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Hello, I have an RCA P46729BA big screen projection. Chassis # PTK169PCA and serial XXXXXXXXX I've had it since '94, the power supply has died twice in it and it's out again. The guy I've had fix it in the past is no longer around and no one else wants to even look at it because of it's age. (No surprise, but I don't have $1500 for a new TV). I am familiar with repairing computers, i.e. removing and replacing hard parts internally. Can I buy the power supply for this and swap it out? I know the dangers of static and that there is a lot of voltage hiding in TVs, but I am confident I can do it even if it requires some soldering. Is the power supply available from anyone or can I fix this one? All I see inside this thing is a chassis with a lot of different boards and components and nothing labeled 'powere supply'. I'm not sure where it is on this thing. Thanks for your time - Gary

Submitted: 26 days and 16 hours ago.
Category: TV
Value: $17
Status: AWAITING CUSTOMER ACTION
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Optional Information

Make: RCA
Model: P46729BA

Already Tried:
Chassis PTK169PCA, serial XXXXXXXXX Tried different outlets, Has had power supply replaced twice over its 15 year life. All other items work in outlet.

Accepted Answer

You will probaby fine out that your Horitzonal transistor is shorted, that is a real common problem on that model, and you can use a 2SD1885 for the output. And after you fix the output, you mifgt have a blown fuse, that blew after the transistor shorted. That is the reason you TV is in shutdown mode. The Hritzontal transistor is located on the high voltage power supply. It is the one with the fly back transformer on it. and The transistor is the one that is on a metal heat sink by the transformer. on the left side form the back. And where the AC cord plug's in at there a white plastic right behind it with a small fuse and the transformer is to the left. And behind the transformer there is a metal heat sink with a shorted out put, and that is the most common thing that happens to that Chassis. () % of the time that is the only problem and the part is less then 10.00. I'm working on the same chassis right now. The part is less the $10.00. Good luck.

 



Edited by Joe on 10/30/2009 at 3:39 AM

Expert: Joe
Pos. Feedback: 90.0 %
Accepts: 
Answered: 10/30/2009

Electr&onic Tech

Over 30 years in electronics, Board Repair, TV's, Gaming,

23 days and 21 hours ago.

Reply

Thanks, things are hectic right now. When I get a chance in the next few days, I will tear into it and try the recomendations you gave. Thanks for your answer. If I have questions or issues, do I communicate with you through this? Thanks - XXXXX@XXXXXX.XXX Gary

Posted by Joe 23 days and 21 hours ago.

Answer

I understand the model like the back of my hand, working on one right now, take care.

23 days and 21 hours ago.

Reply

Thanks a lot. As soon as this halloween thing is over and I get a chance, Tuesday I hope, I'll pull the chassis out and tear into it.

Posted by Joe 23 days and 20 hours ago.

Answer

I leaving for halloween thing too.

22 days and 21 hours ago.

Reply

OK, I have found the transistor you're talking about. I "looks" ok in the sense it's not burned or blown apart like I have seen in the past with other electronic items I've worked on. The fuse checks out fine also. Is there a way to test this transistor while mounted to the board? The board has obviously been replaced due to the fact that 3 of the 4 mounting posts are not plugged into there sockets and the fat red wire from te transformer on the said board looks newer and is spliced with heat shrink tube to the black wire going to the transformer next to the cord socket. Do I need to be concerned about stored high voltage? Can I disapate easily? How do I go about testing things? Or do I just chuck it? lol I have piks if that would help. XXXXXXXXXX XX XXXXXXXXX XXX XXX

22 days and 20 hours ago.

Reply

I probed most all transistors and resistors on the board (power supply board?) along with all wires (except the white wires and black wires in the black connector on the top right of the board), all of them are at roughly 54V AC (+/- less than 1V) including all 3 legs of the transistors. 120V AC is going through the cord outlet to the 4 diodes on the main board. I also have 53V at the red wire coming from the main left board-going to a grey socket on the board to the right (as seen from the back). I visually inpected all transistors, caps, diodes, resistors and other comonets on the left bottom main board along with what I am assuming is the power supply board with the suspect transistor and didn't find anything burned, popped or bloated. I am unsure where to go from here. The last time it died like this, the repair guy replaced a resistor that connects the green side to the white side on the bottom main left board along with the "power supply". I have 53V there too on both sides of it. This resistor is behind a cap that is behind the height pot and has color bands "fat" gold, skinny pink & violet & red. It is to the left of the big white transformer. Trash?

22 days and 19 hours ago.

Reply

After a little more probing, I was wrong about the 4 diodes by the cord socket. 2 of them - CR1 & CR2 have 120V on one side and 55V on the other. The other 2 - CR3 & CR4 have 55V on one side and .9V on the other. Even the balck wire on the metal plate around the cord socket has 53V. I am using a Fluke digital volt/ohm meter with it grounded to a household ground wire. I tried using the metal plate at the cord socket and I only get 68V at the fuse that way so I assume the metal plate is not a ground or neutral.

Posted by Joe 22 days and 14 hours ago.

Answer

To check the horotzontal, Put your meter od Diode check and check to see if you get at least .4 reading across any two leggs on the transistor, with the TV off and unpulg. If you don't then it needs replaced. Tv will not start up if that is bad.

21 days and 18 hours ago.

Reply

I got .7 B to C, .6 B to E and .5 E to C. I checked the other 2 also, the one next to the horizontal reads the same and the one at the bottom read .6, .5 and 1.9.

Edited by XXXXXXXXXXX on 11/3/2009 at 2:48 AM

Posted by Joe 21 days and 14 hours ago.

Answer

There is a Big diode ac cap right by the horizontal, you will need to change them even if they read good, expecialy the cap. It also sounds like you might have a bad fly back .. I believe MCM electronics caries that fly back. That's about all that happens to that chassis, and it usually the horizontal.Also look around to make sure you don't see any fried resistors, And check under the board for hot spots. The other thing I just thought of is the high Voltage splitter goes bad too. and That is about everything that goes on that chassis. Check where the anode lead goes into the splitter and it might show signs of burning. You looking at a fly back, and a splitter. You should be able to get both under 100, and that is what I would do.

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