Bad Viewsonic LCD monitor

[PlainBill]

Re: Bad Viewsonic LCD monitor

I guess that is normal for a monitor that size. I'm using one of those to view this thread (a VP201b like the one of this thread, not a VP211b. I have two units of that model with a broken screen....). My best guess is that your PSU has a problem (due to the fact that you are using external power and so far, so good). I can't remember what caps did my own VP had when I received it, but I replaced them (2 1000uf 25v caps) and it's been like three month of continual (almost) use, and nothing has gone wrong. Have you checked the V output of your PSU, or replaced any caps in there?
What caps do the PSU have?

The PSU output was 17.5 volts. A little below the rated output of 18V, but well within 5%.

I visually checked the caps in the PSU; they are 1000uf Rubycon's (I don't recall the voltage rating). I don't have an ESR meter (yet) and my capacitance meter only goes up to 20 uf. Replacing the caps did cross my mind, but I first wanted to verify the problem wasn't occurring on the logic board.

NOW things are getting even screwier. As an aside, I've been working with electronics for more than 40 years. When I got started radios had tubes! I prefer 'broken' equipment to remain broken until I replace the defective part. As one of my friends said "Equipment that fixes itself will break itself, usually at the most inconvenient time possible".

After replacing the fuse, the shield over the PSU and logic board was replaced and the monitor hooked to a computer running Windows XP. As noted, it failed after half an hour (this happened twice, the second after it was unplugged for more than 12 hours). The test with the replacement power supply was done with the shield off. To verify it was the original power supply I hooked that back up (left the shield off) and let it run for a couple of hours. No problems!! I put the shield back on and again it ran for several hours without problems. On the hottest day of the year. The only variables are the additional run time and the computer it was hooked to.

It IS a bear to get the back off the monitor. I would prefer to get it fixed for SURE before putting the back on again. I hope to have this as my main monitor. Am I right to assume that replacing the two caps in the PSU would be a reasonable precaution?

Thanks,

PlainBill

[EGuevarae]

Re: Bad Viewsonic LCD monitor

"Equipment that fixes itself will break itself, usually at the most inconvenient time possible".

My father used the same phrase (more or less, it was the Spanish version). Pure knowledge.
He was (until 2 years ago) an Electronics technician that saw how the TV went from BW to color, and from tubes to Qs and now ICs and LCD/plasma. Too bad that diabetes had deteriorated him so bad that he can't do it anymore. He would be a great help to me (and others) now.
Rubycons are good caps (post V rating and series if possible), but they can fail too. If you can and have them (or can get them easily), it would be a good idea to change them. then put the shield back on (shield only, not the big bad black cover) and test again. When I fixed mine, I only had caps that were too fat to fit in ther, so I had to put one flat against the board and the other a little above it (legs like 3/4" long) just to test. Then I tested it with the cover because I couldn't fit the shield again, and was using it that way until the replacements arrived and I fixed it with the right ones.

And seeing my notes, my PSU pumps a constant 18.5v

[PlainBill]

Re: Bad Viewsonic LCD monitor

My father used the same phrase (more or less, it was the Spanish version). Pure knowledge.
He was (until 2 years ago) an Electronics technician that saw how the TV went from BW to color, and from tubes to Qs and now ICs and LCD/plasma. Too bad that diabetes had deteriorated him so bad that he can't do it anymore. He would be a great help to me (and others) now.
Rubycons are good caps (post V rating and series if possible), but they can fail too. If you can and have them (or can get them easily), it would be a good idea to change them. then put the shield back on (shield only, not the big bad black cover) and test again. When I fixed mine, I only had caps that were too fat to fit in ther, so I had to put one flat against the board and the other a little above it (legs like 3/4" long) just to test. Then I tested it with the cover because I couldn't fit the shield again, and was using it that way until the replacements arrived and I fixed it with the right ones.

And seeing my notes, my PSU pumps a constant 18.5v

I knew I shouldn't have answered the questions from memory - I don't have any left. After double checking, they are Nichicon 680uf, 25 volt. Other markings are HO249 (or H0249) and PW (M) and of course 105°C.

But the caps are PROBABLY not the culprit. About half an hour after the monitor was hooked up to the first computer it flaked out. After further investigation I found that the 'test bed' had it at 1280 x 1024, while the first computer has it at 1600 x 1200 (which appears to be it's native resolution). I'm going to try the external power supply with the resolution cranked up to 1600 x 1200 for a few hours and see if it makes a difference. If it STILL flakes out that would point to the logic board. All the caps on that are surface mount. Maybe I'll pull out the scope and see what the 5V supply looks like...

