view sonic VS11838-1M channel up running continuiously

[berzy]

Hey all, I'm kind of a noob here. Need some help with a Model=view sonic VS11838-1M but the tv name is viewsonic N4280p-1M.

TO begin this is a junk tv so no big deal but I need practice and I like to pick at this kinda stuff in my spare time.
So started out as a strange problem that only occurred every few hours where no matter what input you were on the tv would flip to tv channel 2. Like someone was messing with you with a secret remote flipping the channel on you. Then it started to happen more and more frequently and had to be dealt with. At first I tried the easy fix which was unplug the board to the channel buttons...worked for a few days then became much worse. Scrolling channel up every second or two.
I knew this would be require much more work. When I opened the tv back for the second time I noticed 4 capacitors bulged. I replaced those but am still getting odd readings on both boards. Not exactly where but basically I thing there is a part that is dropping/increasing the voltage on the secondary board where the button panel is connected causing the the channel up button to be activated.
Sorry if this has been worked on before, I haven't found much info at all on this model.
there are a lot of wires as you can see in the attached pics. As of now I have steady 5V on everything I have tested. but all 18v wires on secondary are reading 11.34vdc.
Really need help zeroing in on the problem. I know enough to get myself in trouble chatting with some one but I am rusty and not sure I am testing things properly with the multimeter.
Also the power coming out of the wall is good at 119Vac and nothing else is visually wrong with the components as far as I can see.

ps. I have pics available but I'm having trouble uploading them right now.

Thanks

B

[dskall]

Re: view sonic VS11838-1M channel up running continuiously

Need some voltages posted from ps conn. to mainboard.

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

Hey Thanks dskall

I'm still trying to get back into this so I'm not certain on all the terminology but I''ll catch up quick.
I assume ps comm to main board is power source communication with the main board. Which I thought was good when I checked initially.
As of now the fuse and everything going to bridge rectifier is 118-119Vac.
Across the B.rectifier reads 164Vdc in standby, 105v when running and 52v from positive to ground.
Across the large transformer when 2 points on left read between 13-12.5Vac and 4 on the right read 5Vac, 6, 8 and 8 respectively.
2 large white Resistors??? maybe read 23.6 and 17.5.

Not sure if I'm measuring this all correctly but I am reversing the leads and being systematic in my approach. Appreciate any help/suggestions you many have.

[dskall]

Re: view sonic VS11838-1M channel up running continuiously

Hard without some pictures. Need to force power supply on disconnected from mainboard to see if 11.34v comes up.
Need voltages from connector that goes from power supply board to main board. Will need pin#,pin label,Pin voltage in standby, and picture of connector on power supply board.
Format:
Pin# - Pin Label - Pin Voltage standby - Pin voltage when power button pushed
1 - XXXXXXX - XXv - XXXv
2 - XXXXXXX - XXXv - XXXv
3 - XXXXXXX - XXXv - XXXv
4 - etc.
Black lead will be on cover or screws

[SLK001]

Re: view sonic VS11838-1M channel up running continuiously

I suspect that the UP button on the TV is bad. I've had this occur before.

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

thanks SLK001 but that was my initial hope and unplugging the the board with the buttons only fixed the issue temporarily before making it worse and blowing 4 capacitors. I asssume because stressed parts finally gave to the added voltage/amps from unplugging the board.

That being said I hear ya dskall. very difficult to troubleshoot blind. I have plenty of pics to share but I'm restricted for now being new and all. I can send you pics of the boards to start and anything specific after. I'm in no rush just a thing to pick at and practice on.....and what a unit to start with. It seems complex with dozens of wires and multiple boards as I just noticed.


So I have most of the readings you were looking for but wanted to double check them and also see the readings with the channel up/down board unplugged. Just about to start that and noticed another long board down the side with ribbons connected from the main board. Everything looks good visually with the 4 bulged capacitors(35v 2200uF) replaced. I'll grab some new readings and respond back soon.

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

k...heres a bunch of results to think about. All reads will be as if the ribbon was at the top of a board and read left to right.

3 sets of readings done both boards...Standby power, Power on and Power on with channel up/down board unplugged from secondary. The secondary and new board I mentioned that I noticed near the secondary powered by main board.

