How do you find a broken capacitor on a board?
The article says it was clear that the cap was "swollen" but how do I know what a swollen cap looks like?
And what if it's broken but not swollen?
A VGA monitor may be easier to repair than you think
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Re: A VGA monitor may be easier to repair than you think
#72Since the title specified a resolution, I assumed a VGA CRT with a DB15 connector. (Not an MDA, CGA or EGA) I was all set to warn you kids about the dangers of CRTs, high voltage, Xrays, and of course the implosion if you break the neck of the tube... and instead got bad capacitors on LCD displays. Regardless of what the safety standards say, you should always remove power, and short any capacitors with a screwdriver…
Thanks. I appreciate when someone gives safety advices as they come in handy when starting to tinker electronics. When repairing dishwasher I had to disconnect a huge capacitor... well it looked like it. Knowing what you just wrote about capacitors, it gave me shrugs and I was VERY careful handling that piece of thing. Can you give any advice on what good fume extractor for soldering does and if hobbyist that does re…
Solder fumes aren't great for your lungs, but its not a severe health threat: you're not soldering that much. A fan blowing at you to keep smoke and fumes out of your face should be sufficient for up to a few hours a day of soldering. If others in the house complain about the smell, then work on venting outside harder.
Re: A VGA monitor may be easier to repair than you think
#73How do you find a broken capacitor on a board? The article says it was clear that the cap was "swollen" but how do I know what a swollen cap looks like? And what if it's broken but not swollen?
you look for a short and try to isolate the section. there are lot of videos on youtube. try eevblog and old rossmann videos. electronic repair school is also good.
edit: you will be able to tell a swollen cap, but if you are not sure you should definitely learn the basics first. large caps can store a charge and can hurt you.
Re: A VGA monitor may be easier to repair than you think
#74How do you find a broken capacitor on a board? The article says it was clear that the cap was "swollen" but how do I know what a swollen cap looks like? And what if it's broken but not swollen?
look at the other capacitors. the top is really flat. you can even spot those that start to fail because light will reflect slightly differently on top of them.
Re: A VGA monitor may be easier to repair than you think
#75Power supply caps fail so often that maybe they should be socketed?
so, you are not a business guy huh? lol plus it's more work & cost more to include sockets.
Re: A VGA monitor may be easier to repair than you think
#76Why is "VGA" mentioned? Does the fix only apply to monitors with a VGA interface? This looks applicable to any monitor with a internal power supply.
You can do that to any monitor, even recent ones.
Re: A VGA monitor may be easier to repair than you think
#77I did this kind of a repair job to a couple of Samsung 23" 1080p screens back in 2012. A friend gave them away since their backlights would flicker making the monitor unusable for the first 10 or so minutes after they were turned on, after which they worked completely fine. I have little to no knowledge of electronics, but did know how to use a soldering iron. As I recall, I watched a YouTube video and was confident…
>they had available on hand had a different "number" on it, but they assured me it was a higher rating and wouldn't affect use
It's probably the amount of farad units the capacitor is rated for. You can often use a capacitor with higher farads as long as the voltage is the same and it can be even more reliable than the original part, the only trouble is sometimes they are physically larger or taller, so you have to be careful if you're working in tight spaces.
Re: A VGA monitor may be easier to repair than you think
#78How do you find a broken capacitor on a board? The article says it was clear that the cap was "swollen" but how do I know what a swollen cap looks like? And what if it's broken but not swollen?
It's very noticeable when you pay attention and compare it to the others. There are generally a lot of capacitors there, and only one or two will be swollen (the top part is supposed to be flat or even slightly curved inward, if it's curved upward, it's bad). Really, if it even looks slightly out of place, change it, capacitors are dirt cheap.
I'm not sure it can be broken without being swollen, or at least that's not a frequent failure mode.
Having repaired a few displays just like that, I can say it's really easy provided you are able to open the display and solder on a basic level, which anyone can learn in an afternoon.
On the other hand, not all display will be that easily repaired. Sometimes, you cannot easily identify any swollen capacitors, or there is a burn mark somewhere else, or something else that you cannot identify (and thus order a replacement for). In those cases, unfortunately it generally doesn't make sense to bring it to a shop to be repaired by pros.
Re: A VGA monitor may be easier to repair than you think
#79Earlier quoted context omitted.
Huh. I have a Dell monitor that suddenly started showing these kind of smeared stripes instead of a proper picture. Took it apart, looked carefully at all the capacitors and other components on both boards, but none looked bad. Disconnecting and reconnecting the ribbon that goes to the LCD panel made no difference whatsoever. What could it possibly be?
does a bad capacitor always show damage visibly?
Most likely it will simply NOT power on. That or briefly power on and shut off once the ripple spikes and glitches everything.
In another post here I mentioned fixing Optiquest monitors. The usual issue was you would press the power button and the power LED would flah for a second and... nothing. This is because the output cap of the switching supply would cease to filter the high speed square wave that goes through the transformer. So your DC power supply is now an AC square wave supply. Of course logic circuits don't like that so they will outright fail.
Sometimes there is enough capacitance via decoupling caps, ground planes on the PCB and local filter caps on the logic board so the initial power up works but once the load increases the ripple increases until it becomes AC again and everything goes haywire or shuts down.
Re: A VGA monitor may be easier to repair than you think
#80Earlier quoted context omitted.
What do bleed resistors drain towards if the ground wire has been unplugged by unplugging the monitor?
A charged capacitor has a surplus of electrons on one side, and a shortage on the other. A bleed resistor allows current to flow from one side to the other, balancing the charges on both sides so there is no relative voltage. Q=CV
Thank you! I understand this now.