Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

[TechShui]

I'm working on a VO32L HDTV10A

Tested all the the voltage regulators (1117s) and u20 is bad, there is less then 1.25v difference between V Out and ADJ.

So I replaced it but I foolishly knocked off tiny SMD resistor R35 (the resistor between ADJ and V Out). I used too much hot air.

I also knocked off CB18 (cap on V IN)

Is there any way to determine the resistance of R35?

All the other 1117s have 1.8k Ohm resistor between ADJ and V Out, and 1.1k between ADJ and GND.

By comparision, the resistor R36, which is fortunately still intact, and is between ADJ and GND measure about 500 Ohms, just under half of the others.

So would it be very wrong of me to assume R36 is around half of 1.8k Ohms?

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Let me rephrase the question.

My concern is if I put the wrong rating of resistor on R35, it will change the Output of the voltage regulator, since it is adjustable.

Is this actually true? Will I risk damaging the circuit further if I put the wrong resistor?

[budm]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

The resistance ratio will dictate the output voltage. You need to figure some how what the output voltage should be for that circuit. if the voltage is wrong the circuit may not work or gets damage if the voltage is too high. See my calculator.

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Hi budm,

I'm posting a photo so you and anyone else who'd like to help guess the value of the resistor can take a stab at it.

I've edited the photo to include the voltages of u20 that I took before removing the 3-pin voltage regulator and losing the resistor (r35) and cap (cb18).

I'll also write them here:
1 - 0.52v (GND is what the pin is labeled, but this is ADJ, right?)
2 - 2.06v (Output)
3 - 3.25v (Input)

And R36 is 500Ohms

Does this help narrow it down?

EDIT: I have the Service Manual for this TV, but it's only 39 pages, and searching the document for u20, r35, r36 and cb18 yields no results.

[budm]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

The confusing thing is that, the PCB show pin 1 as 'GND' which is typical for fixed LDO Regulator IC. But the board does have two reisistors for setting the output voltage, also you were reding 2.06V at the output but you have indicated that the reading was less than 1.25v, how much exactly? it should be within 3% of 1.25V RATING.
What is the exact numbers as printed on the body of the U20?
Can you check the resistance between pin 1 and Ground plain?

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

What is the exact numbers as printed on the body of the U20?

I'm sure we're dealing with an adjustable volt regulator here. The are no dashes after the number. It's K218 and below that it reads G1117.
I agree that it's strange they labeled the board wrong, but all the VRs I've tested so far have been adjustable, and are labeled the same way (GND label on pin 1)

Can you check the resistance between pin 1 and Ground plain?

Yes, but resistance is out of range (infinity).

you were reding 2.06V at the output but you have indicated that the reading was less than 1.25v, how much exactly?

I made a mistake in my opening post, I wrote that it was bad because there was less than 1.25 difference between ADJ and VOUT. I'm sorry for the confusion what I meant is there was more than 1.25 difference between ADJ and VOUT. The exact differential is 1.58v

2.06 (Vout) - 0.52 (ADJ) = 1.58v

If it were good it should be reading 1.77v right? (ADJ + 1.25)

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

So any suggestions? Are Vizio service manuals always this skimpy?

It's inane that they wouldn't include a parts list for all the components or even a block diagram... But then again this is the same company that classifies their service manuals. :/

Is there hope here?

[mu2]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Hi,

I'm pretty sure that I have a main board for that Vizio.
Can you post the part number on the board just so I can verify that mine is the same? Also, this is for a VO32L FHDTV10A - correct?
My board had a different problem and I'm pretty sure that the regulator and resistor are still in place. I can measure the resistors and post the values.
You might be able to get the cap value from an example circuit in the regulator spec sheets. I don't think there are any markings on the caps.

Mike

[budm]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

There are two versions of the main board in this model number, U20 on this OP board is SOT223, the other version of main board uses TO-252.
If we know the output voltage of this U20 then we can choose the correct size resistors, the cap is morelikely to be 0.1uF MLC CAP.

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Thanks Mike and budm for your help.

The board number for mine is 0171-2272-2634
Below that it reads VO32L VO37L MAIN BD

[mu2]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Well I've got the version that uses the TO-252 in the U-20 position.
The number on the white sticker below and to the left of U-20 on my board is
3632-0602-0150(4I)
Not sure if the resistors are the same for both versions.
If you want me to measure them let me know.

Mike

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Yes, Mike If you can that I would be eternally grateful!!

Im assuming the ratings will be the same, on my board the R36 resistor is 500 Ohms.
If your version has the same rating then chances are even greater that both resistors are the same for mine.

What are your values for R36 and R35 (The R35 is missing from mine)

EDIT: if you have a capacitance meter handy I also need to know the value of CB18 near the input of u20

[mu2]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

The value for R36 on my board measures 50 ohms (not 500) and R35 is 110 ohms.
If I did my math correctly then the output should be 1.81 volts.
Vout=1.25 x (1+R36/R35) or Vout=1.25 x (1+50/110).
It really isn't practical to measure the cap you mentioned but my guess is that it is just a decoupling capacitor with the value of .1 mf as previously mentioned.
Good luck.

Mike

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

100nf is Very small ...if I don't have a replacement can I safely bridge the connection?

[budm]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

You can use through hole ceramic disc cap in place. just make the leads as short as possible.

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Ok, I replaced the resistor with a 110 ohm, and placed a ceramic disk cap.

I replaced u20.

The output voltage I'm getting is 2.25v and the TV still does not power on all I get is an orange Vizio led. The power supply is new, from ShopJimmy, all the voltages check good, I'm getting 5.16 stby.

The service manual once fails to contain any useful information, I've found more useful info in old threads right here on Badcaps

It does seem odd that the output of u20 is slightly higher than what mu2 calculated. However, almost all the other VRs show 2.52v, except for u21 shows 1.25v.

So 2.25 is odd even when compared to the others, that doesn't necesarily mean its incorrect though.

Mu2: I wonder if you'd be kind enough to measure u20

[tom66]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

2.25V is not a standard voltage.

Too low for 2.5V & 3.3V systems.
Too high for 1.8V systems.

[TechShui]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

Yes, I figured as much, so what's the problem? Wrong resistor after all? Slight variance in regulator? Let me post a link to the datasheet hang on

[mu2]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

I only have the pc board and not the entire tv so I can't easily measure the voltage. It was salvaged from a broken screen set.
I concur with tom66, 1.8 volts is a pretty common voltage in a lot of sets including the Vizio's.
I think the regulator on my board is rated at 4 amps and your case style of regulator is less - maybe 1.2 amps or so. Perhaps they made an engineering change with the later version of the board (mine is 4I) because of failures? That's just a guess.
Did you say you have the service info?
I know it's pretty poor for the Vizio's but sometimes they have a trouble shooting diagram with some voltages listed for the regulators.

Mike

[mu2]

Re: Vizio VO32L, another one with bad VRs? Need help figuring out the resistors too

I just went back and re-read your posts. You said the other regulators used a 1.1k.
If your other resistor is 500 ohms then 1.1k in the formula should give you 1.8 volts.

Mike