Westinghouse Black screen W4207

[CraigR]

I have a Westinghouse W4207 that a guy brought me after he tried to fix it. The story is that the TV was dead totally and he replaced some caps on the power board that were bulged. The set now gets the green light on front when the power button is pushed and I see LED's light up on the main board and I also get 400volts on the main cap but the screen remains black. No flash of the back lights no menu or anything. Not sure what to check next.

[jetadm123]

Re: Westinghouse Black screen W4207

The wiring harness in your third photo has a number of cut wires. What did those connect to?

Post a photo of the inverter assemblies (covered by metal plate on each side of TV). Are they getting any voltage from the power supply? You should see something like 24V.

[CraigR]

Re: Westinghouse Black screen W4207

I seen those cut wires and the guy swears he did not cut anything and I don't see anyplace they may have gone. The harnesses all look ok and I do not se anything that may have taken a plug. I am getting 24volts at the inverters by the fuse when It's turned on.

[jetadm123]

Re: Westinghouse Black screen W4207

Looks like they have been worked on. Check fuse on both inverters. If blown, then check the 4 large mosfets for shorts.

[CraigR]

Re: Westinghouse Black screen W4207

Already checked fuses and are ok.

[jetadm123]

Re: Westinghouse Black screen W4207

Are those the original mosfets on each inverter board? Looks like they were re-soldered/replaced?

Try checking the secondary winding resistance of each inverter transformer & compare values.

Also, are any of the pins on the wiring harnesses marked something like BL_ON (also look underneath each board) on the inverter or mainboard?

[CraigR]

Re: Westinghouse Black screen W4207

It kind of looks like someone tried to touchup the solder on the tops of the mosfets but the connector part looks normal.

[CraigR]

Re: Westinghouse Black screen W4207

Readings for the windings are about the same. I had a spare bulb and un-pluged each one and tried it. Still no luck but on a couple I got a very short flash on the bulb but only an inch or so coming from the Master side.

[budm]

Re: Westinghouse Black screen W4207

ON/OFF pin on the left of the large white connector.
https://www.badcaps.net/forum/attach...8&d=1427835294

[CraigR]

Re: Westinghouse Black screen W4207

Am I correct in thinking that if I get a steady 24volts at the inverters they should fire up unless one or both are bad?

[budm]

Re: Westinghouse Black screen W4207

It needs 24V + BL-ON command signal, and sometime may also need the DIM command signal.
The MASTER/SLAVE Inverter boards setup as push-pull, if the Slave is bad, the lamps will light up half way instead of the whole length of the tube. If the MASTER is bad but the PWM circuits is still function and still send the PWM signals to the Slave, then the lamps will also light up but not at full length.
Right now the lamps did not even try to fire up for the error detection circuit to detect the fault, so you need to find out if you have BL-ON signal or not first, then if the PWM IC is getting the VCC to run.

[CraigR]

Re: Westinghouse Black screen W4207

I am getting 5volts at the connection you pointed out earlier for back light on.

[jetadm123]

Re: Westinghouse Black screen W4207

Sounds like it's getting the BL_ON command. Long shot, but try re-seating the wiring harness connectors on both inverters. Also, even though the fuses on both inverters check good, try checking the 4 mosfets on each inverter for shorts.

[CraigR]

Re: Westinghouse Black screen W4207

The mosfets checked ok already. I ordered the slave inverter first to try and will report back when it comes in.

[CraigR]

Re: Westinghouse Black screen W4207

Well got that board and installed and same thing so I guess I will get the master then.