CRT monitor gone AWOL(please help)

[TechGeek]

Hi, everybody. I am trying to restore an 18 year old Gateway 2000 Vivitron 17 CRT monitor. I started work on it yesterday. I used some sandpaper to sand some rust off of a panel that covers the traces in the neck socket board. Today, I cleaned up the monitor with some Ultra Duster and let it air out for 10-20 minutes and closed it up. I moved it into our garage and plugged it into an extension cord so that I wouldn't be risking myself when plugging it in/unplugging it. I plugged it in and heard popping noises. I immediately unplugged it. They were quiet, as if it was a fire. I watched for several minutes to make sure that there was no fire. I had my mom plug it in for a second time. Once it was plugged in, there was a loud "BUZZZZZZ" from the monitor and I immediately yelled, "UNPLUG IT!" That was that. It hasn't had power since, nor have I came to retrieve it. Before then, it was unplugged for about 2 years and exposed to the weather. I didn't see any bulging/blown caps. What fried? What else should I do? Should I change the flyback? Please help.

[Agent24]

Re: CRT monitor gone AWOL(please help)

If it was exposed to weather there is probably dirt\corrosion you missed causing arcing, in the main PSU or in the high-voltage section, if that's even starting up...

But the truth is, anything that has been outside for 2 years is pretty much beyond economical repair, if it's been rained on it will likely have corrosion in many places... for a 17" CRT it's hardly worth it unless you want a learning exercise...


If you're still keen - have a look at this first: http://www.repairfaq.org/samnew/tvfaq.htm and check all the safety stuff for a start. It's about CRT TVs but CRT monitors are the same, aside from the different video signal processing circuitry.


In terms of actual repair - what did it originally die of?
Upload as many photos as you can take of the insides.
See if you can find the source of the arcing you heard - check the PSU, HV section, tube socket, neck board, EHT connector for sighs of arcing. Don't poke your fingers under the anode cover without discharging the tube first!

At some point you will probably have to plug it back in the with the cover off and see where the arcing is coming from.

[TechGeek]

Re: CRT monitor gone AWOL(please help)

Where is the EHT connector, and I've watch enough YouTube to know to not do that. Also, when I plug it in to check for arcing, I'm going to do it WAY away from the garage, have a fire extinguisher ready (in case something goes south), and I'm going to turn the power on/off via the garage breaker.

[Agent24]

Re: CRT monitor gone AWOL(please help)

EHT\Anode connector is under the the big (usually black) rubber cover on the side of the CRT with the thick (usually red) wire coming out of it. At the other end is the flyback unit.

For now, inspect and take photos if you can, it may be something obvious we can spot...

If you plug it in again before then, do it with the lights off etc so any arcing is more obvious. The noise is usually louder than the spark you might see.

[TechGeek]

Re: CRT monitor gone AWOL(please help)

Also, if I unplug a running monitor, will the flyback lose it's stored power because it was discharging to the display?

[Agent24]

Re: CRT monitor gone AWOL(please help)

Yes. The flyback is just a transformer, it can't store power after being turned off\unplugged etc.

But, the 'flyback unit' in modern CRT displays has, as well as the transformer, an inbuilt voltage multiplier (in old CRT TVs this is a separate 'tripler' unit) which includes some capacitors which may stay charged with some voltage - although you cannot access these except the output of the multiplier, which is connected to the CRT anode wire.


The biggest things you have to worry about are the mains filter capacitor(s). These are easily accessible and will store a couple of hundred volts and will give a nasty shock if you don't discharge or wait for them to discharge first.

They are also more dangerous if you need to measure the voltage across them during operation. Probing them is fine if you are confident and careful, but it is much safer to clip leads to the legs (or solder wires to them) and measure them without having to hold probes - that way your hands can't slip and accidentally touch them or anything else on the hot\mains side which could be fatal.


The CRT itself also acts as a capacitor and stores some charge from the EHT output. This is accessible at the anode connector, but the rubber cover prevents you from getting shocked as long as you don't go poking underneath it.

The problem is, if there is enough dust\dirt\grime etc around the anode connector, it can start arcing across the glass to ground (the outside of the tube is connected to ground by the silver wire that looks similar to solder braid and attached with springs. This makes contact with the grey paint (aquadag) on the outside of the tube)

If the anode connector is the source of your arcing, you will need to discharge the tube, remove the anode cover, and clean the bare glass area around it well. Do not clean outside this area and take off the aquadag! You should also clean the anode cover underside too, in case there are conductive residues on it from arcing.


