philips 170s turns on for 1s and than dead

[Audison]

Re: philips 170s turns on for 1s and than dead

Case closed on this monitor. The panel would work fine but we made a mistake when disassembling the panel and that is the reason why there is only half of the screen picture.
I might buy the broken part when I get a chance to get this panel working once again but for now it's going into storage.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

Um. Is it too late for me to pitch my problem in this same thread?
Exactly the same problem here. I replaced all bulged caps, but still no go on the 2 sec to black. Also tested transformers, seem to be working, I guess. I can't find the fault. Help, pls?

[budm]

Re: philips 170s turns on for 1s and than dead

Um. Is it too late for me to pitch my problem in this same thread?
Exactly the same problem here. I replaced all bulged caps, but still no go on the 2 sec to black. Also tested transformers, seem to be working, I guess. I can't find the fault. Help, pls?

Did you verify that the lamps are good or not?
Verify the board: https://www.badcaps.net/forum/showth...er+testing+cfl

[mihovilko]

Re: philips 170s turns on for 1s and than dead

I'll try to do that in the near future.
Is it possible to connect original lamps one at a time and power them through the circuit to see if they're ok? Or do they all need to be working at the same time?

[budm]

Re: philips 170s turns on for 1s and than dead

You can test one lamp at a time and see each one will light up or not. The lamp will not stay on of course because the protection will kick in, it only take one bad lamp for the protection to kick in.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

Yup, all the lamps flash on. Any other suggestion?

[Stevedb]

Re: philips 170s turns on for 1s and than dead

The problem of the half screen are the little flex cables.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

Well, it's not a half screen problem, it's 2 seconds to black.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

OK, so if it's not fixabl, could someone pls tell me which part of the board to disconnect so I can at least use the 12V and 5V outputs as lab power supply?

[will62]

Re: philips 170s turns on for 1s and than dead

Can you read the part numbers circled in the pic?

[mihovilko]

Re: philips 170s turns on for 1s and than dead

7808 is: bjt31936 f18k8 06535
7823 is: 40T03gh 534546
7806 is: 4415GH 536418

[will62]

Re: philips 170s turns on for 1s and than dead

OK, I think that I've found the information:

7808 = BIT3193G driver IC
7822 = P-Channel mosfet
7823 = N-Channel mosfet

1. Check both mosfets for shorts. (short middle pin is same as top tab)
2. Check the 2 diodes on opposite side of board (between transformers)
3. When you say that you checked the transformers, I'm assuming that you
made sure that the secondary windings on the 2 transformers above mosfets
were not open and pretty close to each other in resistance, correct?

After checking these items, we will need an LED to bypass the driver IC's
shutdown. Do you happen to have one?

[mihovilko]

Re: philips 170s turns on for 1s and than dead

Progress!

the P channel mosfet shows 0.171 V voltage between D and S,
and I can read that same voltage on both the diodes on the opposite side (using diode check function).
So the diodes seem to be shorted, altough the meter doesn't chirp in continuity mode.
On the second mosfet (N channel) I read 0.180 V from S to D.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

Vis a vis the transformers:



and again, the continuity doesn't sound off on either.

[budm]

Re: philips 170s turns on for 1s and than dead

Progress!

the P channel mosfet shows 0.171 V voltage between D and S,
and I can read that same voltage on both the diodes on the opposite side (using diode check function).
So the diodes seem to be shorted, altough the meter doesn't chirp in continuity mode.
On the second mosfet (N channel) I read 0.180 V from S to D.

Are you getting the reading on both direction of both MOSFET's S & D pins?
The MOSFET has body diode between S and D pins so it should show the reading like diode between S and D.

[will62]

Re: philips 170s turns on for 1s and than dead

Any suspect component would have to be taken out of circuit and rechecked.
I'm a little concerned about your measurements for the secondaries of the transformers:

left : 500 ohms
right : 300k ohms

The one on the right in the pic is awfully high. I'm wondering if it's actually open, and you're reading 300k ohms from something else in circuit. You may want to remove it from the circuit, or possibly remove the solder on the secondary pins, so they are isolated from the circuit.

Edit: posted before reading Budm's post. Budm, what do you think about the secondary resistances?

[budm]

Re: philips 170s turns on for 1s and than dead

I would remove the one that shows 300K, or maybe his probes did not make good contact with the solder pads.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

I checked for reverse continuity on the mosfets and I get a reading in only one direction.
As for the transformer, I rechecked it and it really is 300K. I'll disconnect it and measure again.

[mihovilko]

Re: philips 170s turns on for 1s and than dead

Yup, still the same. 0.355 MOhm reading.

[budm]

Re: philips 170s turns on for 1s and than dead

Can we see the bottom side of the transformer to see how the windings of the transformer are connected to the pins?