Secondary board - first ribbon back to main reads:

stby pwr on pwr on/no buttons

9v 8.89 0 8.89
GRD 0 0 -0
5v 5.01 0.02 5.01
GRD 0 0 -0
18v 11.21-11.32 0.3 11.30
18v 11.21-11.32 0.3 11.30
GRD 0 0 -0
GRD 0 0 -0
5vS 5.08 5.11 5.08
18v 0 0 0
STB 4.35 0 4.35

Secondary board - 2nd ribbon back to main reads:

stby pwr on pwr on/no buttons

GND 0 0 -0
BR 0 0.01 0.01
ON 0 3.26 3.25-3.26
VLCD 0 11.05-11.21 11.20

------------------------------------------------------
long board - first ribbon back to main reads:

stby pwr on pwr on/no buttons

BLON 0 3.26 3.25
I_PWM 0 0.01 0
E_PWM 0 -0.01 -0.01
SEL 0 -0.01 -0.01
GND 0 0 0
GND 0 0 0
GND 0 0 0
GND 0 0 0
VBL 0 23.5 23.5
VBL 0 23.5 23.5
VBL 0 23.5 23.5
VBL 0 23.5 23.5
VBL 0 23.5 23.5

long board - 2nd ribbon back to main reads:

stby pwr on pwr on/no buttons

HDRCAL 0 22.3 22.3
LDRCAL 0 1.2 1.2
HDR2A 0 22.3 22.3
LDR2A 0 1.2 1.2
FBK2 0 0.3 0.3
VSEN2 0 1.6 1.6
NC 0 0 0
NC 0 0 0
NC 0 0 0
NC 0 0 0


Phew ....that was longer to type than test...lol
Nothing else to note other than I didn't get any different readings with the button board unplugged and in standby power mode. I did notice that the VBL leads held the voltage when the tv was disconnected from power and the stby light stays on longer now when unplugged. I assume do to a voltage leak somewhere. Hopefully this paints a better picture for people. I'm sure its and easy fix but I can't easily detect it.

Thanks

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

dskall.... I'll get the pin labels and voltages when the power button is pushed shortly.

I assume you mean voltages as the power is activated and during bootup for each lead???

Sorry for the formatting...I did have it spaced out better but changed after upload

[dskall]

Re: view sonic VS11838-1M channel up running continuiously

Need to find out why 11.21v on two 18v line and 0v on one

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

Here are the 2 boards in question. there is another with the standard def and tv tuner on is as well as to the long boards I just noticed today on each side.
As you can see this is a mess unit with plenty of ribbons and boards to look at.

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

Yes that was my first thought was well. Something obviously draggin down those 2 18v and I wasn't sure what the other was used for ....if powered always or when something was in use.

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

Also should mention that I have played around on the secondary board a lot just testing with the multimeter trying to find some inconsistencies in various resistors, diodes, etc. All in circuit of course, I didn't go as far as removing anything to test yet other than the capacitors. Nothing found that stands out as of yet. But i also tried the canned air trick to see if any frosted parts heat up quickly and there was a couple suspect parts but I'm not 100% sure if they are bad or if I'm testing things properly.

[BangBusDriver]

Re: view sonic VS11838-1M channel up running continuiously

I would check for shorts to power/ground on the circuits that lead to the buttons, or on the IC that the buttons likely act as an input for.
I suspect they will lead to the TV's main micro controller, but I could be wrong. I also hypothesize that you could have a problem in the IR sensor circuit causing it to get false readings, might want to check there too.
This is more likely a problem with related to digital or analog logic than your power rails. Also keep in mind that when measuring the voltage on the power board some voltages will be ac, you might have to use the ac mode to get a proper reading.

[BangBusDriver]

Re: view sonic VS11838-1M channel up running continuiously

What you really need to do is find a schematic so that you know what are poking around at. Sometimes they even give correct voltage readings for components.
You might find one in the TV's service manual, or you could look it up by the part numbers on the boards. Each board should have a different part number and it should be pretty obvious when you examine them.

