Fixed a ViewSonic N3260w

[Toasty]

Re: Fixed a ViewSonic N3260w

Not to dispute you as you have it in hand but that would be the oddest reflection...

[byacey]

Re: Fixed a ViewSonic N3260w

Double Post.

[byacey]

Re: Fixed a ViewSonic N3260w

I checked the National 78L15 datasheet, and it appears it only needs a 2.5V differential to maintain regulation. Maximum current is 150ma, but I doubt the SM transistor is passing that kind of current.

[budm]

Re: Fixed a ViewSonic N3260w

I would have thought so, but it comes down to which one is cheaper.

[byacey]

Re: Fixed a ViewSonic N3260w

I may have some of the low drop out regs in the bin; I'll have to check. If not, I've got 2N4401 transistors and 1W zeners.

I just the thought the reg would be a more elegant solution.

[budm]

Re: Fixed a ViewSonic N3260w

The 78xx needs about 5V min diff (in-out) for good regulation, we only have just about 5V so it will be on the border line, unless you can get LDO version instead.

[byacey]

Re: Fixed a ViewSonic N3260w

if the Zener is 15V, then the output at the Emitter should be about 0.6v less due Vbe drops than the Base voltage (15V). So did you check Q7 and ZD4 which are commonly failed parts. So 14.2 - 0.6 = 13.6V but you are only getting 11.35V, that is not right at all.

I did check ZD4, as I mentioned I measured 14.2V across it. As well the transistor is shot, because the base-emitter voltage is way beyond 0.6V.

I didn't bother removing it to test outside of the circuit. I'm confident with the voltage readings that the transistor is finished.

[byacey]

Re: Fixed a ViewSonic N3260w

C16 is OK, it must be a reflection you are seeing.

I'll take some bottom pics after I get it running and clean up the flux.

I'll replace the remaining primary side caps, but for now they appear and test OK.

Any recommendations on an ESR meter? I should probably get one if I'm going to be working on these finicky supplies.

[budm]

Re: Fixed a ViewSonic N3260w

if the Zener is 15V, then the output at the Emitter should be about 0.6v less due Vbe drops than the Base voltage (15V). So did you check Q7 and ZD4 which are commonly failed parts. So 14.2 - 0.6 = 13.6V but you are only getting 11.35V, that is not right at all.

[byacey]

Re: Fixed a ViewSonic N3260w

Vcc on the PFC chip (IC3) is 11.2V, fluctuating slightly with the pulses.

I measure 36mV across R17 for about 3 seconds, and then it drops to about 24mV for a split second, and then climbs back up to 36mV repeatedly.

J13 which supplies Vs on pin 12, IC1, has 11.0V, pretty steady.

Gate of Q3 is pulsing from .1V to 2.3V

J14 (pin 1, IC3) has 1.3 to 1.7V, pulsing.

In reading about the PFC, IC1, It requires about 12.3V for the VCC voltage to operate normally. Because this is sitting at 11.2V, just below the threshold, I believe this is the cause of the pulsing. The source for the VCC is via Q7 and ZD4, which should yield about 14.4V on the emitter of Q7 if the zener is 15V. I measure 14.2V across the zener; emitter of Q7 measures at 11.35v, collector has 20.5v, base 14.2.

Looks like another case of the 15V supply failure, both the zener and transistor. I'll replace them tomorrow and report back. If I have a 78L15 regulator, I'll put that in, instead of the transistor and zener.

[Toasty]

Re: Fixed a ViewSonic N3260w

Yeah, those little CapXon's are known problem children. An ESR meter will weed them out. Simpler to just replace them with FC, FM, FR, HE or PW series.

I am concerned about C16 as there appears to be a circular fracture on the one end. Understand that those caps are dipped when manufactured. There are no mold or parting lines and that crack indicates an issue.

Great top pics, a few of the bottom in that quality would be super!

T

Note: I adjusted the pics so they are 2000 px wide and attached them here. Photobucket has a nasty habit of deleting pics after a time and it would be a shame to lose them. The next person to come along would have no references to look at. I also have the originals saved personally.

.

[budm]

Re: Fixed a ViewSonic N3260w

Per SCH as post in post21, check the VCC voltage for IC3, check the PFC Diode D7, D8, C34.

[byacey]

Re: Fixed a ViewSonic N3260w

Here's some pics of the board:

http://smg.photobucket.com/user/byac...4e62a.jpg.html

http://smg.photobucket.com/user/byac...3f239.jpg.html

http://smg.photobucket.com/user/byac...2f60f.jpg.html

http://smg.photobucket.com/user/byac...6b449.jpg.html

[byacey]

Re: Fixed a ViewSonic N3260w

No go on the mains filter cap; didn't make any difference. I also tested C16, the blue cap that drives the xfrmr, and it measures .0226uf, as it should be.

