GNR TS902W no power , help please

[lcdcaps1]

Re: GNR TS902W no power , help please

Ok so I have just checked all the components as advised
To me all looks within spec
Below are my findings

All diodes have been checked for shorts and non found

F101, continuity beeps
000.8 ohms

D109,
0.532V
Black probe on band


D108,
0.539V
Black probe on band

D106,
0.546V
Black probe on band


D107,
0.539V
Black probe on band


D105,
0.113V
Black probe on band


D102,
0.179V
Black probe on band


D101,
0.168V
Black probe on band


c103,
099.3 K ohm

R129,
566.9 K ohm

R129,
565.1 K ohm

R130,
568.6 K ohm

R126-1,
000.8 ohm
R126-2,
000.9 ohm
R126-3,
000.9 ohm


R124,
3.751 K ohm

D103,
0.552V

R103,
003.1 ohm

D104,
0,454V


R109,
047.7 ohm

R124,
3.727 K ohm

R116,
1.004 K ohm

C111,
1.0006 K ohm

R115,
000.4 ohm

C109,
19 K ohm

Zd102,
0.719v

R125,
1.008 K ohm

Q103
0.63v, diode mode as instructed

J101,
000.8 ohm
J102,
000.7 ohm

C101,
10.14 M ohm

Zd103,
0.728 V

R127,
419.8 ohm

Hi

Thanks again for the reply
The SG6841 chip i had purchased brand new so had them on hand
I tested all the nearby components as mentioned here and all tested ok.
Tested resistors in resistance mode and diodes in diode mode.

As it is confusing all of you it is to me as well

I will go through and test all again and update thread

[momaka]

Re: GNR TS902W no power , help please

D102,
0.179V
Black probe on band


D101,
0.168V
Black probe on band

D101 and D102 have suspect low readings. Remove them from the circuit and re-test in *both* directions. That is, test when you have black probe on diode band side (cathode) and then reverse the probes to have red probe on diode band side. Post both readings for each diode.

D105 also has suspect low readings, but it looks like it's in parallel with a 47 Ohm resistor, so that's why it might be reading this low. Still wouldn't hurt to take it out of the circuit and check it just in case.

Q103
0.63v, diode mode as instructed

There should be 3 readings for Q103, actually:
- One between Base and Emitter (with black probe on Emitter)
- One between Base and Collector (with black probe on Collector)
- One reading between Collector and Emitter (here, it doesn't matter if black probe is on Emitter or Collector, but just for consistency, have the black probe on Emitter.)

Everything else looks okay, indeed. Just follow up with these results, and after that we will move to testing other parts of the PSU. I suspect either D101 and/or D102 are shorted -OR- there is a short-circuit behind them... though as to why the controller doesn't have a pulsing voltage on Vdd (to indicate fault-restart operation), that's another thing to worry about.

Can i run this power supply board without this diode

No, never run a circuit with parts missing, unless you very well know what those parts do and know that the circuit will be okay without them. This rarely happens, because if the manufacturer didn't need to put that part there, they wouldn't - after all, having to put less parts also means lower production cost for them, so they would have left it out if it could be left out.

[lcdcaps1]

Re: GNR TS902W no power , help please

Hi All
So I took the diodes out.
D101, D102 and D105
All test ok in one direction,
Black probe on band and red on other end and nothing in other way
(red probe on band and black probe on other end)

Tested for shorts as well and no shorts
below are results of diodes, (black probe on band and red probe on other end)

D101
0.169V

D102
0.172V

D105
0.469V

Q103 readings below

between Base and Emitter (with black probe on Emitter)
0.635v
between Base and Collector (with black probe on Collector)
0.618v

between Collector and Emitter (black probe is on Emitter.)

no reading shown if black probe is on emitter and red probe is on collector

If i switch probes around,
red probe on emitter and black probe on collector, i get reading
0.575v

Please can someone tell me if these diodes are ok
thanks all

D101 and D102 have suspect low readings. Remove them from the circuit and re-test in *both* directions. That is, test when you have black probe on diode band side (cathode) and then reverse the probes to have red probe on diode band side. Post both readings for each diode.

