Viewsonic VT2430 fluctuating 5V rail

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Unplugged the lvds cable and I still hear the throb in the speakers and the 5v rail goes from 4.8V to 5.2V back to 4.8V back to 5.2V constantly like a tic tac and the blue led is shimmering as if it doesn't like something!

I thought of something R_J, tell me what you think. In the schematics there is a line called 5Vamp which I think is the one at fault. If I trace in the schematic everywhere this trace passes and test all electrolytic capacitors along the way (by pulling them out and verifying them with my ESR tester) do you think that could be useful, that I might hit the bad one if it is a capacitor doing this?

[R_J]

Re: Viewsonic VT2430 fluctuating 5V rail

If you think its on the 5VAMP line, try disconnecting it by removing L123 and L101 looks like that line feeds the audio section only.
Does the voltage for the opto in the power supply also fluctuate, did you check C827? or you could tack a regular 4.7 or 10µf across it to see if it stabilizes the supply.

[Davi.p]

Re: Viewsonic VT2430 fluctuating 5V rail

Hi, let play the tv for about 5 mins, touch C108 and if it's warmer than c101/110 then change it, it can go short very rapidly, tell me its brand.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

R_J: I gues I misinterpreted what 5vamp means, I thought it was the 5V power to the board, but if it feeds only the audio section, then my idea of tracing it and check those caps is no good. I'll check the voltage on the opto, that is the TLP621 right? I'll take those readings and report back. I will then remove the board to get to C827 and experiment as you suggest.

Davi.p: Hi Davi.P, thanks for following this thread! You might have missed in in a previous post, but C108 I changed for a Panasonic low ESR cap, along with C101 and 110. I will try however what you say (see if it gets warmer) and report back.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

R_J: The voltage fluctuates on the opto and has the same pattern as the 5V rail as follows: pin 1 from 4.5V to 4.7V, pin 2 no fluctuating at 3.6V, pin 3 from -75V to -77V and pin 4 from -74V to -76V. Off to check C827..........

Davi.p: C108 after 5 minutes being on is at 31C, so is C101 and C110.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok, so I checked C827 and I get a solid 12.5uf @ .37 ESR, so I guess this is not the culprit. I checked it with 3 different testers I have and get values from 10.4 to 12.8 uf (one of my testers is a Fluke so doesn't give ESR). R_J, a question...since we did the load test with the resistors and the 5V rail was not fluctuating, doesn't that rule out the power supply for the problem?

Well, I'm ready to test anything else you think could help us nail this thing down! Thank you so much for racking your brains on my problem!

[vinceroger69]

Re: Viewsonic VT2430 fluctuating 5V rail

have you done the test in post 22? it may rule out the psu and prove its a audio section fault

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Hey Vinceroger, thanks for chipping in! Ok, ready to do the test in post #22, but what is amazing, I can't find L101!! I can see L123 alright, and I see L101 printed on the board, but where is it?

Attached are pics of top and bottom of the board. Can you point it out if you see it?

Tks!

[vinceroger69]

Re: Viewsonic VT2430 fluctuating 5V rail

my guess its the coil/black top device to the left of the l123

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

my guess its the coil/black top device to the left of the l123

But isn't that L102? L101 seems to be the screw hole, but that is ground, so I am a little confused! Unless L101 is in the schematics but not implemented on the board?

Not sure what to do next, should I try with L123 removed and see what happens?

[Davi.p]

Re: Viewsonic VT2430 fluctuating 5V rail

Sorry RDdube, didn't noticed...

[vinceroger69]

Re: Viewsonic VT2430 fluctuating 5V rail

But isn't that L102? L101 seems to be the screw hole, but that is ground, so I am a little confused! Unless L101 is in the schematics but not implemented on the board?

Not sure what to do next, should I try with L123 removed and see what happens?

Sorry was on phone earlier now on laptop and can zoom in better yes l101 does seem too be the screw hole so not sure what too suggest maybe r_j will advise

[budm]

Re: Viewsonic VT2430 fluctuating 5V rail

Do you see that L123 (FERRTE BEADS) that foot print is made to fit two type of inductor: one is for Ferrite beads as installed on your board or they can install ROUND inductor L101 instead, that is why the silkscreen has round shape and rectangular shape sitting inside the round shape.
https://www.badcaps.net/forum/attach...9&d=1532348574

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ah thank the Lord Budm for that explanation, I would have never understood without your input!

Ok, so that means to do the test that R_J suggested i.e. remove the rail for the 5Vamp, I just need to remove L123 and that's it?

Tks again Budm!

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Sorry RDdube, didn't noticed...

Hey please don't be sorry, these threads get longer and longer and you can easily skip some info. If you have any suggestions, I'm open to experimenting!

I should mention that the 5v rail seems to be pulsating rather than fluctuating, as if it was on a timer of some sort. 4.8V to 5.1/5.2V on and off.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Please masters, what would be a next thing to test? Thank you!

[R_J]

Re: Viewsonic VT2430 fluctuating 5V rail

Did you isolate the 5VAMP going to the audio section by removing L123? You never did say if you did or not.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Hi R_J, thanks for your advice. Actually no I didn't yet because I wasn't sure if it was just removing L123 for that test. But now that you confirm it, I will be doing that in the next few hours and report back.

Tks again,

Ray

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok, did the test with L123 removed to disable the audio section, and problem still there, so it's not coming from this circuit. 5V rail still pulses like a heart beat.

[R_J]

Re: Viewsonic VT2430 fluctuating 5V rail

So did that actually disable the audio or did you still here the pulsing from the speakers