Re: Vizio VW37L TV - no 5v standby voltage
I did find a faulty Mosfet gate. However, I am unsure as to whether it was an integral component to the initial problem I was having or just another problem in general. That being said, after checking all the suggested components from the previous posts, I am still unable to get the 5v standby voltage.
Also, the voltage on pin 8 of the FA5531 is still bouncing from around 60v to 150v... even after replacing the IC and various resistors. In addition, the voltages on pin #2 and #3 of the IC are no longer yielding a stable voltage,...
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Re: Vizio VW37L TV - no 5v standby voltage
It will be later today before I can fully check the readouts as I am not currently at home, but from memory, it was the 2 outer legs that showed continuity... so the gate and the source.
When measuring from the gate to drain or drain to source, the readings were roughly .5 or 1.9, depending on probe orientation.
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Re: Vizio VW37L TV - no 5v standby voltage
The marking on the mosfet are:
H24
FQPF
3N80C
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Re: Vizio VW37L TV - no 5v standby voltage
I'm not all that knowledgeable on checking the mosfet's in circuit, but with the board disconnected from power, Q905 shows a direct short or connection between two of the legs. A quick check of the other similar mosfets do not yield this result. I am not sure if Q905 is a direct piece of the IC FA5531 circuit, but is this normal for 2 of the legs to show continuity.. or could this be a function of other components in the circuit affecting this reading?
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Re: Vizio VW37L TV - no 5v standby voltage
Dick,
Yes, one leg of C903 shows continuity with pin 6 of the FA5531.
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Re: Vizio VW37L TV - no 5v standby voltage
I replaced the R907 resistor. However, the voltage on one leg of the resistor still fluctuated. Coming from the big capacitor, the voltage was steady and correct. On the other side of the resistor (the side that connects to pin 8 on the IC) had fluctuating voltage. If I removed that leg of R907 from the circuit, the voltage into and out of the resistor was stable. When putting it back in circuit with pin 8, the voltage bounces around.
I found a direct replacement IC online. I replaced the IC, but the voltage on pin 8 still...
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Re: Vizio VW37L TV - no 5v standby voltage
A voltage check of the R907 resistor, using the negative leg of the large capacitor as ground, showed the following:
DC voltage at + leg of large capacitor = 162 v
DC voltage at input side of resistor = 161.7 v
DC voltage at output side of resister = 60v-159v, fluctuating
Looks like I will be replacing that resistor first, before trying to do anything with the IC. As capleaker suggested, even though the resistor measured correctly when removed from the board, it appears to be malfunctioning when...
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Re: Vizio VW37L TV - no 5v standby voltage
I checked the resistor and it measured 99.4 K ohms. According to the color bands, it should be a 100K resistor +/- 5%.
I found a replacement IC online and should have it within a week. At capleaker's suggestion, I will go ahead and replace the 100k resistor.. just to be sure.
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Re: Vizio VW37L TV - no 5v standby voltage
Budm,
I will remove the resistor from the board and check it out.
If it checks good, is it safe to assume the IC is faulty and should be replaced next?
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Re: Vizio VW37L TV - no 5v standby voltage
I replaced start up cap C903. However, there was no change in the output and still no 5v standby power.
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Re: Vizio VW37L TV - no 5v standby voltage
Vdc Measurements of the IC pins with respect to pin 4 yielded the following:
Pin #1 - 0v
Pin #2 - 4.94v
Pin #3 - 8.04v
Pin #5 - 0v
Pin #6 - fluctuated between 10.3v - 11.2v
Pin #7 - 0.02v
Pin #8 - fluctuated between 54v - 159v
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Re: Vizio VW37L TV - no 5v standby voltage
Thanks for the drawing budm, and your patience. The spec sheet lists "VH" as pin #8.. which is the upper right. However, and for whatever reason, I was thinking the sequence of the pins had pin #5 across from pin #1... not pin #8 across from pin #1.
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Re: Vizio VW37L TV - no 5v standby voltage
Ahh! Ok, thanks budm! I think I have it now. That would make pin #1 the lower right corner of the shopjimmy photo. (next to the descriptor for C904).
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Re: Vizio VW37L TV - no 5v standby voltage
cyberhack,
The ones under the largest heat sink at the top of the pic? I will inspect those closer this evening.
Thanks
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Re: Vizio VW37L TV - no 5v standby voltage
I will post a better picture of the IC on my board when I get home this evening, as I am still unsure as to which is pin#1. Out of the 4 corners of the chip, only 2 can possibly be #1, but which one? It will depend on which way the chip is oriented, or which way you are looking at the chip, unless I am still missing something.. which is entirely possible.
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Re: Vizio VW37L TV - no 5v standby voltage
Ok, those are the schematics I found as well.. the FA5331. I was confused by the fact that the block diagram only shows 7 pins, when there are 8 legs on the chip. Which is pin #1, #4, etc? Did I overlook something in the spec sheet that determines orientation? When looking at other similar chipsets, they always seem to have a "dot" or marking referencing pin #1.
From reading other threads, pin #4 should be ground.. which is tied to the negative leg of the large capacitor on the hot side. Would it be as simple as...
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Re: Vizio VW37L TV - no 5v standby voltage
The markings on IC 900 are: 2A07905 and 5531. A search of 5531 comes up as possibly being a Fuji chip? I found a few different data sheets for the 5531, but am still unsure of exactly what I should be checking for on it. Also, should the start-up cap be replaced before checking the IC?
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Re: Vizio VW37L TV - no 5v standby voltage
Capleaker,
Yes, I will have to order it... no local supply stores near me.
I am not familiar with the MIP. Where on the board is it located, or rather what is its function?
Thanks
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Re: Vizio VW37L TV - no 5v standby voltage
Ok. It will take me a couple of days to get a cap. I will replace that and then report back.
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Re: Vizio VW37L TV - no 5v standby voltage
With the Positive probe on the center leg, and the negative on each outer leg, the readings were 8.0 K ohm for each leg.
Reversed, the readings were 0.965K and 0.966K.
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