D105 also has suspect low readings, but it looks like it's in parallel with a 47 Ohm resistor, so that's why it might be reading this low. Still wouldn't hurt to take it out of the circuit and check it just in case.


There should be 3 readings for Q103, actually:
- One between Base and Emitter (with black probe on Emitter)
- One between Base and Collector (with black probe on Collector)
- One reading between Collector and Emitter (here, it doesn't matter if black probe is on Emitter or Collector, but just for consistency, have the black probe on Emitter.)

Everything else looks okay, indeed. Just follow up with these results, and after that we will move to testing other parts of the PSU. I suspect either D101 and/or D102 are shorted -OR- there is a short-circuit behind them... though as to why the controller doesn't have a pulsing voltage on Vdd (to indicate fault-restart operation), that's another thing to worry about.


No, never run a circuit with parts missing, unless you very well know what those parts do and know that the circuit will be okay without them. This rarely happens, because if the manufacturer didn't need to put that part there, they wouldn't - after all, having to put less parts also means lower production cost for them, so they would have left it out if it could be left out.

[lcdcaps1]

Re: GNR TS902W no power , help please

Ok so i replaced the diode rectifier, highlighted in attached pic
i tested it in diode mode and outside and it was not working as a diode
one side was working but other so i checked outside of board and also

so changed it out with a new one and still no voltage on the startup plus no output voltage still
No pwm controller chip voltage

is it possible that the pwm chip is gone dead again or is it a capacitor or a mosfet/transistor

Hi All
So I took the diodes out.
D101, D102 and D105
All test ok in one direction,
Black probe on band and red on other end and nothing in other way
(red probe on band and black probe on other end)

Tested for shorts as well and no shorts
below are results of diodes, (black probe on band and red probe on other end)

D101
0.169V

D102
0.172V

D105
0.469V

Q103 readings below

between Base and Emitter (with black probe on Emitter)
0.635v
between Base and Collector (with black probe on Collector)
0.618v

between Collector and Emitter (black probe is on Emitter.)

no reading shown if black probe is on emitter and red probe is on collector

If i switch probes around,
red probe on emitter and black probe on collector, i get reading
0.575v

Please can someone tell me if these diodes are ok
thanks all

[lcdcaps1]

Re: GNR TS902W no power , help please

I have been reading about TL431 which may cause no power on LCD monitors
but was wondering before i replace this with another one is there anything else that could cause no power

also is my transistor ok, the one on the heat sink

[momaka]

Re: GNR TS902W no power , help please

So I took the diodes out.
D101, D102 and D105
All test ok in one direction,
Black probe on band and red on other end and nothing in other way
(red probe on band and black probe on other end)

Tested for shorts as well and no shorts
below are results of diodes, (black probe on band and red probe on other end)

D101
0.169V

D102
0.172V

D105
0.469V

Q103 readings below

between Base and Emitter (with black probe on Emitter)
0.635v
between Base and Collector (with black probe on Collector)
0.618v

between Collector and Emitter (black probe is on Emitter.)

no reading shown if black probe is on emitter and red probe is on collector

If i switch probes around,
red probe on emitter and black probe on collector, i get reading
0.575v

Please can someone tell me if these diodes are ok

Yup, they seem to be fine now.

Ok so i replaced the diode rectifier, highlighted in attached pic
i tested it in diode mode and outside and it was not working as a diode
one side was working but other so i checked outside of board and also

How did you test it? What readings did you get?
Rectifiers like that have the middle pin as a common-cathode. That is, the leftmost and rightmost pins are the anodes of two diodes, and their cathodes join in the middle pin (hence the term common-cathode).

To test a rectifier like that (out of circuit), put black multimeter probe on middle pin (cathode). Then check that you get a diode reading when you put the red multimeter probe on the left pin and then the right pin. Both should show similar diode readings. If you reverse the probes, you should get no reading (open-circuit).

so changed it out with a new one and still no voltage on the startup plus no output voltage still
No pwm controller chip voltage

is it possible that the pwm chip is gone dead again or is it a capacitor or a mosfet/transistor

Well, it's also possible that you new PWM chip is bad too. Very small chance, but I just don't see why else you wouldn't have a voltage on the Vdd pin. Also, if I remember correctly, you said after putting the new PWM controller, pin 3, Vin had no voltage on it. Can you check that again and post what voltage it has? If there's no voltage on that pin, then nothing would work.

