Dying monitor! Where to start. - Page 1
Forum section: electronics / repair

author: Section8
author_rank: Contributor
timestamp: June 03, 2016, 09:57:29 am
content: So I've got a dying viewsonic monitor that won't turn on in cold conditions. You press the power button and it emits a squeal and shows a picture for a second before shutting off. If I repeat the process several times it eventually latches on, presumably because it has warmed up enough.My question is where do I start with the repair? Presumably I should be checking the voltages out of the power supply and looking for bulging caps.Do the symptoms suggest anything else I should be looking for?Thanks in advance.

author: DimitriP
author_rank: Super Contributor
timestamp: June 03, 2016, 10:25:46 am
content: Replace all the electrolytic caps.

author: jdraughn
author_rank: Regular Contributor
timestamp: June 03, 2016, 11:14:11 am
content: I was going to say, an EKG can monitor heart rate so you know when your dying

author: GreyWoolfe
author_rank: Unknown
timestamp: June 03, 2016, 12:21:12 pm
content: Remember, caps don't have to be bulged to be bad.

author: TiN
author_rank: Super Contributor
timestamp: June 03, 2016, 01:57:21 pm
content: +100 to replace ALL electrolytic capacitors. I hadfixed onefew weeks ago after spending 5 minutes and few caps.

author: wraper
author_rank: Unknown
timestamp: June 03, 2016, 02:05:56 pm
content: Quote from: DimitriP on June 03, 2016, 10:25:46 amExcept big 350-450V one. It is expensive and fails quiet rarely.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 03, 2016, 05:35:22 pm
content: Your monitor either has bloated caps or caps with high ESR. As the monitor warms up, the ESR drops allowing the monitor to come on. For replacement caps, you must use low ESR caps purchased from a reputable distributor (i.e NOT ebay or aliexpress). An example of a low ESR cap is Panasonic FC, FM and/or FR series.

author: TheMG
author_rank: Frequent Contributor
timestamp: June 04, 2016, 03:39:41 pm
content: If this monitor uses CCFL backlighting, it could also be that the CCFL lamps have reached their end-of-life, in which case the backlight inverter switches off after a short time.Easy way to tell if this is what's happening, shine a bright flashlight on the LCD monitor and see if there is still an image displayed on the screen after it shuts off. If yes, then your problem is the backlight. If no, it's probably bad capacitors in the power supply.

author: wraper
author_rank: Unknown
timestamp: June 04, 2016, 04:10:25 pm
content: Quote from: TheMG on June 04, 2016, 03:39:41 pmNo, this not the way at all. By this you can only check if the monitor shuts down completely or backlight only. Dead caps in the PSU will cause the CCFL inverter to shut down exactly the same as the fault in the inverter itself (usually faulty transformer) or CCFLs. The fact that monitor does not start at lower temperatures suggests faulty capacitors. FYI ESR of the electrolytic capacitors rises when lowering the temperature. And when ESR of the faulty caps is just low enough for still being functional, ambient temperature will make the difference between starting or not.

author: Section8
author_rank: Contributor
timestamp: June 08, 2016, 08:07:54 am
content: Thanks all for your help. out of the 10 on the power supply board 5 have a visible bulge and a few even have signs of corrosion/leakage.so, if I said "is it ok to use the low esr ones that Jaycar sell?", would that pass the laugh test? (I appreciate they might not be the best possible brand, but realistically I'd be amazed if I hadn't replaced these monitors within 3 years)

author: Section8
author_rank: Contributor
timestamp: June 08, 2016, 10:27:58 am
content: Quote from: wilfred on June 08, 2016, 08:24:40 amGreat, thanks Wilfred.I might replace all but the big mains side one first, as that one costs as much as the others combined. I work quite close to a jaycar so its not a big deal to go back if I need to. I will get the low ESR ones though.Let yas know how I got on after the weekend.

