Flatscreen virgins grand opening
 

Decided to pop my cherry on a flatpannel tv given to me from work after it quit.

It was used to play safety DVDs once or twice a month, so I presume it has low mileage... Nothing invested in it at this point, but i figured ide give it a go- or give it a toss....

Basicly, i plug it in, push the power button, red LED lights an i hear a pop from the speakers as you normally would and.....THATS IT.... If i push the power button again, the LED will blink, ill hear a pop, and nothing else, It wont even load a DVD.. Same behavior if i use the remote on it....

Ive opened it and shot some pics... E-caps arent bulged and... thats as far as i know about these sets!! heheh :D

Please feel free to chime in if you have experience with this model and can get me started in the right direction

Thanks...
SR

Have you found any service info on ElectroTanya or the other manual/schematic sites?

I would start by looking for the power cabling between the power supply/backlight board and the Signal board and DVD player board. Often the proper voltage rails are marked on the connector. Typically you would have a 5VSB (standby-on all the time), +15, +5, and +3.3V, and perhaps a few others. See that they come up when power is applied. If not, look for shorted components on the affected rail, or an open/high ESR filter cap or a blown fuse.

Any links to the manual i need? electrotanya wasnt completely in english, had trouble navigating it.. Not seeing any volt listings on the boards.. :)

SR

You may find a schematic for the power supply board by looking up the part number. Looks like a MEGMET power supply used in a lot of off brand sets, so it will be something like MLT666. Seen them in sets sold under many different names here. I've seen an almost identical sets, but the ProScan brand isn't used here.

From the sets behaviour it sounds like the power supply is shutting down when the TV comes out of standby. The first thing I'd be looking for is shorted diodes, though that isn't the only possible fault. On these they're on the top right corner of the board near the connectors. The voltages should me marked near the connectors, possibly on the bottom side of the board.

ProScan was supposed to be the premium RCA product. :thumbsdn:
I got a headache just looking at the pictures. :sigh:
The thing consumes 130 watts. I thought those things were supposed to be energy efficient.

I'm far from an expert on flatscreens, but it appears that the power supply and video (Y sustain?) is combined into one board, the big one of the left of the middle photo. Check for shorted transistors and diodes. Find the part number on the board and you might be able to find a good used replacement on e - bay. I don't know if it's a plasma or LCD, but looking at the power consumption, that lead me to think it might be a plasma screen. Just googled the model number, It's not a plasma it's a LCD set.

Poked around online and found this pic of my supply (hope its okay to use)

Didnt see the voltage markings till now.. :)

The pic my gal shot of this board was so blurry,(pain pill) i had to look around for a match and i do believe this is the one.... Definitely a match side by side..


SR

You can make a request on http://www.freeservicemanuals.net .The guys might have a manual there for free for you.You got to join for free to do so..

Power supply with the inverter for the ccfl lamps. Y sustains are in plasmas only. shine a bright light on the screen while pushing the menu button and see if there's anything there. check for shorted mosfets or fet's. check continuity on the inverter transformers or a blown micro fuse

Even sadder? This tv spent its life (7 yrs) being carried from an office--- plugged in---- Ran for 15 minutes showing a DVD --Unplugged---Returned to the office---ONCE A MONTH... Talk about LOW HOURS.. :no:

I wonder if the plug in/out--in/out didnt surge the Power supply? And if i do find a defective part on this board can those teeny-tiny parts be replaced?? I see some micro tools in my future..

SR

Took some voltage readings: 5v standby is present, hooked up to the 12v tap and tried a power up, voltage jumps up then drops, so its safe to assume the power supply is trying to come up but shuts back down. So dr.ido's guess is looking valid..

Ebay sells repair kits for this board, most seem to focus on the 2 caps near the connectors.. Are the mfd ratings that critical for these boards? I may have some good ones from some salvaged receivers exept the voltage ratings may be higher I dont have the ESR meter to check the current ones, may need to do some cap swapping since a no bulge cap can still be bad... Any ideas?

Your input is most appreciated..

SR

The caps are not that critical in these (there are some exceptions, but not for this board). As long as the voltage rating is at least as high as the original and the capacitance is somewhere near (eg, replacing a 2200uf with 3300uf or vice-versa) it will work. Near the 2 caps near the connectors the zener diode and the to-220 package diode often short in these.

That said, if the 12V rail is coming up at all the short isn't on the 12V rail.

In your set there is a small DC-DC sub-board mounted between the power supply and the tcon board. These can and do fail shorted. If it has failed it could shut down the power supply board, disconnect it and see if anything changes.

If you are referring to the small board with the round copper transformer, i unplugged it and it changed nothing except the speakers werent popping anymore. can the diodes be tested in circuit? if yes, i may have a shorted glass diode near the to-220 near the connectors.. (it read near zero both ways)..

SR

Diodes can USUALLY be tested in circuit, but not always. One that reads zero in both directions is definitely suspicious. Lift one end and recheck before replacing it though.

Biggest problem I have had with these is the backlight boards. Look for discoloration under the transformers on the backlight board. This is a sign the transformers were overheating/failing and that shorts the driver transistors. I would check all the driver transistors for shorts on the backlight board. If one is bad, I have never been lucky to replace the transformer and transistor. I would replace the board if any shorts are evident.

Those inverter transformers operate at high voltages, and they are prone to insulation breakdown and shorted turns, which then overheat and blow the driver FETs. By the time you source the parts (if you can get them) and install them, you might be best off looking for a used board on eBay.