Thanks for the advice

PlainBill

[EGuevarae]

Re: Bad Viewsonic LCD monitor

I knew I shouldn't have answered the questions from memory - I don't have any left. After double checking, they are Nichicon 680uf, 25 volt. Other markings are HO249 (or H0249) and PW (M) and of course 105°C.

But the caps are PROBABLY not the culprit. About half an hour after the monitor was hooked up to the first computer it flaked out. After further investigation I found that the 'test bed' had it at 1280 x 1024, while the first computer has it at 1600 x 1200 (which appears to be it's native resolution). I'm going to try the external power supply with the resolution cranked up to 1600 x 1200 for a few hours and see if it makes a difference. If it STILL flakes out that would point to the logic board. All the caps on that are surface mount. Maybe I'll pull out the scope and see what the 5V supply looks like...

Thanks for the advice

PlainBill

If you are sure (after testing) that the logic board is bad, post a pic to see if it is the same as the ones I have here. Maybe I can part a monitor of the two I have here (VP211B).
Let me know.
- Eduardo

[PlainBill]

Re: Bad Viewsonic LCD monitor

If you are sure (after testing) that the logic board is bad, post a pic to see if it is the same as the ones I have here. Maybe I can part a monitor of the two I have here (VP211B).
Let me know.
- Eduardo

Thanks for the offer, but it looks like it's time to replace the power supply caps. I ran it for 6 hours at 1600 x 1200 resolution using the external power supply and it worked perfectly. Hook the internal supply back up and half an hour later it has a black screen. Cycle the AC power and the screen is back to normal.

PlainBill

[EGuevarae]

Re: Bad Viewsonic LCD monitor

Thanks for the offer, but it looks like it's time to replace the power supply caps. I ran it for 6 hours at 1600 x 1200 resolution using the external power supply and it worked perfectly. Hook the internal supply back up and half an hour later it has a black screen. Cycle the AC power and the screen is back to normal.

PlainBill

Well, in that case, I guess the problem has been isolated to the PSU. But if you need the logic to test, or a PSU, I can lend them to you. Just let me know. I do this (repair LCDs) for several reasons, and one of them is to get out as much plastic/mercury/etc from landfills. If I can lend a part and help to get a unit out of the landfill, it is good, to me at least.
Eduardo

[JordanJTW]

Re: Bad Viewsonic LCD monitor

Hello all, this is my first post and I am glad I have found a forum with what seems to be such well informed members,

I realize that this thread is quite old, but I recently was given a viewsonic vp 201b by a friend who had attempted to repair it and given up... He removed the power supply, thinking he would just buy a new one, but never did, so I am completely missing the power supply...

Since I have a use for it in a little hack project I am working on and don't care too much about looks I was hoping I could just use a a standard dc power supply I have laying around as a substitute for the original... I was hoping one of you might be able to guide me as to which pin is ground and which has voltage...

Any help would be greatly appreciated! Thank you!

[FMA1394]

Re: Bad Viewsonic LCD monitor

I know this thread is old, but it's relevant to me now. I found 2 of the viewsonic models mentioned by the OP in a dumpster (had to rescue them, you know how that goes) with *BOTH* versions of the delta power supply mentioned. One had a barely exploded primary cap (400V 150uF) and I looked at the other one and it *looked* fine. But, I noticed it was the exact same model as the other board. So, I'm going to order two new nichions to fix these two monitors. Will post later with results.

Caps were TAICON.

Similarly, as an aside, I've also got a Viewsonic VP2030b with 4 failed caps (3x 180uF 25V on the inverter board and 1x LTEC (prone to fail, but not yet) 400V 150uF, just like the problems with the VP201B).

Up next on my list of things to look at tonight is some 20" samsung with cap problems.

FMA1394

[EGuevarae]

Re: Bad Viewsonic LCD monitor

Similarly, as an aside, I've also got a Viewsonic VP2030b with 4 failed caps (3x 180uF 25V on the inverter board and 1x LTEC (prone to fail, but not yet) 400V 150uF, just like the problems with the VP201B).

Replace them all...

[FMA1394]

Re: Bad Viewsonic LCD monitor

of course!