Monitor repair questions

[otacon14112]

I got a relative's computer and monitor a few years ago. The monitor would actually be more useful to me since the computer is several years old, so I tried it out. Unfortunately, it doesn't work. I just recently got around to looking at it. I found the service manual here: https://www.manualslib.com/manual/26940 ... =33#manual

There are some things that are a little confusing, though:

1. The service manual says what to do if the monitor doesn't have power, and if there's no picture and the LED is orange. Well, it's kind of neither. When a power cord is plugged into it, the LED flashes approx. once per second with a dim white light. So there's obviously some power to it, but I don't know if they are talking about the actual LCD display, or any part of the monitor as a whole in general.
2. The component labels in the schematics don't match the labels on the circuit boards, and CN701 has 12 pins in the schematic, but there is no 12-pin connector on the circuit board. But after doing a little research and reasoning, I think I found the 2 transistors the flow chart talks about, and an 8-pin connector that I think is the functional equivalent of CN701 in the schematic.

With everything out in the open and connected, I noticed a clicking sound when the LED in the power button flashes. What do you guys think about the two issues above?

I'll look at the crystal it talks about when I get home later. Thanks!

[RollyShed]

Just a quick reply before I head out to teach computing.
Fig 10 - do any of those black tube like things with metal tops have bulged tops?
If so they need changing. They are capacitors.

I haven't scrolled back on your link yet to see make and model - Arrh yes! Acer AL1916. And yes, I've fixed numerous monitors though none of those - yet.

[151tom]

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[otacon14112]

Just a quick reply before I head out to teach computing.
Fig 10 - do any of those black tube like things with metal tops have bulged tops?
If so they need changing. They are capacitors.

I haven't scrolled back on your link yet to see make and model - Arrh yes! Acer AL1916. And yes, I've fixed numerous monitors though none of those - yet.

Yeah, most of them are bulging. I wrote down their values to see if I have any around the house. Would that cause the clicking that occurs simultaneously with the power button LED flashing? Do you think that could be the reason it's not working?

[RollyShed]

Here is a good link showing what bad capacitors look like -
https://rollestonshed.wordpress.com/com ... -problems/

The black marks are just felt tip pen but it is also likely that a brown stain will appear on a faulty capacitor as it leaks as well as bulging.

The clicking, the power supply half going and failing to start - most likely.

The capacitor problem started with those made between the years ~2000 - 2005 and a Google search will give a fuller story. One version was the recipe was stolen but not the complete version so they didn't get it right. Partially folklore, partially right.

I've replaced hundreds over the last decades. Typical, a University Department with computers for teaching and 40-50 computers with their supplies, and the monitors too, means a steady run of fixing.

[151tom]

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[RollyShed]

Replacing capacitors isn't a hard thing to do although soldering skills and patience is a must.

Getting the polarity right is also accentual. The original ones and the replacements should be well marked.

[151tom]

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[otacon14112]

Sorry for not replying sooner; a lot of stuff is happening in my life right now I haven't even gotten around to hooking the crystal up to my o'scope yet.

Here is a good link showing what bad capacitors look like -
https://rollestonshed.wordpress.com/com ... -problems/

The black marks are just felt tip pen but it is also likely that a brown stain will appear on a faulty capacitor as it leaks as well as bulging.

The clicking, the power supply half going and failing to start - most likely.

The capacitor problem started with those made between the years ~2000 - 2005 and a Google search will give a fuller story. One version was the recipe was stolen but not the complete version so they didn't get it right. Partially folklore, partially right.

I've replaced hundreds over the last decades. Typical, a University Department with computers for teaching and 40-50 computers with their supplies, and the monitors too, means a steady run of fixing.

I get that bulging caps are bad and need replaced, but what do they cause, functionally? What symptoms are caused by them? I was thinking the power supply was faulty. Could you clarify the bolded part a little bit please? Thanks

And it sounds like you have plenty of fun!

[DAMIEN1307]

Capacitors simply are "resevoirs" for the storage of electrical power and allow it to be released through the circuitry in a controlled manner, not unlike a water storage resevoir...when they start bulging etc, they are "leaking" the stored power that the system relies on for a steady, regulated power source...that is about as simple as i can put it without being overly technical...DAMIEN

[RollyShed]

Capacitors - voltage storage yes but....

The supply is AC (Alternating Current) from your power socket, 60 cycles (60 Hz) in USA, 50 cycles (50 Hz) in many other countries and it is rectified (using diode(s). That is, it is made into a DC (Direct Current) voltage = the ripple goes in one direction.

We want to store the peak voltage (or near it) and get rid of the ripple so that is fed, from the rectifier diode(s), into the capacitor. The output current from the capacitor to the rest of the circuitry is low enough (or should be) not to empty the capacitor between each positive ripple. Capacitors which have bulged tops have lost capacity and we now have ripple.

Note the capacitor and rectifier can be wired the other way round and can store a negative voltage.

