Vizio VW42LFHDTV10...Brother Mikes TV...

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...waiting for parts

At this point I'm awaiting the replacement inverter boards, to see what they read and do. It would be of great help if we had any schematics on these, so that someone could help interpret the way the boards feed each other, and where the critical voltage checks are. For now it appears that the boot up requires certain critical working parts on ALL 5 boards during its posting.

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...ready to try 'new' inverters

I got the replacement inverter boards today and ran some resistance and capacitance checks while all 4 boards were out side by side. The fuses were all OK, the transformers read 1250 ohms for the new and 1350 for the old, the fets on the new boards were all about 10% higher at 4000-4200 ohms for the slave, while the new master had two at 5000 and 5800 ohms, again all about 10% higher than the old ones. All the caps read 0.01 ESR and 930-950uf in circuit for the 470ufx35v spec. The only measurement I took that wasn't close or within 10% was the cap resistance, the old master caps read 495 ohms while the new ones are 440, but the biggest difference was the old slave caps read 550 ohms while the new slave caps read only 340 ohms, a 60% difference.

Not sure I proved much short of trying them on the set...but before I do does anyone have any further checks or advice on proceeding with the swap ??

[Dgtech]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...

Make sure you mark the old ones somehow with a marker so you know the difference between the new ones. Put them in and try them. See what you got.

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...Inverters not bad

Well as I suspected the problem is apparently not at this point on the inverters. Tried both of my replacements on set and saw no change in problem at all. Time to restart the analysis(?):
Since I have all the required output voltages from the power board, both 5v stand by, and 12 and 24v when kicked up, and since voltages are steady, is there any reason to think that there is trouble with the power supply board? All the caps are good brands and read low ESR's in circuit. I haven't pulled any or changed any on power supply....but is there any chance one is bad and is acting up to cause this no boot ?
That leaves the T-Con and Mainboard as suspects which no doubt have feedback controls, so if voltage is switching on me no doubt it is from something on these boards?
As for the T-Con I only tried it dis-connecting to no avail, but no measurements were taken.
Then there is the Mainboard which I've suspected from the beginning....and so does PlainBill. In my prior posts I probed all the caps and replaced 6, with no change. Also I read many of the voltages including the 5 LDO regulators (see my post #28 and 29 this thread ) several of these readings seem to be out of spec. Then there is the one repair here that did the U33 Fet at my post #26.
Does anyone have a better idea of the main-board workings to help locate which components are afoul ?

[PlainBill]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...Inverters not bad

Well as I suspected the problem is apparently not at this point on the inverters. Tried both of my replacements on set and saw no change in problem at all. Time to restart the analysis(?):
Since I have all the required output voltages from the power board, both 5v stand by, and 12 and 24v when kicked up, and since voltages are steady, is there any reason to think that there is trouble with the power supply board? All the caps are good brands and read low ESR's in circuit. I haven't pulled any or changed any on power supply....but is there any chance one is bad and is acting up to cause this no boot ?
That leaves the T-Con and Mainboard as suspects which no doubt have feedback controls, so if voltage is switching on me no doubt it is from something on these boards?
As for the T-Con I only tried it dis-connecting to no avail, but no measurements were taken.
Then there is the Mainboard which I've suspected from the beginning....and so does PlainBill. In my prior posts I probed all the caps and replaced 6, with no change. Also I read many of the voltages including the 5 LDO regulators (see my post #28 and 29 this thread ) several of these readings seem to be out of spec. Then there is the one repair here that did the U33 Fet at my post #26.
Does anyone have a better idea of the main-board workings to help locate which components are afoul ?

There are a few things you can check on the main board.

1. Check the voltage regulators and make sure the output voltage is correct

2. Check any SMT fuses

3. Look the board over carefully for any damaged (scorched) components.

PlainBill

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...LDO regulators

Bill...
Here's the sheet for my LDO regualors; Am I right that without a voltage spec on them they are the adjustable types ?:

http://pdf1.alldatasheet.com/datashe...C/AMC1117.html

My re-calibrated readouts:
fet....V.in (leg 1-3)-- leg 2-3)--V.out (leg 1-2):
U2.... 3.0 VDC-- 1.8V --- 1.2V
U7.... 3.5 --- 2.3 --- 1.1
U8.... 3.0 --- 1.9 --- 1.25
U9.... 3.5 --- 1.8 --- 1.5
U33... 3.0 --- 1.8 --- 1.25

4 of these are AMC1117 F0646J ; U9 is a K1117S15 612

Is leg 1-2 the output ? what is the measure across legs 2-3 called?
What's up with my U7 and U9's ?

