Sharp Aquos 80" not working

[Markus66]

Re: Sharp Aquos 80" not working

Sorry, I mean IC7201 in the hot side of the circuit.

I just pulled the spec sheet for IC7201 - TI UCC28061

This is beyond my basic TTL skillset. I have no idea what to look for. Looking at the block diagram, I cannot even predict what I should be seeing at any given pin. I am so stuck in the '70s....

[budwich]

Re: Sharp Aquos 80" not working

:-)

Budm will likely show up eventually... but in the mean time, the pdf for that IC has the "functional description" for each pin in the IC. You likely need to very some of those pins. Focus on one that have voltages associated with them... they give ranges / expectations for the operation. BE CAREFUL, there is the HOT side which has large voltages on it which can kill you. Further, look very carefully at the board and pins... the pins are very close together... try to find places where you can safely probe.

Lastly, page 8 (on my view) shows most of the voltages and indicates things like "brown out" which turns the functioning behind the IC off for protection. That might be one area to check along with the other voltages listed there. Quick read of the other functions show over voltage protection also which might need investigation. Was the set / did the set see any kind of power "hits".

[dick_barton]

Re: Sharp Aquos 80" not working

You could check the following voltages on that IC.

According to the data sheet Pin 12 (VCC) should be between 14V DC min and 21V DC max and Pin 15 (Vref) should be at 6V DC.

Pin 7 (VINAC) should be approximately 2V DC

Connect the black meter lead to the negative (-) leg of any of the high voltage capacitor (either C7220, C7222 or C7223) when making the
measurement.

This is the live (HOT) side of the power supply so take care that your meter probes do not slip.

[Markus66]

Re: Sharp Aquos 80" not working

You could check the following voltages on that IC.

According to the data sheet Pin 12 (VCC) should be between 14V DC min and 21V DC max and Pin 15 (Vref) should be at 6V DC.

Pin 7 (VINAC) should be approximately 2V DC

Connect the black meter lead to the negative (-) leg of any of the high voltage capacitor (either C7220, C7222 or C7223) when making the
measurement.

This is the live (HOT) side of the power supply so take care that your meter probes do not slip.

OK. Kids are out of the house so I have a chance to play around with this a bit.


Pin 12 (Vcc). - 14.93 VDC

Pin 7 (VINAC) - 3.32 VDC

Pin 15. (VREF). - 0 VDC. - Nothing


Voltages measured in reference to neg lead on main filter cap as requested.

Hope these results along with the low (165VDC) voltage at the filter caps might point to something going on.


Thanks,
Mark

[Markus66]

Re: Sharp Aquos 80" not working

:-) Was the set / did the set see any kind of power "hits".

Not that I'm aware of. We do live in the country and it is possible I suppose but there is nothing else in the house showing any signs of disruption

[budwich]

Re: Sharp Aquos 80" not working

i think you might as well start checking why there is no vref.

[dick_barton]

Re: Sharp Aquos 80" not working

Pin 12 (Vcc). - 14.93 VDC

Pin 7 (VINAC) - 3.32 VDC

Pin 15. (VREF). - 0 VDC. - Nothing


Voltages measured in reference to neg lead on main filter cap as requested.

Hope these results along with the low (165VDC) voltage at the filter caps might point to something going on.


Thanks,
Mark

VCC supply is within the operating range and VINAC appears to closely match the data sheet since it's not less than 2V. However VREF should be a regulated output from the IC supplying 6V and will only switch off if VCC does not reach it's operational level.

Is the VREF pin connected to other components?

What is the voltage on PIN 2 (VSENSE) and Pin 8 (HVSEN)

[Markus66]

Re: Sharp Aquos 80" not working

The VREF seems to be connected to pin 2 on a SSC9512S chip through a couple resistors and a cap.

I will record voltages on the rest of the pins on both chips when I get a minute tomorrow.

I can only find a pinout for the 16 pin DIP and not the 18 pin (SSC8512S) surface mount - I'll dig a bit more for that.

Thanks
Mark

[Markus66]

Re: Sharp Aquos 80" not working

So, I pulled D7112 to check it and it's open. It was testing shorted in circuit - power off.

It is labelled T3D 16

I think this is a zener and is likely OK I'm guessing...


Back to voltages on the little surface mount ICs.

[budwich]

Re: Sharp Aquos 80" not working

hmmm... not sure about that. I thought that a zener should test with the "diode check" in one direction... while in the other depending on the voltage may not.

[Markus66]

Re: Sharp Aquos 80" not working

hmmm... not sure about that. I thought that a zener should test with the "diode check" in one direction... while in the other depending on the voltage may not.

Keep in mind I really don't know what I'm doing...

My knowledge is self taught and very limited.

So, now that I have already soldered the diode back in, should I be actually replacing it?

If that diode is indeed bad, should there be something else that caused it and/or will it have caused something else to go bad as well?


Edit: Also, since it seems to be a protection diode of sorts, even if it is bad, would it keep the circuit from working?

[budwich]

Re: Sharp Aquos 80" not working

I don't know either... :-) just going by my "basics".... for diodes. Basically, a zener acts like a diode in the biased direction and "holds a voltage" in the other as opposed to being totally blocked like normal diode. That "hold" may actually be the "Vref" in this case (depending on the circuit) which could be the 6V as was suggested. Perhaps the zener is a "06" maybe... meaning 6V.

In circuit testing is "tough" unless you know what the other portions of the circuit are (ie. components, connections). Further, when you tested it out of circuit, how did you do that... resistance check? diode check? Still further, in circuit, your "short" result might have been telling you something about the "rest of the circuit"... and might be the reason why the diode is "done". With the diode removed you should do that same test of the circuit that you did before... if you get "short" again.... there is something wrong there.

[Markus66]

Re: Sharp Aquos 80" not working

I tested the diode with the diode function on two different fluke meters just to be sure when it was out of circuit. Showed bad.

It's shorting in circuit because it is installed across the primary winding of a small transformer. So, that makes sense.

I have a few general purpose diodes but no zener diodes. I will have to order one I guess.

[budwich]

Re: Sharp Aquos 80" not working

OK... that makes sense then as it is probably providing "well defined" voltage towards the transformer which then has secondaries which are dropping (or otherwise) as needed.

[Markus66]

Re: Sharp Aquos 80" not working

OK. I guess I need to replace the zener diode T3D16

I cannot suss out the specs on this one. Can someone help with this so I can find and equivalent replacement.


Thanks,
Mark

[R_J]

Re: Sharp Aquos 80" not working

I believe it is a tvs diode, it will check open on diode test, Likely similar to a P6KE200
I think the marking is T3D and 16 is a date code

[budm]

Re: Sharp Aquos 80" not working

It is back to back diodes (Diode + Zener with, the Cathode of each diode are connected together, the two leads are the Anode of each diode, you cannot test it with diode mode, it will show open circuit. if it is bad it the MOSFET that drive the transformer will be damaged, it is snubber diode.
As I already indicated in post #18 that D7112 is for the standby power supply and it is working because you do have the standby Voltage 5V so put the diode back in place and make sure the standby Voltage is still present, it is the 13V power supply section that needs in-depth troubleshooting.
I do not have the time to look at the spec sheet of the IC7201 yet or tracing out the board.