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A VGA monitor may be easier to repair than you think

cnx-software.com

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Re: A VGA monitor may be easier to repair than you think

#111

Post by prewett »

amelius wrote: post #34
nathan_f77 wrote: post #22

Earlier quoted context omitted.

I'm working on a project where I may need to open and repair an old device that probably contains some high-voltage capacitors. Would it be relatively safe to do this if I was wearing rubber gloves + shoes, and used a multimeter to check for voltages, and a large resistor to discharge any capacitors? What kind of bleed resistor is typically used, e.g. for old TVs?

This might be a nice feature of a multimeter: discharge mode. Putting the leads over a capacitor, the multimeter will show the voltage and discharges the capacitor with a constant safe current. Beeps can be used to indicate when the capacitor is safe to handle or not.

It kind of already has a discharge mode, just short the leads of the capacitor with one of the probes.

Re: A VGA monitor may be easier to repair than you think

#112

Post by bityard »

tyingq wrote: post #53
sysadmindotfail wrote: post #43

Earlier quoted context omitted.

I am old. I did not even open the link until you mentioned it was an LCD. I was thinking: "Why would you repair a CRT?"

Comes up fairly often as a nostalgia thing for old Macs, Kaypros, Compaqs, arcade games, and so on.

For most of the last 15 years, if you had an old CRT television or computer monitor, you had actually to pay someone just to get rid of it. Because of the lead shielding used in CRT tubes, they are considered hazardous waste. (Of course, most people were irresponsible or just didn't know any better and just chucked theirs into a dumpster.)

But in the past few years, retro tech has become sufficiently popular due to certain YouTube channels that a CRT TV or monitor in good working condition can now command a worthwhile price.

Re: A VGA monitor may be easier to repair than you think

#113

Post by meemo »

I just had a newish (but out-of-warranty) LG 4k monitor go bad on me. The picture went mostly dark, with a few streaks of white. I figured how to take off the back panel, but then got them stuck removing the EM shield covering the main board. I got all of the screws off, but then it wouldn't come off.

Re: A VGA monitor may be easier to repair than you think

#114

Post by p1mrx »

zbuf wrote: post #107
p1mrx wrote: post #103

Earlier quoted context omitted.

LCD monitors only used VGA because customers didn't know enough to demand DVI. A pixel array is inherently digital, so it makes no sense to put DAC/ADC in the path.

> customers didn't know enough to demand DVI Really, it was more that we didn't have DVI outputs. Its the smartest way to break the chicken-egg situation -- for many (I'd wager the majority) the advantage of a flat panel at first was more about space saving then picture quality.

DVI output was easy; just buy a video card.

The problem is, you can't add DVI to a VGA-only LCD monitor, and those things were everywhere.

Re: A VGA monitor may be easier to repair than you think

#115

Post by scrumper »

mikewarot wrote: post #57

Since 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…

> short any capacitors with a screwdriver

Not universally a good idea to do that, especially not in a power supply. Safe enough in some circumstances but not all. Better to buy a discharge probe or make one by soldering a 2200 ohm 5w resistor between a couple of insulated wires.

EDIT: made it less condescending.

Re: A VGA monitor may be easier to repair than you think

#116

Post by knolan »

I’ve don’t similar fixes over the years soldering replacements for dead components and changing the CCCL in a laptop.

I was surprised by how simple and spacious the boards in these displays are, easy for an oaf like me to replace components on. Just find where the magic smoke came from and order a replacement part for pennies.

Re: A VGA monitor may be easier to repair than you think

#117

Post by foldr »

22c wrote: post #77
jonathanlydall wrote: post #40

I 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 b…

Seems more likely that it would be the voltage rating? While it’s true that a larger capacitance would be fine in many applications, it wouldn’t always be (e.g. if the cap is part of an RC filter or if it’s used as a bypass cap). In contrast the voltage rating of a cap is just a maximum.

Re: A VGA monitor may be easier to repair than you think

#118

Post by deelowe »

sysadmindotfail wrote: post #43
zbuf wrote: post #23

I feel old; I came here for a guide to repair a "VGA monitor" and instead got a flat panel.

I am old. I did not even open the link until you mentioned it was an LCD. I was thinking: "Why would you repair a CRT?"

Lots of older equipment require a CRT to function properly.

Re: A VGA monitor may be easier to repair than you think

#119

Post by ksec »

raxxorrax wrote: post #68
ksec wrote: post #11

Earlier quoted context omitted.

The answer isn't socketed but high quality capacitor ( Solid or Tantalum etc ) . Swollen capacitor should really be a thing of the past. Unfortunately Capacitor is an area that is easiest to cut cost and has no immediate effect on the devices function and are hard to spot. Part of the reason why I switch over to Mac ~20 years ago. I dont want to spend time looking at every capacitor on a motherboard or to gather enou…

> Capacitor marketing on motherboard was a thing. That is a thing? What do they advocate, the fine smell of rotten eggs when they die?

It was a long long time ago, before Solid Capacitor were affordable enough to be used in mainstream electronics. Now they are expected in any quality motherboard. At the time they used to market brands like RubyCon for exceptional stability or another brand which I cant remember for similar marketing reason. And redundant capacitor etc.

Re: A VGA monitor may be easier to repair than you think

#120

Post by eurasiantiger »

klodolph wrote: post #110
eurasiantiger wrote: post #29

Earlier quoted context omitted.

Low ESR only matters for PWM filtering capacitors, such as those found in monitor backlight drivers and some switching power supplies’ secondary circuits. It is not necessary to use such capacitors on the primary side, i.e. when the large capacitor nearest to the mains input dies, just replace it with a normal electrolytic capacitor that matches or exceeds the original’s voltage rating and closely matches its capacit…

Worse yet, sometimes the circuit won't work with a low-ESR capacitor. For example, you can't put a low-ESR capacitor on the output of an LM1117, it will oscillate.

In a pinch, that could be compensated with a resistor, a few ohms would suffice… :)
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