In any case, before you go plug in your power supply again after you replace something, first build yourself a series incandescent bulb device and connect it like this:
https://www.badcaps.net/forum/showpo...4&postcount=70
That way, if something is wrong with the power supply, it won't blow up your fuse or any other parts and should keep things like your new PWM controller fairly safe.

Because I forgot to post here that you should use the series incandescent bulb every time you power the PSU, just quickly re-check all your components on the primary side again, like the main fuse, bridge rectifier, and MOSFET. You don't need to post their values.

For the MOSFET, just make sure it had a diode reading when you put black probe on Drain and red probe on Source. Reversing the probes should show open-circuit after a few seconds (as the mains cap can fool your multimeter while the meter is charging it). Resistance from Gate to Source or Drain should also be fairly high in circuit and completely open-circuit if the MOSFET is removed from the board and measure that way.

I have been reading about TL431 which may cause no power on LCD monitors
but was wondering before i replace this with another one is there anything else that could cause no power

Yes, TL431 shunt IC can cause no power. However, we should still see some voltage on pin Vdd of the PWM IC - and we are not seeing that, so that's the worrysome part.

That said, check the output (primary) side of the opto-coupler, U102. One side should be connected to pin 2 (FB) of the SG6841 PWM controller, the other to primary-side ground (negative lead on primary cap). With that said, check what resistance you get between pin 2 of the SG6841 IC and primary-side ground, then post the results here. If the opto-coupler is bad, that could be causing the no power issue as well.

Other things I can think of is if there is something shorted on the secondary side after the output rectifiers (like the CCFL inverter driver transistors)... but again, I think even that should allow the SG6841 IC to have some voltage on its Vdd pin and the power supply outputs to be pulsing.

[lcdcaps1]

Re: GNR TS902W no power , help please

Hi
Thanks for this. I'll get onto this later.
I tested the diode rectifier the same way you mentioned
The original one when testing like you said would work but only one side and all three pins were short
So replaced

How can i make sure the transistors are not shorted on the secondary side

Thanks again

Yup, they seem to be fine now.


How did you test it? What readings did you get?
Rectifiers like that have the middle pin as a common-cathode. That is, the leftmost and rightmost pins are the anodes of two diodes, and their cathodes join in the middle pin (hence the term common-cathode).

To test a rectifier like that (out of circuit), put black multimeter probe on middle pin (cathode). Then check that you get a diode reading when you put the red multimeter probe on the left pin and then the right pin. Both should show similar diode readings. If you reverse the probes, you should get no reading (open-circuit).


Well, it's also possible that you new PWM chip is bad too. Very small chance, but I just don't see why else you wouldn't have a voltage on the Vdd pin. Also, if I remember correctly, you said after putting the new PWM controller, pin 3, Vin had no voltage on it. Can you check that again and post what voltage it has? If there's no voltage on that pin, then nothing would work.

In any case, before you go plug in your power supply again after you replace something, first build yourself a series incandescent bulb device and connect it like this:
https://www.badcaps.net/forum/showpo...4&postcount=70
That way, if something is wrong with the power supply, it won't blow up your fuse or any other parts and should keep things like your new PWM controller fairly safe.

Because I forgot to post here that you should use the series incandescent bulb every time you power the PSU, just quickly re-check all your components on the primary side again, like the main fuse, bridge rectifier, and MOSFET. You don't need to post their values.

For the MOSFET, just make sure it had a diode reading when you put black probe on Drain and red probe on Source. Reversing the probes should show open-circuit after a few seconds (as the mains cap can fool your multimeter while the meter is charging it). Resistance from Gate to Source or Drain should also be fairly high in circuit and completely open-circuit if the MOSFET is removed from the board and measure that way.


Yes, TL431 shunt IC can cause no power. However, we should still see some voltage on pin Vdd of the PWM IC - and we are not seeing that, so that's the worrysome part.

