Westinghouse 55" - mostly dead

[art_dodger]

I have a cheap junky Westinghouse WD55UW4620 TV in my shop. (Pretty sure these are Wal Mart/Best Buy specials...)

Problem: Won't power on. Red power LED on constantly, power button/remote does nothing. No variation/indication when pressing power button.

All boards look good, no popped caps, nothing looks burnt.

Checked all power board voltages (between power brd & main brd) - All appear to be within reasonable values as per the board markings. Nothing missing, nothing too far out of whack. No voltage changes anywhere when pressing power button.

I suspect the main board (only because all the power board voltages seem right...) - Disconnecting power board connector Con2 that is connected to connector J6 on the main board does NOT turn on backlights like most LCDs I've repaired but I can't locate a service manual for this model so I'm not sure if it's supposed to on this model.

SO far I've tracked down a replacement main board from one of my regular sources for around $120.00. Before I spend money for nothing...

Anyone have any good tips on confirming a little more clearly whether it's more likely to be a problem with the main or the pwr board? I have all the necessary test equipment, including a scope but without a service manual/schematic the test equipment is kinda useless.

TV: Westinghouse WD55UW4620
Main board is a CV6488H-A-20.
Power board is aAY155D-45F12

I'm an experienced tech - Any tips/advice (or a link to the service manual) would be gratefully accepted.

[dick_barton]

Re: Westinghouse 55" - mostly dead

As you say without the circuit diagram there's no guarantee that the backlights come on. What voltage is on Backlight_On Pin on the power board and have you tried jumping standby voltage to it via a 1K resistor. Do all the supplies come up when the mainboard is disconnected or maybe you also have to jump STB voltage to Power_On via a second 1K.

[art_dodger]

Re: Westinghouse 55" - mostly dead

As you say without the circuit diagram there's no guarantee that the backlights come on. What voltage is on Backlight_On Pin on the power board and have you tried jumping standby voltage to it via a 1K resistor. Do all the supplies come up when the mainboard is disconnected or maybe you also have to jump STB voltage to Power_On via a second 1K.

Thanks for the reply (sorry for the delay in responding) - Unfortunately without a schematic, I can't even identify the BL_ON pin - The connectors have voltages listed but there isn't much to identify the purpose/source of each pin.

If anyone has a link to a schematic/service manual for this thing, it would be appreciated. Thanks!

[dskall]

Re: Westinghouse 55" - mostly dead

Need to check if you are getting voltage to buttons/ir and voltage changes with key presses.

[budm]

Re: Westinghouse 55" - mostly dead

We NEED good clear pictures of the board, especially the power supply board.
Are you sure that 'aAY155D-45F12' is P/N of the power supply board?

[art_dodger]

Re: Westinghouse 55" - mostly dead

We NEED good clear pictures of the board, especially the power supply board.
Are you sure that 'aAY155D-45F12' is P/N of the power supply board?

As requested. (Thanks)

IMG_2033 - Main Board
IMG_2029 - Power Board
IMG_2031 - Power board sticker

[art_dodger]

Re: Westinghouse 55" - mostly dead

Just looking a little closer, the power board part number is AY155D-4SF12, not AY155D-45F12 as I'd originally listed. (The 5 and S look too similar for these old eyes I guess) :-)

[dskall]

Re: Westinghouse 55" - mostly dead

Your board seems to be marked. Are there markings on con4 under the silicon? You got your voltages when you forced power supply on? Are your button voltages changing when you push them?

[dick_barton]

Re: Westinghouse 55" - mostly dead

The voltages are given in the boxes alongside the connectors
What voltage is on PS/ON and 5VSB

[art_dodger]

Re: Westinghouse 55" - mostly dead

Your board seems to be marked. Are there markings on con4 under the silicon? You got your voltages when you forced power supply on? Are your button voltages changing when you push them?

From my OP: "Checked all power board voltages (between power brd & main brd) - All appear to be within reasonable values as per the board markings. Nothing missing, nothing too far out of whack. No voltage changes anywhere when pressing power button."