So from this, the clicking can be caused by the voltage going positive and causing a start-up but not staying positive long enough to keep things going because the capacitor isn't keeping that voltage up between each positive ripple.

And it sounds like you have plenty of fun!

A lifetime of "fun". That was my job, electronics which eventually included computers. Someone once said, "DC to daylight?"
"No, it was DC all the way up to Xrays, you name it we did it."

As for computers, the worst thing was getting rid of punched cards for programming. What do you write your shopping list on now? OK use the back of an envelope. No, they are going to do away with postage (mail) too.

[151tom]

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[RollyShed]

As for computers, the worst thing was getting rid of punched cards for programming. What do you write your shopping list on now?

Use Quick Memo on your smartphone for your shopping list.

And "Ooopps", the battery has gone flat - again.....

[151tom]

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[Portreve]

My dad would have enjoyed this discussion. He ate, drank, and lived electronics at the component level. He worked for NASA at what is now the John Glenn Research Center in Brookpark, Ohio (it adjoins Cleveland Hopkins International Airport and shares some of their field and runways) as an electronics technician, and did a lot of troubleshooting work as well as original builds. He used to win awards for his soldering prowess.

Sadly, when it comes to that particular area of interest and skill, I inherited none of it.

When he died in 2008, I had a ton of capacitors, resistors, nor gates, switches, transistors and God knows what all else to get rid of. I tried to sell it but nobody was interested. I wanted to donate it but nobody would take it.

[Hoser Rob]

...I get that bulging caps are bad and need replaced, but what do they cause, functionally? What symptoms are caused by them?...

Thre's no one answer for this, you can't say without knowing what part of the circuit they're in. Also, if there are that many faulty caps it's being caused by something else.

[otacon14112]

when they start bulging etc, they are "leaking" the stored power that the system relies on for a steady, regulated power source

Capacitors which have bulged tops have lost capacity and we now have ripple.

the clicking can be caused by the voltage going positive and causing a start-up but not staying positive long enough to keep things going because the capacitor isn't keeping that voltage up between each positive ripple.

Alright, thanks. Almost all of my electronics experience is based on digital systems. I don't have much experience with analog circuits. So I don't know many symptom causes.

[otacon14112]

My dad would have enjoyed this discussion. He ate, drank, and lived electronics at the component level. He worked for NASA at what is now the John Glenn Research Center in Brookpark, Ohio (it adjoins Cleveland Hopkins International Airport and shares some of their field and runways) as an electronics technician, and did a lot of troubleshooting work as well as original builds. He used to win awards for his soldering prowess.

Sadly, when it comes to that particular area of interest and skill, I inherited none of it.

When he died in 2008, I had a ton of capacitors, resistors, nor gates, switches, transistors and God knows what all else to get rid of. I tried to sell it but nobody was interested. I wanted to donate it but nobody would take it.

I would LOVE to have a friend like that. None of my friends are into electronics/hacker-ish stuff. I would have gladly accepted those parts lol, and I would have gladly paid the postage.

Also, if there are that many faulty caps it's being caused by something else.

Thanks for mentioning this. It would suck to replace all those caps just to have them go bad again. Now I'm going to start studying what causes caps to bulge lol.

[chazz_tsc]

I'll just quickly comment that caps do fail with age, and especially the ones in modern power supplies tend to, because the high frequencies involved put a strain on them. Typically these days, you'll have a diode bridge that feeds a single big capacitor, which feeds a couple of switching transistors, which feed a teeny little transformer; and the output of the transformer is again rectified and fed through smaller capacitors. The switching frequency is typically up around 25,000 Hz or faster, because that way they can make the transformers smaller and lighter. But that high frequency is not good for electrolytic capacitors, and they do heat, bulge, and pop over time.

The big cap on the input side will typically be rated 300V. It almost certainly hasn't failed. The ones on the output are rated 16 or 25V usually, and 1500 - 3300 microfarads, they'll have died.

The click is the power supply starting up, detecting an unacceptable amount of ripple in the output, and shutting down again.

[otacon14112]

I'll just quickly comment that caps do fail with age, and especially the ones in modern power supplies tend to, because the high frequencies involved put a strain on them. Typically these days, you'll have a diode bridge that feeds a single big capacitor, which feeds a couple of switching transistors, which feed a teeny little transformer; and the output of the transformer is again rectified and fed through smaller capacitors. The switching frequency is typically up around 25,000 Hz or faster, because that way they can make the transformers smaller and lighter. But that high frequency is not good for electrolytic capacitors, and they do heat, bulge, and pop over time.

The big cap on the input side will typically be rated 300V. It almost certainly hasn't failed. The ones on the output are rated 16 or 25V usually, and 1500 - 3300 microfarads, they'll have died.

The click is the power supply starting up, detecting an unacceptable amount of ripple in the output, and shutting down again.

Awesome! Thank you very much for taking time to share your knowledge and experience. This helps me a lot.

And thanks again to everyone who contributed. Have a good Thanksgiving to everyone who celebrates it.