That said, check the output (primary) side of the opto-coupler, U102. One side should be connected to pin 2 (FB) of the SG6841 PWM controller, the other to primary-side ground (negative lead on primary cap). With that said, check what resistance you get between pin 2 of the SG6841 IC and primary-side ground, then post the results here. If the opto-coupler is bad, that could be causing the no power issue as well.

Other things I can think of is if there is something shorted on the secondary side after the output rectifiers (like the CCFL inverter driver transistors)... but again, I think even that should allow the SG6841 IC to have some voltage on its Vdd pin and the power supply outputs to be pulsing.

[rddube]

Re: GNR TS902W no power , help please

I have been reading about TL431 which may cause no power on LCD monitors
but was wondering before i replace this with another one is there anything else that could cause no power

also is my transistor ok, the one on the heat sink

The way I test transistors is out of circuit with a transistor tester - it actually gives you a drawing of the transistor so you know it's good. Do you have one of those?

Something like this: https://www.ebay.com/itm/Transistor-...QAAOSwsXFZE0dC

At some point you mentioned that you have voltage on one of the legs of that transistor, what about the other legs?

[lcdcaps1]

Re: GNR TS902W no power , help please

hi thanks for the reply
i have one of these

https://www.dhresource.com/0x0s/f2-a...inductance.jpg

Its similar to the link you provided,
Maybe different model number

The only pin i have voltage is drain
but I will go through the tests that was provided by Momka
I just find this very weird why there is no voltage on the startup cap

I think i will remove the transistor on the heatsink and test out of circuit
then follow momka tests

If anyone has any other ideas or has seen this before then please let me know
thanks in advance

This monitor was working fine and one day did not turn on at all
no front light nothing and there is no voltage on the output ribbon cable

Did not have any power cuts or spill anything
just randomly dead

Really appreciates everyone's help and more to come
please

Thanks

The way I test transistors is out of circuit with a transistor tester - it actually gives you a drawing of the transistor so you know it's good. Do you have one of those?

Something like this: https://www.ebay.com/itm/Transistor-...QAAOSwsXFZE0dC

At some point you mentioned that you have voltage on one of the legs of that transistor, what about the other legs?

[lcdcaps1]

Re: GNR TS902W no power , help please

Hi
there is no voltage on the optocoupler
i tested using diode mode and it is functioning ok

I tested resistance from pin 2 (SG6841) to the negative side of the big cap
and there is no short got a high resistance reading

Yup, they seem
to be fine now.


How did you test it? What readings did you get?
Rectifiers like that have the middle pin as a common-cathode. That is, the leftmost and rightmost pins are the anodes of two diodes, and their cathodes join in the middle pin (hence the term common-cathode).

To test a rectifier like that (out of circuit), put black multimeter probe on middle pin (cathode). Then check that you get a diode reading when you put the red multimeter probe on the left pin and then the right pin. Both should show similar diode readings. If you reverse the probes, you should get no reading (open-circuit).


Well, it's also possible that you new PWM chip is bad too. Very small chance, but I just don't see why else you wouldn't have a voltage on the Vdd pin. Also, if I remember correctly, you said after putting the new PWM controller, pin 3, Vin had no voltage on it. Can you check that again and post what voltage it has? If there's no voltage on that pin, then nothing would work.

In any case, before you go plug in your power supply again after you replace something, first build yourself a series incandescent bulb device and connect it like this:
https://www.badcaps.net/forum/showpo...4&postcount=70
That way, if something is wrong with the power supply, it won't blow up your fuse or any other parts and should keep things like your new PWM controller fairly safe.

Because I forgot to post here that you should use the series incandescent bulb every time you power the PSU, just quickly re-check all your components on the primary side again, like the main fuse, bridge rectifier, and MOSFET. You don't need to post their values.

For the MOSFET, just make sure it had a diode reading when you put black probe on Drain and red probe on Source. Reversing the probes should show open-circuit after a few seconds (as the mains cap can fool your multimeter while the meter is charging it). Resistance from Gate to Source or Drain should also be fairly high in circuit and completely open-circuit if the MOSFET is removed from the board and measure that way.