[PlainBill]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...LDO regulators

Bill...
Here's the sheet for my LDO regualors; Am I right that without a voltage spec on them they are the adjustable types ?:

http://pdf1.alldatasheet.com/datashe...C/AMC1117.html

My re-calibrated readouts:
fet....V.in (leg 1-3)-- leg 2-3)--V.out (leg 1-2):
U2.... 3.0 VDC-- 1.8V --- 1.2V
U7.... 3.5 --- 2.3 --- 1.1
U8.... 3.0 --- 1.9 --- 1.25
U9.... 3.5 --- 1.8 --- 1.5
U33... 3.0 --- 1.8 --- 1.25

4 of these are AMC1117 F0646J ; U9 is a K1117S15 612

Is leg 1-2 the output ? what is the measure across legs 2-3 called?
What's up with my U7 and U9's ?

I suggest measuring the voltage in a different manner. That will make it easy to determine what is going.

Choose a suitable ground point - I tend to favor things like mounting screws, shields, or the negative lead of a capacitor. Measure the voltage from Ground to pins 1, 2, 3.

On a fixed output regulator (U9) pin 1 is Gnd, pin 2 is Vout, pin 3 is Vin. On the variable output regulators I expect to see a consistent voltage drop between pins 1 and 2 - typically 1.2 or 1.25 volts. U7 appears to be faulty.

PlainBill

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...LDO regulators

Here are the pin readings to chassis ground:
fet....pin 1 gnd -- pin 2 V.out --pin 3 V.in
U2.... 2.0 VDC -- 3.3V -- 5.1V
U7.... 0.0 --- 1.0 --- 3.4
U8.... 2.0 --- 3.3 --- 5.2
U9.... 0.0 --- 1.5 --- 3.4 <.....fixed LDO 1.5V
U33... 2.1 --- 2.8 --- 5.1

I doubled checked these readings, and my meter and the supply...are you sure about the 1.2-1.25 VDC outputs on the adjustables ?

[hoadle]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...

Dear kingofcoins
My problem so different what you had
I follow the pot (is same problem & model #) Plus T/S at chapt 9 Service manual check all LDO regualors
find out my U33 had input 12Vdc & output 3.3V when I changer the new one (at old U33 input 12V but output is 2.5V only)

[PlainBill]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...LDO regulators

Here are the pin readings to chassis ground:
fet....pin 1 gnd -- pin 2 V.out --pin 3 V.in
U2.... 2.0 VDC -- 3.3V -- 5.1V
U7.... 0.0 --- 1.0 --- 3.4
U8.... 2.0 --- 3.3 --- 5.2
U9.... 0.0 --- 1.5 --- 3.4 <.....fixed LDO 1.5V
U33... 2.1 --- 2.8 --- 5.1

I doubled checked these readings, and my meter and the supply...are you sure about the 1.2-1.25 VDC outputs on the adjustables ?

If you check the datasheet for the AMC1117 you will see the output voltage for the adjustable regulator is Vout= 1.25 x (1+ R2 / R1). R1 is connected between the output pin (pin 2) and the Adj pin (pin 1). If you do the math, you will see there will always be 1.25V between pin 2 and pin 1 when the regulator and the load are working properly. U9 is the fixed output regulator. Look at U2 and U8 - 1.3 volts. U7 is strange. If pin 1 were grounded I would expect 1.25 volts out. Clearly something is wrong. Also U33's readings indicate a problem. If Pin 1 is at 2.1 volts, pin 2 should be at 3.3 volts.

PlainBill

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...voltage regulators

Very good Bill, many of us need a mentor like you so we can then 'do the math'.. thanks for the explanation.
So then these LDO voltage regulators do play a key role in the system start-up and no doubt also control the back lights, and other functions. Without a good schematic I see what your saying its hard to know what is doing what.
That U33 has been a popular failure with Vizio, at least with this series of main boards. And now I agree my U7 is out of whack. I see why U9 is different and OK, and also from the specs U2 and U8 are still good. So for these 2 parts I found at Digi-key :

...And am I correct that my old AMC1117's are positive adjustable voltage regulators ?
Question now is do you see anything else I should test before ordering , or would you say its time to replace and re-test ?

[PlainBill]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...voltage regulators

Very good Bill, many of us need a mentor like you so we can then 'do the math'.. thanks for the explanation.
So then these LDO voltage regulators do play a key role in the system start-up and no doubt also control the back lights, and other functions. Without a good schematic I see what your saying its hard to know what is doing what.
That U33 has been a popular failure with Vizio, at least with this series of main boards. And now I agree my U7 is out of whack. I see why U9 is different and OK, and also from the specs U2 and U8 are still good. So for these 2 parts I found at Digi-key :

...And am I correct that my old AMC1117's are positive adjustable voltage regulators ?
Question now is do you see anything else I should test before ordering , or would you say its time to replace and re-test ?

