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Philips 27PT543S (27" tube) -- no picture/sound
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flipz



Joined: 26 Sep 2006
Posts: 6

PostPosted: Tue Sep 26, 2006 3:10 am    Post subject: Philips 27PT543S (27" tube) -- no picture/sound Reply with quote

Hey all,
I have no knowledge in tv repair, however I do fix computers for a living so with a little bit of help I may be able to get this tv working. I actually got this tv for free, and have no knowledge of it's previous state. However when I plug it in and turn it on, the green light (power light) comes on, but the tv never turns on. I can't hear any noise and nothing happens. I googled the model number (27PT543S) and have found tons of complaints of people saying this tv starts to turn off on its own, and then never turns on again. I'm going to assume that's what happened to this tv.

I have it opened up and don't see any obvious problems. The one fuse I see is in tact. I don't see any blown capacitors or anything of the sort. I only found one thing on the web that may help me fix it. It was a post of someone describing the exact problem I had (the power light comes on but no picture or sound) and the response was

Quote:
It needs a capacitor replaced. The location number is 2455 which is a 47 microfarad at 25 volts, but should be replaced with a 47 microfarad at 35 volts.

Sometimes two transistors need to be replaced if they got too hot, but this is rarely needed.

Also on these I always hardwire two traces that are destined to open that transmit data information from the tuner to the microprocessor.


Unfortunatly that's the only detail the person provided. The post is a couple of years old and there is no way to contact him. So can anyone provide me information on which capacitor is # 2455? And what does he mean when he says he hardwires two traces to open ..... to the microprocessor?

Any help would be greatly appreciated. I'm sure I could probably take this to a technician and get it fixed for about $150 (from what I've read online) but I could buy a brand new one for not much more. Thanks!

-Brent

Edit: Just looking around the board I've been able to find 2450, 2462, 2465, etc etc. No luck seeing 2455 yet. So I guess a schematic would help. Smile

Edit 2: I don't know why I ever bother posting on forums because I always find stuff after I do. haha. I found 2455. Now... any ideas where I can get ONE 35v 47mF capacitor? Haha. Also, I am still definitely wondering what the two transistors might be, because he said sometimes there's two but didn't list which ones. And what he meant by the hardwire thing.
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flipz



Joined: 26 Sep 2006
Posts: 6

PostPosted: Tue Sep 26, 2006 8:33 am    Post subject: Reply with quote

Well I replacted that capacitor, but no luck getting it to turn on. I can hear the high pitch whine of the tv when I turn it on, and I don't think I could hear that at all before but maybe it's just quieter in the room now. But it definitely doesn't sound like it ever actually turns on. So I guess it's something else.

Any one have suggestions?
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PostPosted: Tue Sep 26, 2006 7:04 pm    Post subject: Reply with quote

Is it a constant high pitched whine like a working set? Do you have high voltage and can you feel static on the front of the screen? Can you measure the B+? If it is a loud whine it may be a short on one of the secondaries.
T.V.'s don't pull apart like computers, you may need some expensive test equipment and there are several areas with lethal voltages you need to be cautious of. Make sure you have learnt and understand these first.
Do you have the service manual? The schematic for it will be an invaluable resource to you. I am not sure if it is available on this site.
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flipz



Joined: 26 Sep 2006
Posts: 6

PostPosted: Wed Sep 27, 2006 12:15 am    Post subject: Reply with quote

Thanks for the reply!

I do no thave the schematic, and wasn't able to find it on this site. However by googling to numbers on the board I was able to find something. I'm not sure if it was what I needed though because I never downloaded it since I replaced the only thing I knew to replace.

It is a constant whine like a working set, but not as loud as my Philips 19", but that could simply be due to the age of my 19. I have to get kind of close to the 27" to hear the whine, but I definitely hear it as soon as I turn it on, and until I turn it off. There is no static on the screen, and aside from the light whine I never hear it actually turn on. The no static was the dead giveaway to me that it wasn't actually turning on.

I do know about the high voltage inside the tv. I don't know exactly where, but I have made sure to not put my hands on anything other than parts I know are safe. I haven't touch anything dealing with the picture tube or any of that stuff, because I know nothing about it. I'm smart enough to at least stay away from it. Smile

What would I need to do to measure the B+? I tried googling it, but just found a bunch of things saying to measure it. Nothing on what it is. I do have a multimeter to test with, as long as you are able to let me know what exactly I'm testing.