Yes, TL431 shunt IC can cause no power. However, we should still see some voltage on pin Vdd of the PWM IC - and we are not seeing that, so that's the worrysome part.

That said, check the output (primary) side of the opto-coupler, U102. One side should be connected to pin 2 (FB) of the SG6841 PWM controller, the other to primary-side ground (negative lead on primary cap). With that said, check what resistance you get between pin 2 of the SG6841 IC and primary-side ground, then post the results here. If the opto-coupler is bad, that could be causing the no power issue as well.

Other things I can think of is if there is something shorted on the secondary side after the output rectifiers (like the CCFL inverter driver transistors)... but again, I think even that should allow the SG6841 IC to have some voltage on its Vdd pin and the power supply outputs to be pulsing.

[lcdcaps1]

Re: GNR TS902W no power , help please

I removed the mosfet from the heat sink and board with the component tester
it tested ok within spec

no voltage on the optocoupler but tested ok in diode mode

Hi
there is no voltage on the optocoupler
i tested using diode mode and it is functioning ok

Also no vdd on the pwm controller chip

I tested resistance from pin 2 (SG6841) to the negative side of the big cap
and there is no short got a high resistance reading

[rddube]

Re: GNR TS902W no power , help please

If you go back a couple of posts, I mentioned that on the solder side of your board, there seemed to be a spot where it heated, near the transistor. How bad is the heat spot when you examine it closely?

I would check all components in that area and would take out the mosfet (transistor) and test it with your transistor tester.

[rddube]

Re: GNR TS902W no power , help please

I removed the mosfet from the heat sink and board with the component tester
it tested ok within spec

no voltage on the optocoupler but tested ok in diode mode

Ok, check the other components that are near that heat spot out of circuit if possible.

[lcdcaps1]

Re: GNR TS902W no power , help please

ive checked all those components
examined the components, it seemed to me that the solder joint was not great
but did not look like over heating

looked over the smd components

what else could cause no voltage output

Ok, check the other components that are near that heat spot out of circuit if possible.

[rddube]

Re: GNR TS902W no power , help please

It's a little difficult to tell without the schematics. But I would open the schematics I posted in a previous post (it is not exactly your board but it is very close), and starting at the AC input would trace where I should find voltage.

The labels on the components in the schematics are not exactly the same as on your board but you have the type of component and you could cross-reference it to your actual board. At some point, you're going to hit a spot where you should be having voltage and you don't. The component just before that spot will probably be your culprit.

BTW, you say you have voltage on the big cap? Did you check that caps ESR?

[lcdcaps1]

Re: GNR TS902W no power , help please

what would be a good esr for the big cap

It's a little difficult to tell without the schematics. But I would open the schematics I posted in a previous post (it is not exactly your board but it is very close), and starting at the AC input would trace where I should find voltage.

The labels on the components in the schematics are not exactly the same as on your board but you have the type of component and you could cross-reference it to your actual board. At some point, you're going to hit a spot where you should be having voltage and you don't. The component just before that spot will probably be your culprit.

BTW, you say you have voltage on the big cap? Did you check that caps ESR?

[lcdcaps1]

Re: GNR TS902W no power , help please

Could the problem i am facing be a transformer issue

[rddube]

Re: GNR TS902W no power , help please

It could be the transformer, what voltages do you get on it (be careful again). ESR for the big cap should be low, lower than 2 ohms, best is below 1 ohm.

[lcdcaps1]

Re: GNR TS902W no power , help please

The esr for the big cap is 0.91
Ive replaced the opto and tl431 to rule out

Attached is pic that has high lighted in yellow the pins i get voltage on. This is one side of the yellow transformer that has delta writing on top. Also high lighted other pins where i get voltage

i get 328 v dc on the pins mentioned above
but nothing on other side

Could the thermal fuse inside the transformer be bad.
Thanks again all

It could be the transformer, what voltages do you get on it (be careful again). ESR for the big cap should be low, lower than 2 ohms, best is below 1 ohm.

[lcdcaps1]

Re: GNR TS902W no power , help please

ok so a bit of an update
i replaced the pwm chip again

now i get
on pin 3
22.70 v

on pin 7
1.1v

also startup cap has some voltage
1v