Viewsonic VT2430 fluctuating 5V rail

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Took out C322 (which is easy) and I still get a short on it's pads and on the output of I204.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok, I wrote my post the same time as yours will remove L210 immediately and advise.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok, with L210 removed, I no longer have a short on C322, but still do on I204. So I guess it is now time to lift the ground/adj leg of the regulator?

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok, lifted the leg of the voltage regulator, still have the short on the output. What else could it be?

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

All seems to point to D207, because if I measure ohms on C255, I have no short. When I measure D207 in diode mode, one way I get 1.2V, the other way my tester (Fluke 87-V) beeps, which I think could indicate a short? Alhtough it is still in circuit.

[budm]

Re: Viewsonic VT2430 fluctuating 5V rail

D207 which will be connected in series with other component have to be badly shorted out to give 2 Ohms reading, you can check the resistance of D207 to see if it shows low resistance or not, you can also check the Cathode side of the D207 against GND to see if it show low resistance or not.
At this point you removed two filter caps from the output but the low resistance is still present, just have to look at the trace to see where else the output trace goes to. I will have to look at the schematic of the main board to see what the 3.3V is fed to, hopefully the schematic will match your board.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok Budm, I will wait for you advice. Up to now the schematic has been pretty accurate so I do think it matches my board. I will check what you say in the previous post on D207.

[budm]

Re: Viewsonic VT2430 fluctuating 5V rail

The 3.3V output Voltage is named 'DTV-VDD33' 3.3V DTV Demodulator goes directly to many places per schematic.

1) I203 (LM809, Sch PDF page 69)
2) c218 ~ c224 (Sch PDF page 69), one of these caps may be shorted out.
3) IC202 pin 15, 27, 41, 60, 75 (Sch PDF page 69)
4) L204 (Sch PDF page 69)
5) D207 anode (Sch PDF page 69). I doubt that it will be bad diode.

I would try lifting L204

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Ok, L204 lifted, short still there at regulator. Checked C218, pin to pin is short before L204 and after removal of 204.

Also checked D207 diode for resistance and I get .875K ohms....cathode to ground is in the mega ohms, so seems good.

Will do more tests on the other components.....should I be replacing the ones I took out already, as I'm afraid to lose control ?

[R_J]

Re: Viewsonic VT2430 fluctuating 5V rail

I see you are getting it tracked down, there must have been something other than the fluctuating led that was'nt working with dtv-vdd33 shorted. Was the tuner even working or did you just use this as a monitor?

[budm]

Re: Viewsonic VT2430 fluctuating 5V rail

You can put those inductors back in places since we know that the shorts is in the input side of the inductors.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

RJ: Yes and no, please see below what I've found.

Budm: I went on to remove C218 and lo and behold, the shorts had gone! Measured C218 by itself and it was not shorted? So I inspected the underboard pad, copy attached. This is the positive pad of C218, and the arrow points to ground which is a few millimeters from the positive side of C218.

Now C218, I had removed and checked it's ESR (one of the Lelon cheap 10uf) and had reinstalled it and I guess I created the short without knowing it.

So I need yours or RJ's advice...should I carefully remove that blob of solder and recoat with conformal coating, maybe 2 coats before reinstalling a new C218 (panasonic), and then reassemble everything else checking my progress towards the the finish line.

Even though the short will be gone on I204, I still might have my problem of the strobing Led, but what the heck, I am so thankful of you for being able to find this sucker, because for sure the TV portion would not have worked (although the monitor was powering up fine with that short). Continuing my quest with the help of my friends!!

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Well gentlemen, I think we can call this Eureka! Put everything back together with good panasonic caps (well soldered) and the tv/monitor powers up fine and THERE IS NO MORE 5V rail fluctuation!!

Incdredible work and thanks to all of you for helping me out in this, it was an invaluable learning experience as well. Special thanks to Budm who has an amazing profound knowledge and most incredible, he shares it like a great coach and we just get better and better under his guidance! Budm, I think you should consider coming to coach our Montreal Canadiens, they surely would need someone with management skills like you.

Again, this has been another wonderful journey and am grateful to all, specially Budm. Thank you!

[budm]

Re: Viewsonic VT2430 fluctuating 5V rail

Thanks for the follow-up, I am glad it was not the shorted out IC202.
Don't you just feel good that you are able to fix the problem? Troubleshooting is all about using logic once you understand the basic.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Oh yes I feel very good, but not just because I was able to fix the problem but to see people like you share your knowledge and help neophytes like me learn!

I just tried the TV portion and it works perfectly. I still ordered a set of caps for the power supply that haven't arrived yet, and I'm toying with the idea of leaving it as is, it's working so well! Those Elite brand caps in the power supply bug me, but maybe I should just wait for it to fail or maybe not. What would you do Budm?

[budm]

Re: Viewsonic VT2430 fluctuating 5V rail

I would replace them now so you will not have to deal with them later on.

[R_J]

Re: Viewsonic VT2430 fluctuating 5V rail

Good to here you have it working, so what did you find was the cause of the original problem of the pulsing led and +5?

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Hi R_J, you know what, I was thinking about that and it was probably one of the caps on the main board that I changed (I changed a few at a time and tested), but when I changed C218 I inadvertently created a short on the DTV-VDD33 rail which I think masked my repair.

As soon as I uncovered the short on the C218 pads, it came back perfect. I had changed approx half the caps on the main board and will continue to change them as they are Lelon and Hermei caps which I think are not a good brand. I also ordered a set of caps for the power board which are Elite and Hermei brand and will change those also. TV should be good to last a while after that.

Thank you for asking and thanks again for your help!

[vinceroger69]

Re: Viewsonic VT2430 fluctuating 5V rail

Glad you managed too fix your tv i have learnt a lot from this site over the years as only do repairs as a hobby really but i do struggle reading schematics and folowing separate circuits on the boards so its nice when the likes of budm r_j etc take time to point us and educate us in finding the parts/areas too check.

[rddube]

Re: Viewsonic VT2430 fluctuating 5V rail

Hi vinceroger69, you are so right, this site is the most amazing site on the Web. I have learnt so much from many persons, especially Budm, R_J, Will62 (who doesn't come very often) and even you.

I have come to trust everyone, and up to now, I have also given some counsel to others and it has worked. Too bad however that some users don't report back on their progress and you never hear back from them.

Anyhow, this is an amazing community and hats off to Topcat for creating it - what a vision this man has!