Westinghouse WD40FW2490 not powering up

[Mr_Slim]

Hi All,
this is a Curbside special, so I'd really like to troubleshoot the issue before breaking down and replacing the main board.

It has an ST6308RTU-AP1 main board, like Seiki, and others, with I assume specific firmware for this particular model of Westinghouse TV. This is an all in one board with both power supply and logic on it.

Here's what I've done so far:
Tried some of the Reset sequences found on other sites, with no success.

Checked for the 5 volt standby voltage as per Bud's troubleshooting doc, not found on the connector pins, so I think this is the best place to start.

Has anyone found a schematic for this board?

Any other suggestions appreciated.

[budm]

Re: Westinghouse WD40FW2490 not powering up

If you upload good clear pictures of the boards and how they are all connected together that will be a good start.

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

Thanks, here's a big picture view of the connections, and a couple of closer ones, flash and no flash.

[Andrew F. Ali]

Re: Westinghouse WD40FW2490 not powering up

This is one of those Chinese universal boards. So you will not find any service information per say. These boards are used in other TVs and can different software are used for different Panels. Since you have no Standby voltage that would be the place to start. Are you getting 125Vac in? What voltage are you getting across the big filter cap and are the fuses OK?

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

I'm getting 120Vac in, yes. And the fuses appear to be ok. The voltage across the big filter cap is 165V DC..
I found two connectors at 4:00 from the yellow transformer, that have 5VS,12VS and ground on them. 5VS is zero, and the 12VS measures around 3V..

[Andrew F. Ali]

Re: Westinghouse WD40FW2490 not powering up

Test the HOT/Primary side components for any faults. I believe this is an always ON type PSU. We would need to see pics of the board's underside, also.

[budm]

Re: Westinghouse WD40FW2490 not powering up

https://www.badcaps.net/forum/attach...4&d=1528206069
Waht DCV do you have at the Cathode of D2014, and at D2012's big metal tab with ref. to the chassis GND?

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

OK.. The Cathode of D2014 is 0V DC with ref to Chassis Ground.
The tab on D2012 starts at ~3.15 V DC and then starts going down, like a capacitor is being drained..

[budm]

Re: Westinghouse WD40FW2490 not powering up

OK, check the RESISTANCE of those diodes in both directions, report the resistance readings.

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

D2014 and D2011 (beside it) appear to be shorted (0 ohms in both directions).

D2012 is shorted between the two small pins on top, and connection from each pin to the big tab appears to charge and discharge via the circuit around it depending on the polarity of the meter leads.

[budm]

Re: Westinghouse WD40FW2490 not powering up

D2014 and D2011 (beside it) appear to be shorted (0 ohms in both directions).

D2012 is shorted between the two small pins on top, and connection from each pin to the big tab appears to charge and discharge via the circuit around it depending on the polarity of the meter leads.

D2014 and D2011; Remove them and tested them off the board.

D2012 two small pins are joined together so the reading is correct, it looks OK.

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

Both 2014 and 2011 measure about 900K in a positive direction (+ on the Anode and - on the Cathode) and open in the opposite direction. They are MUR460 diodes.

[budm]

Re: Westinghouse WD40FW2490 not powering up

Both 2014 and 2011 measure about 900K in a positive direction (+ on the Anode and - on the Cathode) and open in the opposite direction. They are MUR460 diodes.

Measure the empty pads where those two diode are to see if it still show as shorts as reported when measured with the diodes in place. The shorts may be on the board itself since the diodes did not show as shorted off the board.

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

Yep, the pads show a short.

[budm]

Re: Westinghouse WD40FW2490 not powering up

Yep, the pads show a short.

So the resistance between the Anode pad and the Cathode pad shows as shorted, remove that small blue disk cap sitting between those two diodes to see if the short will go away or not, that snubber cap is connected in parallel with those two diodes.

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

After pulling the snubber cap, the resistance across the diode pads is about 1.7 ohms.
The cap itself seems to charge/discharge on the Megohm setting on the meter, and does not show as a short on any setting. There are 3 x 150 ohm resistors in parallel underneath the diodes that measure ~50 ohms, so that seems right also.

[budm]

Re: Westinghouse WD40FW2490 not powering up

I have a feeling there is shorts circuit on the Cathode side of the Diode, you can verify that by checking the resistance between GND and the Cathode pad.

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

So, cathode to ground on both diodes shows about 1.5 ohms, while Anode to ground is .1 ohm, which is the same as the resistance of the meter leads, so effectively a short..

[R_J]

Re: Westinghouse WD40FW2490 not powering up

If the diodes are out, what you are measuring on the anode side is the transformer winding which will be .1 -1 Ω. you have something shorted on the cathode side somewhere. Check the transistor Q2054

[Mr_Slim]

Re: Westinghouse WD40FW2490 not powering up

OK, so the right pin (source) to the tab is .8 ohms. and the left pin (gate) to the tab is 384 ohms. (both directions). I presume the Drain (middle pin) is tied to the Tab?