Viewsonic VG920 2 seconds...

[SBlackfoot]

While waiting for a regulator for my Proview I decided to take apart my Viewsonic with the usual two seconds to black issue. Now that my regulator has arrived, I'd like to get this Viewsonic off of my work table.

It's a Viewsonic VG920 with the usual problem. I looked it over and saw no evidence of bad components that I could find. The caps all looked normal physically, the transformers don't show an open circuit and are pretty close in resistance to eachother (once I figured out the pinout, they're sideways!). A few of the caps were Rubycon which surprised me.

I replaced all of the small caps and only the larger non-Rubycon ones (not including the big one) since my stock was getting low, no change in behaviour. I picked up some more caps tonight so I can replace the three Ruby's if need be.

What strikes me as odd though: I have a spare CCFL with two longer lamps from an Acer. If I hook only one of the lamps to either of the top two connectors, only about 3/4s of the tube lights up. Are they a matched set? If I hook up both tubes they both light up end to end, but only about half as bright as they should be. Hooked up to the bottom two connectors the Acer tubes light up nice and bright. No matter the combination they still shut off after two seconds. At this point I'm at a loss. Any suggestions?

[budm]

Re: Viewsonic VG920 2 seconds...

Since both transformers are driven by the same set of output transistors, that will eliminate the inverter primary drive circuits, this will point the problem to be either bad transformer or bad ballast caps (small blue caps by the lamp connectors).
I would swap the transformer to see if the problem will follow from the top to bottom (bottom outputs are OK per your test) output. Check or swap the ballast caps or measure for leakage resistance and check the value.

[retiredcaps]

Re: Viewsonic VG920 2 seconds...

1) 2 seconds to black can be (regulars may skip 1, 2 and 3).

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

2) More details starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

3) Also, see budm's Inverter tester using old CFL

https://www.badcaps.net/forum/showthread.php?t=19987

4) What are the exact ohms readings on your inverter transformer? We have had a number of people mis-interpret their multimeter readings/results in the last 96 hours so now I prefer to see the actual readings. "Pretty close" can mean a lot of things to different people.

[SBlackfoot]

Re: Viewsonic VG920 2 seconds...

While still soldered to the board, the top transformer gets on it's windings:
output side: 2.38k ohm
input side: 449 ohm, 1.2 ohm

And on the bottom I get:
output side: 2.32k ohm
input side: 449 ohm, 1.2 ohm

In my mind that's fairly close but I am the rookie in the room. I can edit the pics to show where I tested if it helps. How would I go about checking the balast caps?

[budm]

Re: Viewsonic VG920 2 seconds...

Set the meter to the highest scale and see if the cap shows any reistance reading, cap is an open circuit component. Or just swap the caps.
Did the problem move when you swap the transformers?

[SBlackfoot]

Re: Viewsonic VG920 2 seconds...

Sorry abot the delay, I'm not as confident in my soldering skills as you guys. Removing parts, no problem. Removing without cooking 'em, that I'm not so sure about. lol

On my 2000k ohm scale all four ballast caps show open circuits. I then swapped the transformers (wow that little suction pen worked good!) and the dimmer lamps did indeed follow the transformer, now it's the bottom set that aren't very bright.

So logically, replace the transformer. I do get a slight whine out of the board though when it is plugged in, which gets a little quieter when it's turned on and louder when off. Is it possible that those two transformers aren't being supplied with enough power? There are still three old Rubycon caps onboard... Just grasping at straws, I was hoping to get this thing off of my bench soon.

[Toasty]

Re: Viewsonic VG920 2 seconds...

Same PSU/Inverter as Dell E176FP, Acer AL1716BD or AL1916, Lenovo(IBM) L171, ad nauseum.

Service manual attached.

Post numbers on transformers for research please.

Several working boards currently on eBay for $25 BIN, China, free ship. Also $17.99 auction, USA, in 4 days.

715G1492-1 or 715G1492-2

T

[budm]

Re: Viewsonic VG920 2 seconds...

You may want to replace both transformers at the same time, and also a new set of caps so your monitor will last for more years to come, the only thing that may go/worn out in the future will more likely to be the lamps.
By the way, I always add more solder before I remove the solder with the solder sucker.
Also check that gray rectangular tuning cap sitting between the inverter transistors, that is one part that commonly fails and it will take out the inverter transistors if its value changed or has leakage resistance.

[SBlackfoot]

Re: Viewsonic VG920 2 seconds...

Yeah I did the add-more-solder trick too, it seems necessary to get the old solder flowing. I had way more success this time than the last time I tried. It seems to be a lot tougher when the leads sticking through the board are folded over instead of sticking straight through.

The number on the transformer looks like 80GL17T-28-DN. It's awfully tough to read it's so small.

[Toasty]

Re: Viewsonic VG920 2 seconds...

Okay. I found the trafo on some Chinese sites. Low price (<$3), but the shipping ($15) makes it not worth it.

http://taobaogateway.com/product/12775634442

Why not get the eBay board and transfer your new caps to it? You'll end up with a spare transformer too.

T

[SBlackfoot]

Re: Viewsonic VG920 2 seconds...

I think I'll have to keep an eye out for a spare on eBay or something. It's just a 19" monitor, it's really not worth it for me to sink any significant money into it.

[Toasty]

Re: Viewsonic VG920 2 seconds...

??

[SBlackfoot]

Re: Viewsonic VG920 2 seconds...

Just thinking that it's probably not worth it to spend $25 on a panel that I could probably replace outright on Kijiji for $30. I mean, I'd love to get it working but if it just doesn't add up...

Do the transformers need to be a specific pair, or will any matching pair do? Wondering if I could salvage transformers from a totally different board just to play around. Do my old ones look totally out of spec? They still seem fairly close in range to each other to me, and I didn't see any open circuits.

[jetadm123]

Re: Viewsonic VG920 2 seconds...

Unfortunately, you can't use a transformer from just any board, since the circuit is designed specifically for the specs of that transformer(s).

[Toasty]

Re: Viewsonic VG920 2 seconds...

"Do my old ones look totally out of spec? They still seem fairly close in range to each other to me, and I didn't see any open circuits."

Remember that you are dealing with AC, not DC, when it comes to transformers.

Unless there is a significant difference between the readings, resistance checks do little more than confirm continuity of the windings. A ringing test is the only way to be certain. One winding shorted to an adjacent one will not show any resistance difference, but will definitely cause the symptoms you have.

You proved it is the transformer when you moved it and the problem followed it.

T

[Recycler]

Re: Viewsonic VG920 2 seconds...

Just wanted to add my experience with this inverter board, the same one as posted but found in Acer AL1706ab.

The board looked perfectly fine, no bulged caps.
But turning it over to observe the solder side, underneath one of the inverter transformers there was a big burned spot.

Measuring the secondary winding of that transformer: It resulted to be open.
I opted to buy the complete board on Ebay for 20 USD because the transformer itself could not be found (maybe in China but to expensive due to shipping)
The transformer part no. is 80gl17t-28-dn.

Cheers.