Additionally, I swapped out the 1000uF/35V filter caps that I mentioned before with some low ESR ones I picked up today, but no difference.

Looks like I'm going to have to get out the scope and see what IC3 is doing.

[byacey]

Re: Fixed a ViewSonic N3260w

R67 is a 0.51 ohm , and R36 is a 75K; well within tolerance.

I found a 200uF/450V cap in my bins; I'll try and parallel this across the input filter C1 and see if this makes a difference.

[Toasty]

Re: Fixed a ViewSonic N3260w

Yeah, that really sounds like a PFC issue or a weak/failed component in that circuit. It tries to come up and gets shutdown, rinse-repeat.

Cart before horse: The bouncing from 202v to 293v is not because of the supply pulsing, its the problem with the start-up/PFC.

>>R36 measures 74K in circuit, and R67 measures 0.5 ohm in circuit.<<
Are those correct values according to markings?

PW's are fine. It's not -always- advisable to get super-low ESR caps for PSU use as they can cause issues also. Middle-low is perfect. I've had FM/FR cause problems where FC & PW have no problem. PW & FC are very close in most specs.

Can we get some clear pics of your board? There are likely subtle differences.

T

[byacey]

Re: Fixed a ViewSonic N3260w

I don't have an analog meter at home, I can pick one up later at the shop and re-measure the fluctuating voltages. All measurements taken with a Fluke 87.

Standby +5V is good, measures 5.07V and rock steady. R36 measures 74K in circuit, and R67 measures 0.5 ohm in circuit.

The rectified mains voltage across C1 is 165V @ standby. When switched on, it bounces around between 202V and 293V due to the supply pulsing.

Similar situation with the 12V supply, bounces between 8.9V and 11.1V.

The 5V supply is solid when switched on.

24V supply is pulsing as well, 21V to 23.2V.

I replaced the secondary filter caps with whatever low ESR caps I could get from Newark:
1000UF, 35V NICHICON - PW Series - I'm not sure about the ESR on these; I have some suspicions regarding them.
1500UF, 16V,RUBYCON - ZLH Series
820UF, 20%, 25V PANASONIC - FM Series
270UF, 35V Panasonic FR Series
220UF, 25V, Panasonic FC Series

What is the recommended series regarding longevity / high temp and low esr?

I'll find a large electrolytic that I can parallel across C1. I'll also bring home my cap meter and test C16.

[Toasty]

Re: Fixed a ViewSonic N3260w

Welcome!

What caps did you use? Brand, series?

Standby and On voltage readings from PSU? Analog meter is better here than a DMM.

Voltage across mains cap at standby and on also, please.

Sounds like a PFC issue.

1) Use the correct caps on the primary and secondary sides. Low ESR.
2) Check the values of the large (pink) resistors in the pic in post 23.
3) On the back side, inspect all SMDs for burn marks or bubbles. A bright light and a jeweler's loupe are recommended. Clean up any flux residue on the SMDs so you can see the markings clearly. Surfaces should be shiny all the way across devices. If you see a clouded line transecting the device, that's a problem.
4) Check the value and/or replace the large light blue poly cap in the middle of the pic in post 23. It provides the drive to the secondary transformer (to its left).
5) Check the value of the mains cap. Sub another of matching or higher voltage and value. You can usually just tack-solder another across it. Mind the polarity.

T

[byacey]

Re: Fixed a ViewSonic N3260w

Sorry to resurrect an old thread, but I have a FSP212-3F01 that turns on, and I get a picture, but I can see the power supply is pulsing dropping out and re-starting over and over causing the picture to flicker. I've replaced all the secondary caps. I tried replacing the primary side caps, although I just had ordinary electrolytics, not the low esr. When I replaced these the back light was flickering, but no video, so I put the old caps back one at a time, and testing the supply after replacing each cap..

After replacing the 2.2uf, the video came back, but the supply is still pulsing. Any thoughts on this?

[budm]

Re: Fixed a ViewSonic N3260w

OK, we need to fix the 5VSTBY first. Check or replace start-up/running cap C22, C33 (33UF/35V), make sure R65 (5.1 Ohms is OK). Zener Diode ZD4 (15V) is really 15V (I just fixed one last week, the Diode mode test OK but it becomes 10V Zener instead of 15V). You will need variable power supply and a 1K resistor to test the voltage of ZD4.