Electronic equipment repair and service manual search discussion :: Topic review - Philips 27PT543S (27" tube) -- no picture/sound

Gizzard · Posted: Sat Aug 02, 2008 6:55 pm Post subject: Q7460/philips tv

Does anyone know the specs on Q7460? I de-soldered it from the pcb and then it went flying.....

twagz · Posted: Thu Oct 05, 2006 10:23 am Post subject:

Try replacing C2455...it is off pin 3 of the flyback. The transistors that usually go bad are Q7460 which is the H.O.T., and also Q7461, Q7462, and Q7463. You can check the transistors easily if you have a diode check on your multimeter...

flipz · Posted: Wed Oct 04, 2006 4:29 am Post subject:

Ok, I was just able to enter SDAM and get error codes off of the blinking LED. This is what it apparently indicated:

10 4 5 6 2

10: Tuner, Tuner I2C identification error. 1000, 7482
4: MSP34X5/TDA9853, MAP I2C identification error. 7831
5: TDA95XX, POR 3.3V / 8V Protection. 7200, 7560, 7480
6: I2C bus, General I2C bus error. 7200, 3624, 3625
2: n/a, Horizontal protection. 7460, 7461, 7462, 7463, 6467

Hrmm.... that's a lot of problems. Confused

flipz · Posted: Wed Oct 04, 2006 3:51 am Post subject:

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

Guest · Posted: Tue Oct 03, 2006 6:35 pm Post subject:

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

flipz · Posted: Tue Oct 03, 2006 4:07 am Post subject:

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

Also:

Guest · Posted: Tue Oct 03, 2006 3:44 am Post subject:

minnie · Posted: Sat Sep 30, 2006 3:25 am Post subject:

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

Guest · Posted: Thu Sep 28, 2006 7:46 pm Post subject:

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.

flipz · Posted: Wed Sep 27, 2006 12:15 am Post subject:

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!