[BangBusDriver]

Re: view sonic VS11838-1M channel up running continuiously

Just to give a through understanding of how these buttons/Remote Control sensor should work, the buttons are just switches. Pretty simple. They have a positive and a negative side. Although I can't tell you exactly what they connect to, eventually, the voltage that passes when you press the button is read by as input by something ,and eventually is turned into digital logic used to change the channel output.
The IR sensor (If you don't have a radio remote or some other tech, but I assume IR since it is an old TV) usually is just a light sensitive resistor that changes resistance based on what is shining on it, thus producing different voltage readings which, possibly in combination with different sets of pulses or IR, allow different button presses to be detected.
So, you are hunting for an issue anywhere along those chains of events. Something is making this channel change trigger falsely, and if your TV is turning and working otherwise, I doubt its an issue with power supply.

[BangBusDriver]

Re: view sonic VS11838-1M channel up running continuiously

Oh, and also, your TV probably has a main board, responsible for creating your picture and all the other logic, a power board that provides power, a TCON that controls timing of the screen, and than probably driver boards (usually long ones, on side or top/bottom) that split the power from the supply across all of the rows and columns, and controls the individual pixels. These driver boards are a bit complicated in that the screen has so many connections for the individual pixels, it is impossible to hook them all to one chip, so the driver boards minimize the number of connections needed, usually through multiplexing. Hopefully some of this information helped.

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

Thanks BangbusDriver
I have been systematic in testing because its tough to identify/test these parts but mostly because I'm just getting back into this and I'm not confident I'm testing things properly or can even test what I need with a basic DMM. I did do a bit of small electronics in school 25 yrs ago so I understand basic stuff about diodes, rectifiers, etc or relays as you mentioned earlier about the IR system. But I only remember enough to not get myself in trouble...haha hopefully.
So I have tested what I know which is the obvious stuff starting with the power input to the power supply and onward. But I don't have professional gear just a decent DMM and I have not found anything on this type of tv model online as of yet to help me break it down.
That aside I've unplugged the the IR board which runs the stby lights and used the button board and tried the reverse as well with the same result. My guess is that I have a burnt out component or several that are causing the 18Vdc on the secondary board to be dropped to 11.3ish. As I mentioned I don't have enough info or know-how to figure out the advanced stuff and follow that this 18v lead is connected down the line to this and ....bippy boppity boop ohh there is a problem, and so on. I don't even know at this point if the issue is on the mainboard messing up the 18v on the secondary or if it originates from the secondary.....or if that is in fact the problem at all. I'm sure a pro has a quick little DMM trick to rule out where the root problem is but I'm not there yet...haha. But that is also the fun in being able to try, test and learn these things. I have another tv but why not spend a few bucks trying to fix this and learn a little in the process.
Back story to all of this is I live in the Arctic and things are not cheap, easy to get/ship nor is it possible to have a service center or technician look at "it". So I have seen many many things go to the landfill because of a fuse...frayed cord....motor burnt out....clock not working type things. And I've had to do a lot of my own repairs and replacements out of necessity. Really funny in a place that is so expensive but there is always more money these dayz than brains....hahaha

sorry for the lenght....thanks for the help gang.

[dick_barton]

Re: view sonic VS11838-1M channel up running continuiously

Is that a burn mark on R523 on the power board or a pen mark?
Also what DC voltage do you have between the two legs of the large capacitor with CD294 on top and what is the voltage rating written on it?

[petehall347]

Re: view sonic VS11838-1M channel up running continuiously

what i would do next is take out the boards and give them a damn good wash in the shower using washing up liquid and brush .. rinse well and dry with airline then wash with iso then airline again then put in warm place for at least a day then see if problem fixed .

[berzy]

Re: view sonic VS11838-1M channel up running continuiously

Sorry for the wait. I've been away from home.

Thanks...Petehall. first thing I do is put al my stuff through the dishwasher. Then I get to work on it....Movin' on.

Dick_Barton.... that is a marker tick that I made. You may see a few around. Just reminders to recheck something if it was inconsistent with the other comparisons I made.

I'm still waiting on parts also, if you notice there is some flux spillout on the 2nd pic in the bottom left corner. I have a variable power supply and a few more things to make my testing a little easier/safer.

I will get back tomorrow after I try a few more things and hopefully have someting new to report.