Author Topic: How to fix.  (Read 2679 times)

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Offline In Vacuo Veritas

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Re: How to fix.
« Reply #25 on: September 20, 2018, 04:45:36 pm »

Sure. There are still user groups for Commodore and Amiga stuff. Where are you located? With a name like Serge... BC? Alberta?  ;)
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NB!! :)
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OK that's a bit of a smaller place than Ontario but surely there are still some active user groups in your area? It doesn't need to be Commodore, maybe an Atari or vintage Apple group, they might have a person skilled in CRT repairs.
 

Offline Serge125

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Re: How to fix.
« Reply #26 on: September 21, 2018, 12:56:40 am »
 OK that's a bit of a smaller place than Ontario but surely there are still some active user groups in your area? It doesn't need to be Commodore, maybe an Atari or vintage Apple group, they might have a person skilled in CRT repairs.
[/quote]

No groups where I live city too small for this so... this is why I'm here.
 

Offline Serge125

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Re: How to fix.
« Reply #27 on: September 21, 2018, 01:24:45 am »
Vaporizing a screwdriver on a mains I can see, in a crt HV circuit no.  However, if the current runs through your heart it very well might kill you, so keep one hand in your pocket when poking around.  Remember caps (and the crt) can hold a charge for a significant time so be careful even if you're setting up your instruments when the device is off.

A significant hazard is that if you get zapped and your muscles spasm you might send your tool into the CRT which could implode sending glass everywhere.  Wear safety glasses when working around exposed CRTs.  This is not a huge risk, but your eyesight is worth the bother.

Trouble shooting is a great example of the scientific method.  Observe the behavior (and various measurements), then use your understanding of electronics to form a hypothesis of what is misbehaving to cause the observed behavior.  Finally check the part to verify (or not) your hypothesis.  If you were wrong, think some more and try again.

You should have a plan and be methodical, generally starting with power supplies and then proceed step by step until the problem is found.  When you get a lot of experience you may be able to go directly to the problem.  Do not poke around haphazardly, that's just a waste of time.  First figure out WHAT is not working, then figure out WHY.  Simple. :-DD

It gets interesting when you run into cases of bad engineering and you find the part was doomed to fail.  Or they shaved costs and ran a part close to its limits rather than a more expensive part that wouldn't fail.  You'll see that in consumer gear.

Apropos of nothing other than the vaporized screwdriver story I once watched a tech attempt to put a shorting bar across the line side of a utility meter socket.  I say attempt because it immediately vaporized in his face.  This wasn't on purpose, he was confused about how to install them.  Me?  I was 20 feet away.  He was unhurt but needed a change of pants.   Stupidity does not impress me; I still do mains wiring.

Oh I go through all the process "figure out WHAT is not working, then figure out WHY" every time like for example; No power, ok may not be pluged in (dah), power cord could be broken inside, maybe a blown fuse inside and beyond the fuse is where I stop because I don't know what to do next. Yes I will look if there's any visual problems like burnt components, odd smell, deformed plastic, broken traces, cold solder joints etc... Beyond the fuse I have no idea on how to find shorts or to do trouble shooting. That is why I started to watch for some troubleshooting vids on youtube but mostly it's all hindu or too advance for me. I'd like to see a video that shows me step by step AFTER the fuse.

My monitor I know that the LED in front doesn't light up BUT the fuse isn't broken so I know power supply IS working, there isn't any video on the front screen and at the neck of the tube there isn't any light in it. So there's power going in through the power supply and then I don't know what to do next. There is a very faint wining sound coming out of the speaker and even if the speakers aren't plugged in I hear that faint wining sound. Here's the sound file that I have recorded and been amplified to have a better sound.

THANKS!!!
 

Offline BrianHG

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Re: How to fix.
« Reply #28 on: September 21, 2018, 02:10:48 am »
Hi Serge,

welcome to the forum. Great, that you are interested in fixing stuff.

However, a CRT-Monitor is DEFINITIVELY NOT a device to learn trouble shooting on ...
There are lethal voltages all over the place and also true high voltage stuff. Capacitors might hold the charge even when not plugged in and, to make matters worse, often everything is literally crammed into the case which doesn't actually help troubleshooting a lot ...