When the output of a voltage regulator is wrong there are a number of questions to be answered.
1. Is the input voltage correct? (In this case, yes)
2. Is there an excessive load on the output, or did the regulator 'die'?
3. Was something damaged by the incorrect output? (In this case, unlikely).

You can get a partial answer to question 2 by rigging up a test circuit. Hook a 9V battery from Vin (+) to Gnd (-). Measure the voltage at Vout. If it is not 1.25V, the regulator is bad. It could still be bad even if the output reads 1.25V; you weren't putting any load on it.

The LM1117 is a positive adjustable voltage regulator.

PlainBill

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...U7 and U33 test

This test was not easy to do, had to make another set of needle test leads and enlist an aide to help hold all the contacts. With the set power disconnected but not the board, a 9V battery held across the fet pins 1 and 3, I read 0.55V out on U7, but just a budge like 0.03V out on U33.

[PlainBill]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...U7 and U33 test

This test was not easy to do, had to make another set of needle test leads and enlist an aide to help hold all the contacts. With the set power disconnected but not the board, a 9V battery held across the fet pins 1 and 3, I read 0.55V out on U7, but just a budge like 0.03V out on U33.

You're going to hate this response. It's best to do this test with the IC removed from the board. Otherwise you are trying to power whatever requires that voltage.

PlainBill

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...take 'em out !

Hate...well yes and no...I had already consigned to the fact I didn't like the availability and price on the mainboard, and already bought the 2 inverter boards, so was getting ready for your next step in taking this one apart. In fact I found I had a pair of these type IC's . I will desolder the 2 in question and re-test, but since they are like 75 cent units, would have been putting a new ones back anyway.

While we're waiting for the 'new' test numbers, do you think these digikey voltage regulators...>http://search.digikey.com/scripts/Dk...P1117EGDICT-ND
...will work ok in place of the oem AMC1117 ?
Or would these be better required ....>?http://search.digikey.com/scripts/Dk...=497-1229-1-ND
My concern is the input voltage rating of the AP1117E I have on hand is 6.4V-18V, where as the circuit runs at 3.5-5.0 ...is this a problem ?

[PlainBill]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...take 'em out !

Hate...well yes and no...I had already consigned to the fact I didn't like the availability and price on the mainboard, and already bought the 2 inverter boards, so was getting ready for your next step in taking this one apart. In fact I found I had a pair of these type IC's . I will desolder the 2 in question and re-test, but since they are like 75 cent units, would have been putting a new ones back anyway.

While we're waiting for the 'new' test numbers, do you think these digikey voltage regulators...>http://search.digikey.com/scripts/Dk...P1117EGDICT-ND
...will work ok in place of the oem AMC1117 ?
Or would these be better required ....>?http://search.digikey.com/scripts/Dk...=497-1229-1-ND
My concern is the input voltage rating of the AP1117E I have on hand is 6.4V-18V, where as the circuit runs at 3.5-5.0 ...is this a problem ?

The parameter you are interested in is the Dropout voltage - how low the input voltage can go before the output voltage of the regulator drops. The second one has a marginally better dropout voltage AND a wider range on the input voltage.

PlainBill

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...LDO reg's out

First time with Chip-Quik......will recommend it to all you 'heavy metal' types !

Not sure I got the right reading...here's what I did, hooked my 9v to the 1(-) and 3(+) pins, then my meter positive to the Vout pin 2, and negative to battery ground or pin 1, and read 7.5 V on both U33 and U7 chips . My battery reads 8.7V right now. Is this the right way, can't see any other way to read Vout.?

BTW, had to remove the caps C18 and C27 to do the work, and they read 0.35 ESR and 215uf (25V)...too high for me...previously they had read 0.10 and 0.07 in circuit, and appear to be a close part of the regulators loop. Guess I should take out all the caps near these voltage regulators before closing the deal.

Fixed my camera...look hand helds..>

[Dgtech]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...

Something is not right. The datasheet for this AMC1117 shows that it is - "Three-terminal adjustable or fixed 1.5V, 1.8V, 2.5V, 3.3V, 5.0V outputs".

Also, there is a chart on page 3 that shows the input voltage maximum is only 7Vdc for this chip. To do a proper test on this you may need to trim that voltage down a hair to test out the regulator - bring the 8.7VDC down to 6 - 7 Vdc .

I recently had one I wanted to test so I had one meter on the input voltage and one on the output voltage. I would then adjust the input voltage to monitor the range of the regulator and to make sure it drops out when it should.

[kingofcoins]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...

Sorry DG my page 3 says recommended operating input is 2.7 to 12VDC:

[Dgtech]

Re: Vizio VW42LFHDTV10...Brother Mikes TV...

Ok that was odd. I found a data sheet earlier that said otherwise but you are correct. I must have looked up a different version of this chip.