author: tautech
author_rank: Super Contributor
timestamp: June 08, 2016, 10:58:54 am
content: Just fixed one of mine....for the second time and I'll share some symptoms.First time.Would run for a while and then PSU would shut down and reboot. Rinse and repeat.Had it apart and replaced the SMPS controller PSU cap (low value) and all the 5V rail PSU secondary caps.(low values)Tested all other PSU caps....seemed OK. NO signs of bulging or leakage.Problems still.Second time.(it's some weeks since I've had a chance to get back to it)Same symptoms as before but the runtime before rebooting was longer.Replaced all PSU secondary side caps including 2x 680uF bulk caps close to the backlight inverter.All values tested very slightly low ~5%.!000uF is what I had...they'll do.Of course one should check ESR's to find the culprits but I couldn't be bothered for a few bucks worth of caps.Runtime as I type ~30 minutes.Time to put the covers on and return it to service.EditI should mention that only PSU and backlight inverter caps were replaced.

author: rob77
author_rank: Super Contributor
timestamp: June 08, 2016, 01:32:46 pm
content: Quote from: wraper on June 03, 2016, 02:05:56 pmthey do fail as well, even the good brand ones fail after longer periods of time when operated in higher temperature environments..the other day i repaired a small form factor computer PSU with blown VSB switcher.. replaced the switcher IC and blown resistors. it started up without issues but blown itself under load... the culprit was a big 450V nichicon capacitor which dried out.. the almost no capacitance caused the active PFC circuit was making spikes killing the switcher.moral of the story - don't assume the big ones are good because they're not bulged... remove them and measure. if the PSU/monitor/whatever is older than 3-4 years then replace the big ones as well especially if it has active PFC... a $4 capacitor is cheaper than replacing half the parts once again

author: BradC
author_rank: Super Contributor
timestamp: June 09, 2016, 04:34:49 am
content: A non-electro related data point.I've just had to repair my Apple Thunderbolt Display for the second time (last time was 2014). Both times it was a MLCC SMD cap on the main secondary rail that had gone low resistance and caused the PSU to drop into protect shutdown.So while most stuff I've repaired has actually been dud electros, there's always one exception to the rule.On caps though. I gave up on Jaycar or Altronics caps years ago. I order from RS and get quality components. Most of them are on the shelf and you get free next day delivery to most places in Aus. Never had an issue with the quality or service, and on the whole the price is not terrible either. You get what you pay for.As far as diagnostics for dicey electros (that are not obviously failed/failing), I've used a combination of freezer spray and a gas soldering iron. Freeze the board until it fails/works, and then one by one heat each electro using the gas soldering iron on the vent cap until you find the dud. The gas-axe is insulated, so no problem doing it live. I've found a lot of borderline caps that looked mint that way. It often works for other thermally sensitive components (usually SMD ceramics in my experience).

author: Section8
author_rank: Contributor
timestamp: June 09, 2016, 06:35:09 am
content: SUCCESSreplaced all the caps and it fired right up just like a new one.Highest ESR measured was 17ohm and the replacements were 0.40. Some of the caps though, were soo far out of spec its amazing it worked at all. 1000uF reading as 228 and 156, 220uF reading as 2000pF etc.Anyway, I've got it going again for about 10 bucks worth of parts and couldn't be happier. Thanks all for your help.Now I'm going to get the other one off the shelf from 6 months ago and replace all the caps on that too (i only replaced the visibly damaged ones that time)

author: Muttley Snickers
author_rank: Unknown
timestamp: June 09, 2016, 07:22:14 am
content: There is nothing more rewarding than fixing stuff, congratulations and well done.Can you list the model and size of the monitor here for future reference ?.Last week our local recycle centre had about a dozen or so 19 inch Viewsonic monitors for 10 bucks each, dated 2009 but still in the boxes and they looked to be very clean, I have enough already so I left them there for the more needy.

author: Section8
author_rank: Contributor
timestamp: June 09, 2016, 07:56:26 am
content: Quote from: Muttley Snickers on June 09, 2016, 07:22:14 amYeah. It was a Viewsonic VG2021m. Its one of the old non-widescreen monitors which I like as having 3 of them on my desk is just right to fill my field of view.