Westinghouse 46" Model VR-4625-Need Help

[budm]

Re: Westinghouse 46" Model VR-4625-Need Help

budm, I get what your saying but i for the life of me can not see which one it is...can it be seen in my pictures?

I can easily spend couple hours if I have the board in front of me to trace out the connection and draw up the diagram.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

budm, could it be this transistor? Its marked Q1, D1616AL(TRANS) NTE Equvilent NTE382 T-NPN SI AF DRIVER

See picture. The negative probe is pointing to the transistor.

[budm]

Re: Westinghouse 46" Model VR-4625-Need Help

I cannot tell, if you look at the example circuit, it will give you some idea how the Emitter and the Collector should be connected.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

I cannot tell, if you look at the example circuit, it will give you some idea how the Emitter and the Collector should be connected.

thanks budm, I think I have traced the VSS problem back to a small transistor (see picture for details). When the outputs are on the Emitter is sending out ~13 volts, tracing it out the emitter is connected to both the L6562A &L6599AD VSS pins. In addition when the outputs shut down the Emitter reads zero volts and the collector reads ~16 volts (which is an increase from the 13 v at the collector when its operating).

Is it safe to assume this transistor could be the root of the problem?

[budm]

Re: Westinghouse 46" Model VR-4625-Need Help

OK, so then we need to find out if the transistor is being commanded to turn on or not. You need to check the DC voltage between the Base and Emitter, it should have around 0.6~0.7V when it is on, if it does not, then you will need to trace out the BASE connection.
As you can see in the sample circuit, the transistor is turned on by the Opto-Isolator.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

OK, so then we need to find out if the transistor is being commanded to turn on or not. You need to check the DC voltage between the Base and Emitter, it should have around 0.6~0.7V when it is on, if it does not, then you will need to trace out the BASE connection.
As you can see in the sample circuit, the transistor is turned on by the Opto-Isolator.

Budm, the base&emitter have .618 v when the out puts are on, when the outputs go out there is 16v found on Base&emitter and base collector. Does that point to the transistor or do I need to chase it farther?

*Under normal circumstances I would troubleshoot the problem to the board and just replace the faulty board. This one is an exception I wanted a challenge but the problem is so intermittent. I am closing in on the end of my patients with it.

[budm]

Re: Westinghouse 46" Model VR-4625-Need Help

The transistor is an NPN. It sounds like the Emitter-Base junction of the transistor went open circuit when the circuit stops working.
You can try replacing that transistor, you can use through hole type, just have to be good at soldering.
For example of my repair of FSP power supply with about the same setup of yours with bad transistor:
http://s807.photobucket.com/user/bud...ml?sort=3&o=27

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

I think I FINALLY found it...when the outputs shut down, I placed a small (104) capacitor across an smd capacitor ( no idea what size) and the outputs turned back on without a power cycle. I have done this a few times to confirm that its that...and it seems to be. I plan to solder the 104 capacitor over the smd. I appreciate all the input.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

I hope this thread helps someone with similar problems. My last post is to clarify that adding the capacitor (104) over the smd cap (100pf) did not fix the problem. It only identified the problem. The fix was to remove the capacitor (smd one) and add a shunt in its place.

[budm]

Re: Westinghouse 46" Model VR-4625-Need Help

Can we see the picture of this section? BTW, SMD caps are not labeled, how did you figure out it is 100pF? Changing from 100pF to 0.1uF (104?) does not make sense.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

I de-soldered and tested the smd capacitor using caps mode on my DVM.

I have attached a picture showing the location of the repair. My tv is back together and kids are watching, i am unable to get a final pictures showing the actual repair.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

Can we see the picture of this section? BTW, SMD caps are not labeled, how did you figure out it is 100pF? Changing from 100pF to 0.1uF (104?) does not make sense.

Hi Budm, sorry I missed the rest of your questions yesterday (mobile phone displays are limiting). As for testing the capacitor to find the value, the problem was intermittent and as such once the capacitor cools off I got a reasonably close reading to 100 pF using my DVM. I assume once it heated up it would break down and read something else in circuit.
Changing the 100pF to a 100,000pF does not make sense, as I did not replace it with the 104 capacitor as my post above states. Using the 104 cap (just something I had lying on the bench) was the means by which I found the problem. I assume if i had a 100 pF capacitor (SMD style) I would replace it "in kind" but the shunt does the trick. The tv has been in use for well over 24 hours and the fix seems to be holding. thanks for all your input.

[budm]

Re: Westinghouse 46" Model VR-4625-Need Help

I am just trying to understand how that cap is connected and what its function is in the circuit. We know that the transistor failed to put out the voltage to feed the ICs. I could not tell from the pictures on how that cap is connected. But its good that the TV is working. I just like to analyze and understand how things work.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

I am just trying to understand how that cap is connected and what its function is in the circuit. We know that the transistor failed to put out the voltage to feed the ICs. I could not tell from the pictures on how that cap is connected. But its good that the TV is working. I just like to analyze and understand how things work.

The best I can do now is attempt to draw out the circuit on an existing picture, since the board is not accessible. See the picture attached.

Here is what I know and tried to portray in the photo. The two mosfet drain leads, one 12V the other 24V lead to an array of small SMD transistors.All of the transistors seem to function through this one capacitor (12,24 &5V). Once the outputs would shutdown, I would then use a random capacitor in this case the 104 cap to jumper the suspect smd capacitor. This would cause the output to turn back on and stay running for a while then shutoff again, repeat the process and I could then make the problem appear and disappear at will. I hope this helps, I drew a schematic on paper but threw it out yesterday.

[pbones]

Re: Westinghouse 46" Model VR-4625-Need Help

Additionally, the 5V outputs (S5V, STBY, 5V) were not affected as they did not function through this smd cap, anything on the high voltage side would be affected as the 5V traveled through the SMD cap to power those chips.