At least you would need an isolation transformer, a decent SAFE multimeter and probably some differential probes and a scope... and A LOT OF EXPERIENCE ...

Anyway - A CRT Monitor? Just not worth the risk!

Hi and THANKS for your reply. Well for A CRT monitor? Just not worth the risk well in my case is worth the risk because it's a Commodore and I need this monitor for my Amiga 500 and it only syncs at 15khz for Amiga rgb so today's monitor doesn't do this so I really need this monitor. Right now I have it setup on a tv but it's NOT very clear compared to my monitor.

THANKS!!!  ;-)
Good for all Amiga RGB outputs.  Also de-interlaces.  Feed any flat panel VGA monitor, flicker free.

RGB 15khz to VGA upsampler
RGB 15khz to HDMI upsampler

Noise Patch for the GBS-8220:

« Last Edit: September 21, 2018, 02:40:22 am by BrianHG »
__________
BrianHG.
 

Offline cdev

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Re: How to fix.
« Reply #29 on: September 21, 2018, 03:36:33 am »
Fixing old style CRTs IS DANGEROUS and should not be done unless the CRT is something really special and unique. You should also have and follow the manufacturers service manual.

Old CRTs are not so good for your eyes. Most of them are probably not long for this world. And they weigh a lot too and can cause a potentially dangerous implosion if you break one.
"What the large print giveth, the small print taketh away."
 

Offline james_s

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Re: How to fix.
« Reply #30 on: September 21, 2018, 03:55:47 am »
Oh come on now, quit with the hyperbole. We used CRTs for decades without people dying left and right. You'd really have to try in order to make one implode without completely removing it from the monitor and smashing it with a hammer or dropping it on concrete. I've been repairing CRT displays for ~25 years and after working on hundreds of them I have yet to ever seriously injure myself. I was poking around inside old TVs by the time I was 12, several years before I finally learned to actually fix them. They are not appreciably more dangerous to work on than any other equipment that has a mains connected switching power supply. Use a little common sense and you will be fine.

Yes you can easily drive a flat panel LCD from a vintage computer but it looks like shit. A CRT monitor has a really unique look and on a retro machine anything else just looks wrong. It's like a 1930s-40s classic car with an automatic transmission, it's possible to do and people do it but it's stupid.
 

Online PaulAm

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Re: How to fix.
« Reply #31 on: September 21, 2018, 12:51:31 pm »
Quote
Oh I go through all the process "figure out WHAT is not working, then figure out WHY" every time like for example; No power, ok may not be pluged in (dah), power cord could be broken inside, maybe a blown fuse inside and beyond the fuse is where I stop because I don't know what to do next. Yes I will look if there's any visual problems like burnt components, odd smell, deformed plastic, broken traces, cold solder joints etc... Beyond the fuse I have no idea on how to find shorts or to do trouble shooting. That is why I started to watch for some troubleshooting vids on youtube but mostly it's all hindu or too advance for me. I'd like to see a video that shows me step by step AFTER the fuse.

My monitor I know that the LED in front doesn't light up BUT the fuse isn't broken so I know power supply IS working, there isn't any video on the front screen and at the neck of the tube there isn't any light in it. So there's power going in through the power supply and then I don't know what to do next. There is a very faint wining sound coming out of the speaker and even if the speakers aren't plugged in I hear that faint wining sound. Here's the sound file that I have recorded and been amplified to have a better sound.


No, you don't know the power supply is working, only that power might be going into it.     Have you measured the AC line going into the actual power supply?  What are the output voltages?  What is the ripple on the output rails? If you can answer those questions, only then can you say the power supply is working, then you can start looking at the next piece of the puzzle.

If you see a problem there, what type of power supply is it?  Linear or switching?  That makes a big difference in how you troubleshoot.

You're assuming the power supply is working without verifying that, which is a mistake.  The LED not lighting up is a clue that the power supply may have a fault (it might also be a shorted cap on the power rails somewhere) but you won't know unless you actually measure it.