If it comes down to needing expensive equipment or what not I'll just give up. I just thought it would be a great way to upgrade my tv for little money.

Any help is still appreciated. Thanks!
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PostPosted: Thu Sep 28, 2006 7:46 pm    Post subject: Reply with quote

I wrote this yesterday but it said the server was unreachable when I went to submit it.
The B+ is the output from the chopper transformer which feeds the HOT and eventually the line transformer. If you are lucky there may be a B+ marking on the circuitboard and maybe even a post or PC pin to measure from. Make sure you measure from the correct ground, as there are several grounds in a set. (90 - 160Vdc) If it is lower than specified there may be a short on one of the secondaries. Do the heaters glow near the tube socket?
Measure the resistance collector to emitter of the HOT, if it is low both ways remove it and measure it again. (remember there are resistors and maybe a diode across the pins)
Hardwiring is wiring with hard wires. (soldered or screwed each end)Maybe there is a fault with the circuit tracks? T.V. circuitboards are nowhere near the quality of motherboards.
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Sat Sep 30, 2006 3:25 am    Post subject: Reply with quote

Check c2455 47uf 25v, q7462, q7463 and hot q7460 Bu4508Dx.
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PostPosted: Tue Oct 03, 2006 3:44 am    Post subject: Reply with quote

minnie wrote:
Check c2455 47uf 25v, q7462, q7463 and hot q7460 Bu4508Dx.


Thanks, this seems to be consistent with other info I have read. Unfortunatly I haven't been able to find a schematic for this chassis though (L01.1U AC07638) and I haven't had any luck finding anything other than 2455 which I already replaced.

Although I am also fairly illiterate when it comes to tv's and (considering it's my first fix attempt on one) I'm not sure what all your terms mean. What does the c in c2455 mean? And q in q7462? Also... HOT q7460?

Sorry for being dumb. I know I can figure this out, I just need to be pointed in the right direction. But I'm loving it because it's giving me something to do. Thanks!

-Brent
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flipz



Joined: 26 Sep 2006
Posts: 6

PostPosted: Tue Oct 03, 2006 4:07 am    Post subject: Reply with quote

Oops, forgot to login. That was me that posted above though.

Also:
Quote:
Do the heaters glow near the tube socket?
I don't see anything glowing when the TV is on, so I presume no. I need to learn more about all of this. The good thing is I love electronics, and love to learn!
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PostPosted: Tue Oct 03, 2006 6:35 pm    Post subject: Reply with quote

C = capacitor
Q = transistor
D = diode
R = resistor Some resistors are flameproof (fusible) These have to be changed with the same type otherwise you will create a fire hazard.
HOT = Horizontal Output Transistor
If your heaters glow, then the HOT is O.K. Measure The HOT for shorts, it is a really big transistor mounted on maybe the biggest heatsink near the line transformer. The line transformer is the one with the sparkplug lead coming out of the top, going to the suctioncup on the back of the screen. Beware of this transformer and this lead as there could be 30 000volts here with the set unplugged.
Maybe you could get the number off of the back of the set, ring the manufacturer and ask for the service manual? It may be worth $30 or so that is costs.
http://www repairfaq.org/sam/safety.htm
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flipz



Joined: 26 Sep 2006
Posts: 6

PostPosted: Wed Oct 04, 2006 3:51 am    Post subject: Reply with quote

Well I ended up finding the schematics and service manual for l01.1a which seems to be very very close (if not identical) to my l01.1u.

In it, it says that if you turn it on but get no picture or sound that feedback resistor 3523 may be defective. The part number is 482205210479 and it's a 47 ohm 5% 1/3w resistor. Unfortunatly the radioshacks around me only have 1/4w and 1/2w in 47 ohm so I guess I'll be buying it online and pay far more for shipping than the item costs.

It says to test if this is the cause that I should "Check power supply IC 7520. Result: voltage at pins 1, 3, 4, 5 and 6 are about 180 V and pin 8 is 0 V. The reason why the voltage on these pins is so high is because the output driver (pin 6) has an open load. That is why MOSFET 7521 is not able to switch."

I see where 7520 is on the board, and the 8 pins, but how am I testing them? I have my voltmeter, but what do I ground to? And should it be turned on while I test this?

Thanks as always,

-Brent
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