Raising a Viewsonic vp171b from the dead: In the event others find this useful

[xiphmont]

My home [work] machine has three matching flatpanels I bought years ago when they were the beat-all high-end model (Viewsonic VP171b) and relatively expensive. A few days ago after a messy power hit, one of them started squealing and refusing to power on cleanly, but it still worked after a few tries. Yesterday, it died completely.

There were several identical-looking but internally different versions that all used the same model number; you can still get some parts for the later versions, but mine was the original and it's been discontinued long enough that Viewsonic no longer offers any service parts. Googling around, it's apparent my problem is endemic to the model and it's surprising the monitor lasted as long as it did.

Symptoms:

1. While the monitor still apparently works perfectly and before showing any other symptoms, it makes a faint 'beeping' when powered on but sleeping. The monitor that failed had done this for years.
2. Eventually it starts making faint switching regulator noise when displaying; the noise often shifts when the image on the display changes.
3. Eventually (after five years in my case) it stops powering on cleanly; there's a long delay before the backlinght fires, or the backlight cycles several times before staying on. The monitor may 'crash to white', an effect not unlike film getting stuck in a movie projector and melting.
4. In the end, it simply flickers/cycles the power light endlessly without ever lighting up.

Like I said, I have three of these. It always struck me as odd that one of the monitors 'beeped' when it was asleep and the others were quiet. It was just loud enough to bug me at night. It sounded like a switching regulator with a noisy coil being intermittently loaded, and I didn't think much of it. Until the blasted thing died that is.

A stressed or old coil in a switching regulator will 'sing'. A strained capacitor will do the same (although by the time you hear an electrolytic capacitor making noise, it's likely ready to explode). A bad cap that is making a regulator work harder can also stress a coil into making noise.

In most modern electronics, the caps go first. Cheap Chinese capacitors [often counterfeits of other brands] exacerbate the problem. I decided to go with the theory that a cap failed-- the symptoms of slow decay fit-- and give a go at extraction. The monitor was already dead. I couldn't buy parts for it, I couldn't send it in for service and I couldn't even replace it with an identical model. Tearing into its mainboard with cutters and a soldering iron wasn't going to lose me anything.

Swapping modules with one of the still-good panels confirmed the mainboard was to blame. The mainboard of the VP171 has a switching regulator on it and several large storage caps. The easiest to get to, by far, was the main storage cap for the board and it had brown goop on it that looked like an electrolyte leak. I replaced it. This changed nothing; the brown goop was apparently just an unsightlier-than-usual adhesive for fastening the cap to the circuit board.

Careful visual inspection revealed nothing out of the ordinary. None of the caps showed any of the usual obvious signs of distress (leaking, bulging, sitting oddly askance from pushing out the cap plug). At this point it seemed less likely a cap was the problem and I nearly did not proceed. The big 2200uF one I replaced tested well within spec after extraction and the circuit board was annoyingly constructed for hand soldering work (multilayer, expansive power/ground planes, miniature through holes and *no thermals*) but I didn't have any better ideas. I extracted power capacitors one by one, careful not to accidentally lift traces despite needing a 100W iron to melt the solder, starting near the power socket and regulator and working out. The first four tested good after extraction. The fifth, nominally 120uF @ 16v was out of spec by an order of magnitude measuring 19uF with a tan delta of 1.4! In retrospect, this was the capacitor I should have looked at first; it was sitting in the heart of the secondary regulator that also feeds the backlight. Suspiciously, the silkscreen on the PCB for this capacitor is oversized; the silkscreens for all other caps on the board match their sizes correctly. Was this capacitor a last minute downgrade from the original design?

The bad cap looks perfect. There is no external indication it failed. For recordkeeping purposes, it is marked TAICON 0310(M) 120uF 16v 105C(HD). The shrinkwrap on the can is dark green. Taicon does not list the HD line on its website, but the '105C' typically indicates heavy-duty [lifetime is specced at 105 Celsius rather than the usual 85 Celsius], and 'M' indicates miniature. I replaced it with a general purpose (Jamicon SK) 25v 200uF cap as that was the closest/bigger match I had handy. The monitor is back together and working properly. It now makes no switching noise when running or sleeping.

Comments

[flaggday.livejournal.com]

Monty, you're like magic!

[scjody.livejournal.com]

My VP191b (which probably has the same mainboard given they're the same resolution) has been 'beeping' when suspended for about a year. I'll know what to do if it breaks, thanks :)

[xiphmont.livejournal.com]

BTW, an update from the next several years of use....

It looks like virtually all of the electrolytics on the main board are counterfeits or just outright defective. They continued failing one by one (usually causing smearing on the screen). Eventually I just replaced them all. The problem's been solved for good for a few years now.

(oh, and greetings /g/)

viewsonic vp171b

[(Anonymous)]

After 9 years of heavy use my vp171b monitor started to show some smears if white on black, usually only after the cold start, slowly self-healing. After a few weeks it became unbearable and screen became really fuzzy and annoying. You advise exchanging "main board capacitors". There are three printed boards, two looking professionally done and one being a product of a cottage industry or worse. The cheap one is, let's call it, a power supply. My monitor always powered up instantly and never made any noise. Do you suggest changing the capacitors a) in this board or b)the gazillion caps in the "center board" or, c) on all other two boards, the HV one as well. Sincerely, ntms@magma.ca

Re: viewsonic vp171b

[xiphmont.livejournal.com]

> After 9 years of heavy use my vp171b monitor started to show some smears,
> starting with white letters on black, usually only after the cold start,
> slowly self-healing. After a few weeks it became unbearable and screen
> became really fuzzy and annoying.

Yup, exactly what I saw when mine started going for real.

> You advise exchanging "main board capacitors". There are three printed
> boards, two looking professionally done and one being a product of a cottage
> industry or worse.

Ha ha, power supply boards always tend to look 'cottage industry'
since they have to be made of much heavier components on beefier
boards.

> The cheap one is, let's call it, a power supply.

Yup, not cheap, just very different looking. I've never had any
trouble with any of the PSU boards.

> My monitor always powered up instantly and never made any noise. My nose
> doesn't see a culprit in the power supply but with electrolytes one never
> knows.

The electrolytics that fail are on the resampler board. They don't
visibly burst or make any mess, they just go bad. I couldn't see any problem until I pulled them one by one and put them on a tester.

> Do you suggest changing the capacitors
> a) in this board or
> b)the gazillion caps in the "center board" or,
> c) on all other two boards, the HV one as well.

I've not had either the inverter or PSU board caps degrade. The
culprit caps in my three monitors were all on the central resampler
board.

Since yours are 9 years old, you're probably going to have to replace
the backlight tubes soon too :-| The inverters on these are pretty
beefy, so when the backlight finally goes, it's the tube wearing out
not the inverter.