A shorted cap somewhere may pull the power supply voltage down enough so some of the circuitry doesn't work, but not draw enough current to blow the fuse.

If you don't have a schematic, it gets tougher.  Look for fixed output regulator chips which will tell you what the voltage should be.  The filter cap voltage rating will give you a clue as well.  Look for parts which get very hot which may indicate a short.  Linear regulators may run hot, so you need to have an idea about what's going on.
 

Offline james_s

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Re: How to fix.
« Reply #32 on: September 21, 2018, 03:40:04 pm »
The schematic and some related service information was already posted in this thread.

http://personalpages.tds.net/~rcarlsen/cbm/monitors/1084s-d/

It uses a switching power supply based on the STK73410, datasheet for that is online.

The very first thing I'd check is the horizontal output transistor, that is a fairly common failure and if it is shorted it will cause the monitor to be dead. The HOT is Q202 in this monitor.

 

Offline Bashstreet

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Re: How to fix.
« Reply #33 on: September 21, 2018, 04:54:46 pm »
Yeah just remember be careful it is best not mess with CRT's unless you know what your doing and how to take precautions.

Stay safe and good luck ! :-+
 

Offline Serge125

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Re: How to fix.
« Reply #34 on: September 21, 2018, 06:37:02 pm »
The schematic and some related service information was already posted in this thread.

http://personalpages.tds.net/~rcarlsen/cbm/monitors/1084s-d/

It uses a switching power supply based on the STK73410, datasheet for that is online.

The very first thing I'd check is the horizontal output transistor, that is a fairly common failure and if it is shorted it will cause the monitor to be dead. The HOT is Q202 in this monitor.

Ok how do I do this check??? Do I need to discharge the flyback and that big cap?? Do I have to remove it from the board or leave it there. Like I said I NEVER DID ANY ONBORD CIRCUT TESTING, so do some very good explaining on how to do this.

THANKS for any help!!
 

Offline Serge125

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Re: How to fix.
« Reply #35 on: September 21, 2018, 11:35:52 pm »
Hi Serge,

welcome to the forum. Great, that you are interested in fixing stuff.

However, a CRT-Monitor is DEFINITIVELY NOT a device to learn trouble shooting on ...
There are lethal voltages all over the place and also true high voltage stuff. Capacitors might hold the charge even when not plugged in and, to make matters worse, often everything is literally crammed into the case which doesn't actually help troubleshooting a lot ...

At least you would need an isolation transformer, a decent SAFE multimeter and probably some differential probes and a scope... and A LOT OF EXPERIENCE ...

Anyway - A CRT Monitor? Just not worth the risk!

Hi and THANKS for your reply. Well for A CRT monitor? Just not worth the risk well in my case is worth the risk because it's a Commodore and I need this monitor for my Amiga 500 and it only syncs at 15khz for Amiga rgb so today's monitor doesn't do this so I really need this monitor. Right now I have it setup on a tv but it's NOT very clear compared to my monitor.

THANKS!!!  ;-)
Good for all Amiga RGB outputs.  Also de-interlaces.  Feed any flat panel VGA monitor, flicker free.

RGB 15khz to VGA upsampler
RGB 15khz to HDMI upsampler

Noise Patch for the GBS-8220:


THANKS checking it out just in case things doesn't work out!!!
 

Offline james_s

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Re: How to fix.
« Reply #36 on: September 22, 2018, 05:01:52 am »
Ok how do I do this check??? Do I need to discharge the flyback and that big cap?? Do I have to remove it from the board or leave it there. Like I said I NEVER DID ANY ONBORD CIRCUT TESTING, so do some very good explaining on how to do this.

THANKS for any help!!

You really should learn the basics and practice troubleshooting low voltage stuff before you poke around inside any mains powered gear. At the bare minimum you should be proficient at testing transistors and diodes with a multimeter.

No need to remove anything from the monitor, just shut it off and wait a few minutes and the CRT will discharge itself through the focus divider. The bulk filter capacitor usually will discharge itself but in some monitors a fault condition can prevent it from discharging, so best to measure the voltage with a multimeter.
 


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