470VA with a PLHH-Y009A - no power

[R_J]

Re: E470VA with a PLHH-Y009A - no power

It should be obvious you need to remove BOTH JW79 AND JW59 They are both connecting the same points. If by removing the BOTH and the short on the (+160VDC) line is gone, then the short must be with Q70x (can't make out the number) connected to EY7 & EY6
I will try to explain with this marked picture of the trace side of the board
Red = +160v line
Black = hot ground
Blue = JW79 & JW59
Grey = fuse

With JW79 &JW59 lifted, check the resistance between HOT ground and JW21, Is there a short?

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

It should be obvious you need to remove BOTH JW79 AND JW59 They are both connecting the same points. If by removing the BOTH and the short on the (+160VDC) line is gone, then the short must be with Q70x (can't make out the number) connected to EY7 & EY6
I will try to explain with this marked picture of the trace side of the board
Red = +160v line
Black = hot ground
Blue = JW79 & JW59
Grey = fuse

With JW79 &JW59 lifted, check the resistance between HOT ground and JW21, Is there a short?

With both jumpers lifted, yes there is a short between the hot ground and EY6/7. See attached, hopefully I tested the right items. See attached. I put the tested leads on the pins I tested.

[R_J]

Re: E470VA with a PLHH-Y009A - no power

One of those transistors must be shorted

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

One of those transistors must be shorted

So it's one of the transistors on the right, not one of the two on the left? Any way to test these without desoldering them?

[R_J]

Re: E470VA with a PLHH-Y009A - no power

So it's one of the transistors on the right, not one of the two on the left? Any way to test these without desoldering them?

Try checking them, but you will likely need to unsolder one of the drain or source leads to be sure.

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

Try checking them, but you will likely need to unsolder one of the drain or source leads to be sure.

I got EY7 off. How do I test it?

I got EY6 off, too. One of the items gives no connection between any of the legs. The other has a short between all legs. I guess the one with the short is the bad item?

[R_J]

Re: E470VA with a PLHH-Y009A - no power

Yes, the one is shorted, the location is Q70x. "one of the items" doesn't tell me which one, I need to know so I can see what else it might have damaged.
To get a short between Hot ground and 160vdc seems to require more than one shorted component. If the mosfet is shorted to all three leads, then it is possible the gate drive components may also be damaged.

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

Yes, the one is shorted, the location is Q70x. "one of the items" doesn't tell me which one, I need to know so I can see what else it might have damaged.
To get a short between Hot ground and 160vdc seems to require more than one shorted component. If the mosfet is shorted to all three leads, then it is possible the gate drive components may also be damaged.

One of the EY6/7 MOSFETs was shorted. The other was not.

EY5 (same type of MOSFET: KF5N50) was also shorted. EY4 appears to be OK.

Each shorted MOSFET was shorted on all 3 legs.

[R_J]

Re: E470VA with a PLHH-Y009A - no power

EY stands for Eyelet, NOT the component. I suggest you replace the shorted ones and then check the other components. If Q709 was shorted, I suspect it was Q708 that was also shorted. These are the mosfets that drive the backlight transformers.

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

EY stands for Eyelet, NOT the component. I suggest you replace the shorted ones and then check the other components. If Q709 was shorted, I suspect it was Q708 that was also shorted. These are the mosfets that drive the backlight transformers.

I checked all four. Two were shorted, two were not. Does this mean I just need to replace those two shorted ones, or is there another problem on the board that is causing the shorts?

[R_J]

Re: E470VA with a PLHH-Y009A - no power

I would check the diodes and the resistors as well

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

I would check the diodes and the resistors as well

I think I checked some of those in the prior posts. Any particular ones you want me to check?

[R_J]

Re: E470VA with a PLHH-Y009A - no power

I think I checked some of those in the prior posts. Any particular ones you want me to check?

You need to check the ones in the gate circuit, when the fet's short, they can supply the 160v from the drain, through the gate and damage the gate drive components, so if you replace the fets, and don't repair the gate drive, the fets will just short again.

[primuspaul]

Re: E470VA with a PLHH-Y009A - no power

You need to check the ones in the gate circuit, when the fet's short, they can supply the 160v from the drain, through the gate and damage the gate drive components, so if you replace the fets, and don't repair the gate drive, the fets will just short again.

Hmm could you be more specific? I'm not very good at electronics. Which parts are the "gate" components I should test?

[R_J]

Re: E470VA with a PLHH-Y009A - no power

A mosfet has 3 leads, a DRAIN, a SOURCE and a GATE, The "gate" of the mosfet has parts connected to it, check them.