A backlight fault on these doesn't shut the power supply down. The set would power up normally with no backlight. The glass diode is a Zener and often shorts on these, from memory it's 5.1V. It will shut down the power supply if it has failed. If it has shorted also replace the 2 10V 1000uF caps (unless they test good with an ESR meter).

Those are the 2 caps i was talking about replacing, i was thinking of replacing them with 16v ones.. Im uncertain about the zener being shorted, i hook it one way, and the digits begin to climb as if ive hit a capacitor in the circuit. my meter isnt zeroing out when i test it. The numbers are low but not zero... I'll have to test it again to be sure.. Ide hope the backlights are okay, this set has less than 30 hrs on it as stated earlier :D

SR

It is fine to replace the 10V caps with 16V caps. The zener diode will read close to 0 in both directions if it is shorted. Otherwise it will read around 0.7V (using the diode check range on a digital meter) in one direction and open in the other. In circuit other components around it can effect the reading. If you're unsure unsolder one side of it and test again.

Unsoldered a pin on the zener and its not reading a short, The to-220 tests fine on diode position...

SR

Went as far as running without the zener and no change. The to-220 tests fine on the diode setting on my meter so its back in circuit. Double checked my voltages and all the + and- 5 volts are present. The 12v pin only gets as high as 3v before it falls due to the instant shut down.. Swapped the 1000uf@10v e-caps with an exact set of used ones. I dont have an ESR meter, I am using a centech #69096 digital meter if that helps reference my tester and its functions...

The dc-dc sub board mentioned gets to 14v before the shutdown...

any other culprits on this board i need to check??

SR

I don't have one in front of me right now to check, nothing immediately obvious jumps to mind. Have you tested with the 12V line disconnected from the main board to rule out a fault on the main board dragging to down? I've seen this when the audio amp IC fails.

Mainboard is fused and they check OK, however, i did remove the 12v lines to all and the result was the same. Its definitely within this board somewhere.. I dont know if the 12v rail is okay, it never reaches 12v before shutdown, but i gained 2 volts without a load, meter reaches to 6v before cutoff... Definite head scratcher this one be... :)

SR

There's a Zener on the 12V rail hiding between a couple of caps under a blob of silicon on the one that I have on the bench. There's a FET on the bottom of the board but I don't think it's on the 12V rail. I've tried tracing these out further in the past and hit a dead end with the unmarked (or unreadable) SMD parts on the bottom on of the board. At that point you're already into it for more than a 26" LCD TV is worth.

If I get time I'll have another look at the one I have here, I don't remember what was wrong with it.

No worries... It was a freebie and my first look inside one of these flat screens. Definitely a great learning experience and i appreciate you folks walking me through it. I can see why there are no more tv shops in my town...

Been looking on ebay for the local board offerings and searching for a cheap one, first im gonna exhaust myself on this one before then. Ill check that zener next and do some more poking around..

Thanks.. :)

SR

Upside??? i did get a board of Ebay...... Downside? My board is in better shape, The replacement i ordered has NO output voltages at all (yes, i confirmed voltage going into it ) :D

Since i dont have an ESR, i think ill make a trip to the store and go FRESH caps for the old board and see what happens..

SR

How about a cheapie bare board model?

https://www.amazon.com/Yosoo-Display...W7SKV0QNA8K8G9

not affiliated,
jr

You can get them for half that on the-bay...

Replaced the 1000uf-10v with 35v ones and still wont come out of standby. Still beats the DOA board i got off ebay :D

Back to the ole drawing board.......

SR

Got another board and STILL wont come out of standby.... Any way to kick the power supply on without hooking the tv works up to it? Also i noticed a green led on the power board, in what situation will this light??

SR

There is a PSON pin that turns the main power supply when it changes state. If it is 0V in standby connect it to the 5V standby rail via a 100 ohm or so resistor. If it is 5V in standby connect it to ground via the resistor.

From memory the PSON pin for these boards is on the larger connector next to the 5V standby pin and it goes to 5V when the set is on, but I don't have the board in front of me to check.

mine has (+12v--GND--+5v--+VS--SB--+5v--GND) taps...

Have you ever seen the LED lit on this board? Just wondering if it comes on during power on?

SR

+VS is probably the 5V standby rail and SB is PSON. I don't remember the LED and I don't have one on hand at the moment.

Okay, ill give it a go... :)..... Will a 150 ohm work?

SR

Perhaps it's time to dump that "virgin" into a volcano and be done with it.:D

LOL!!! Damn close to it..... :D

SR

The resistor value isn't critical. I've just shorted the pins when I've been lazy, but it's safest to use a resistor.

I did use the 150k and..... it started making power.... Ive got 11.?? coming off the 12v tap.. i plugged the small DC-DC board you mentioned earlier and its outputting 22v.. All is hooked back up except the plug that i have the resistor set on. The LCD backlights are not on. Beginning to believe the fault is elsewhere...

SR

Still messing with this set... Mostly out of boredom, SMOKE or SCREEN will be the outcome...

With the SB jumped, and the board making power, should i be expecting to see the back light bulbs on since theyre hooked to the mip-260 board? Or are they triggered on by another source?

SR

proscan
 

We used to sell these things. Actually, we still do as an RCA branded item. The main issue with these when we used them in store was the DVD player shorting out and killing one of the boards, and on one occasion letting the smoke out on the sales floor. If you really want to fix this dog, Sears still sells all of the boards. I think that they are the only licensed parts/repair center for RCA in the country.