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Old 06-04-2018, 09:21 AM   #101
budm
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Default Re: Need schematic for Visio LC420

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Originally Posted by jkb242 View Post
There isn't a BL on pin, there is a Lamp pin but I thought that was not for turning on/off the BL but used to monitor the lamp? Is that incorrect?
But what pin did you use to force on the backlights? I already indicated that I ON/OFF is the same as BL-ON.
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http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

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Old 06-04-2018, 09:24 PM   #102
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Default Re: Need schematic for Visio LC420

Sorry I forgot but I confirmed that if PSON is not connected to the 5vstby rail, the 12vdc will disappear along with the signal measured at T703. The supply of the Toshiba power Mosfets has nearly dried up. I have not determined these inventor switchers are bad by diode checking as most of my free time today was removing the shield to gain access. Got any sources for these if I find a bab one. Like replace in pairs. Any discovery on the PWM chip we have both been looking to get the pin outs?

BTW, the Ion/off is connected but did not remove the 5v to see if was any effect on the drive signal.
Thanks
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Old 06-04-2018, 10:16 PM   #103
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Default Re: Need schematic for Visio LC420

At this point it sounds to me that the PWM IC is working and it is driving the Gate drive transformers. BTW, are you working on the original power supply board or the replacement power supply board?
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Old 06-05-2018, 06:45 AM   #104
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Default Re: Need schematic for Visio LC420

The replacement. I have a few missing parts on the original board that I am replacing from my last Digikey order that has not yet arrived bringing it back to its original condition. I also have the replacement board from SJ I have not yet returned. I will be making the same checks on my original board to see if it is at least on par with the replacement.

I wish I had an isolation transformer so I could use my scope to check the intermediate driver transistors on the secondary side. There isn’t much left her but the final power MOSFETS, it’s just seems quite odd that all three boards would suffer these specific failures.

As you say, the PWM IC seems to be working but that waveform sure contains overshoot artifacts I wouldn’t have expected. Could be my probe trimming as well. I’ll report back on the diode test modes of the driver FETs.
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Old 06-09-2018, 07:06 AM   #105
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Default Re: Need schematic for Visio LC420

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OK, so the switched Transistors are turned on and supplying the Voltages, one end of those two resistors should go to the VCC pin of the PWM IC.
It sounds like the IC is working, you can disconnecting the the BL-ON force on resistor to see if the 45Hz will go away or not, I actually expecting higher frequency than that.
BTW, what is the LCD panel model number?
What frequency were you expecting from your experience within what typical range.

Thanks
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Old 06-09-2018, 04:34 PM   #106
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Default Re: Need schematic for Visio LC420

50KHz ~80KHz.
45KHz may be OK, at this point we know that we are getting the drive Voltage to drive the Gates of the MOSFETs so the MOSFETs should be switching right now.
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Old 06-13-2018, 06:47 PM   #107
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Default Re: Need schematic for Visio LC420

Further testing on power MOSFETs show that all four TK4A60DA drivers measure the same using simple power or switching action using diode mode on DVTM. This includes Q701,706,715, 720.

Q801, 802 are both K3569 now replaced by 2Sk3569 measured differently exhibiting source to drain full conduction to a gradual isolation state without discharging the gate. Both devices measured the same.

I did not replace the TK4A60DA devices even though I had new devices on hand but did not have the 2Sk3569 so I was unable to compare the original devices with the new ones. My question at this point would be given the drive level and power of this application, is the diode mode testing completely valid from your experience.

Please advise.

Thanks!!
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