[art_dodger]

Re: Westinghouse 55" - mostly dead

The voltages are given in the boxes alongside the connectors
What voltage is on PS/ON and 5VSB

From my OP: "Checked all power board voltages (between power brd & main brd) - All appear to be within reasonable values as per the board markings. Nothing missing, nothing too far out of whack. No voltage changes anywhere when pressing power button."

PS_On sits at 4.72vdc, no changes pressing pwr button, no changes with IR power button... All voltages marked on power board appear to be witin .2v of what's marked on the board.

[vinceroger69]

Re: Westinghouse 55" - mostly dead

certainly sounds like a mainboard issue as you have now checked the voltages are ok

[art_dodger]

Re: Westinghouse 55" - mostly dead

certainly sounds like a mainboard issue as you have now checked the voltages are ok

Yeah that's kinda the direction I'm leaning as well... I'm not seeing anything hinky that makes me suspect the power board, so it should be the main... I figured I'd check with the experts here to maybe educate me with some additional tips on flipping the coin as to whether it was more likely a Main or Power Board replacement.

I'm usually lucky enough to have some sort of reasonable "evidence" that narrows down the suspect but in this case, particularly without a schematic/service manual, I'm not sure. (I just got burned for 2 mainboards I replaced where it turned out to be the power boards after all... Ah well, I'll add them to my "spares" but that gets expensive quickly...)

[dskall]

Re: Westinghouse 55" - mostly dead

So you forced your power supply on to get your voltages? You checked your button connector at your mainboard and got voltage changes on button presses?

[budm]

Re: Westinghouse 55" - mostly dead

http://www.shopjimmy.com/westinghous...er-supply.htm#
Westinghouse AY155D-4SF12 Power Supply
Pictures provided by SHOPJIMMY.
BL-ON is on the 3-PIN connector with BL-ON, ADJ, and GND labels next to it.
See what you have on BL-ON pin.

[art_dodger]

Re: Westinghouse 55" - mostly dead

http://www.shopjimmy.com/westinghous...er-supply.htm#
Westinghouse AY155D-4SF12 Power Supply
Pictures provided by SHOPJIMMY.
BL-ON is on the 3-PIN connector with BL-ON, ADJ, and GND labels next to it.
See what you have on BL-ON pin.

Ahhhh, THAT's where it is.... The labels are covered with a big gob of potting compound so I couldn't see it initially. Thank you!

So - BL-ON: .05vdc. Disconnect cable between Main & Power board, BL-ON jumps to 1.34vdc then slowly decreases to close to 0 over 2-3 seconds. Doesn't matter if backlights are connected or not, same voltage readings.

2-wire back light connectors (wired to backlights) on pwr brd: .65vdc, decreases to 0 when pwr brd <-> main brd ribbon disconnected.

PS/ON: 4.71vdc, Does NOT change when pressing power button.

Thanks so much for the assistance so far guys...

[art_dodger]

Re: Westinghouse 55" - mostly dead

So you forced your power supply on to get your voltages? You checked your button connector at your mainboard and got voltage changes on button presses?

NO, I didn't have to jumper or force the PS - Correct voltages are all present the moment I plug in, without having to command the set on. (Seemed unusual to me too...)

The power button itself and cabling seem fine - Although I can't identify which pins on the main board connector are specifically tied to the power button, I CAN see resistance changes when pressing the button & measuring each pin (there's an 8-wire ribbon cable from the button module to the main board - I measured each pin) to ground. They ALL show some change in resistance when the power button is pressed.

Any further tips or suggestions gratefully accepted. :-)

[art_dodger]

Re: Westinghouse 55" - mostly dead

Bump - Any further suggestions from anyone re: narrowing down between Main Board and Power Board?

[dskall]

Re: Westinghouse 55" - mostly dead

What is your ps-on voltage with connector disconnected? Could be an eeprom problem since it won't respond to keys. You could try a reset on it.

[dick_barton]

Re: Westinghouse 55" - mostly dead

So with the mainboard disconnected you have all the following voltages on the power supply.
+5VSTB, +5V, +12V, +24V
PS/ON is 4.7V and does not change and BL/ON is 0.5V

If you jumper +5VSTB using a 1K resistor to BL/ON does that bring up the backlights.