If you do need to discharge the tube, for cleaning etc:
Make sure the monitor is unplugged!
Then, clip an insulated jump lead from the CRT grounding braid to the shaft of a plastic-handled flathead screwdriver, and poke the screwdriver under the anode cover until you contact the metal underneath and (most likely) hear a pop\snap as the tube discharges to ground. If you don't hear anything, try again, but most likely there was either not enough voltage to make a noise or the tube had already discharged by itself (some designs can do this)

[TechGeek]

Re: CRT monitor gone AWOL(please help)

What is the aquadag?
Also, is it safe to power on a monitor after it arcs to somewhere w/o cleaning it? Also, how do you plug the anode connector back in without it being a pain in the rear?

[Agent24]

Re: CRT monitor gone AWOL(please help)

The aquadag is conductive paint that is applied to most of the outside (and most of the inside) of the CRT itself. It's the grey\black, graphite-looking stuff. Note the difference between the clear glass area around the neck of the tube, and the clear area around the anode connector (sometimes painted red)

The two layers of aquadag actually form a capacitor, with the tube glass as dielectric, which is why the CRT has to be discharged if you are playing around with it.


You can power it on 'safely' in the sense it is unlikely to hurt you. (though safety glasses are a good idea, just in case) But if you power it on for too long you may damage components, burn traces etc. If you inspected the boards etc and couldn't see any obvious evidence of arcing anywhere, you pretty much just have to power it up and see where the arcing is coming from.

Plugging the anode connector back in can be a bit annoying, some have very tight clips or springs. For the tough ones it can be easier to put one side in first, and help the other side in with the screwdriver. That's what I do, anyway...

[TechGeek]

Re: CRT monitor gone AWOL(please help)

Thanks! When I have to power up the monitor, do you want me to take video and post it, and is it also a good idea to power on the thing via breaker? Also, why do you not want to remove the aquadag?

[Agent24]

Re: CRT monitor gone AWOL(please help)

You could take video, but it is probably not necessary, and will likely just get in the way of trying to see what is happening.

Edit: Photos of the power supply circuitry and HV sections as-is would be pretty useful, though.

I'd just put it on the end of a cord and switch it on and off at the wall, probably easier.

The aquadag is part of the CRT design and is required to be there. if you removed it, the CRT would probably not work too well afterwards...
I only mention that because after talking about cleaning, someone could mistake the aquadag for dirt\dust etc and try to clean it off as well.

[TechGeek]

Re: CRT monitor gone AWOL(please help)

Yes. The flyback is just a transformer, it can't store power after being turned off\unplugged etc.

But, the 'flyback unit' in modern CRT displays has, as well as the transformer, an inbuilt voltage multiplier (in old CRT TVs this is a separate 'tripler' unit) which includes some capacitors which may stay charged with some voltage - although you cannot access these except the output of the multiplier, which is connected to the CRT anode wire.


The biggest things you have to worry about are the mains filter capacitor(s). These are easily accessible and will store a couple of hundred volts and will give a nasty shock if you don't discharge or wait for them to discharge first.

They are also more dangerous if you need to measure the voltage across them during operation. Probing them is fine if you are confident and careful, but it is much safer to clip leads to the legs (or solder wires to them) and measure them without having to hold probes - that way your hands can't slip and accidentally touch them or anything else on the hot\mains side which could be fatal.


The CRT itself also acts as a capacitor and stores some charge from the EHT output. This is accessible at the anode connector, but the rubber cover prevents you from getting shocked as long as you don't go poking underneath it.

The problem is, if there is enough dust\dirt\grime etc around the anode connector, it can start arcing across the glass to ground (the outside of the tube is connected to ground by the silver wire that looks similar to solder braid and attached with springs. This makes contact with the grey paint (aquadag) on the outside of the tube)

If the anode connector is the source of your arcing, you will need to discharge the tube, remove the anode cover, and clean the bare glass area around it well. Do not clean outside this area and take off the aquadag! You should also clean the anode cover underside too, in case there are conductive residues on it from arcing.


If you do need to discharge the tube, for cleaning etc:
Make sure the monitor is unplugged!
Then, clip an insulated jump lead from the CRT grounding braid to the shaft of a plastic-handled flathead screwdriver, and poke the screwdriver under the anode cover until you contact the metal underneath and (most likely) hear a pop\snap as the tube discharges to ground. If you don't hear anything, try again, but most likely there was either not enough voltage to make a noise or the tube had already discharged by itself (some designs can do this)

Can I ground to the Earth?

[Agent24]

Re: CRT monitor gone AWOL(please help)

Grounding to the tube grounding braid\frame is the best idea. Using other ground points like signal ground etc may damage the circuitry.

[TechGeek]

Re: CRT monitor gone AWOL(please help)

Signal ground?! I don't even know where THAT is, let alone the respective board!

[Agent24]

Re: CRT monitor gone AWOL(please help)

Signal ground?! I don't even know where THAT is, let alone the respective board!

Signal ground woud be the ground on the video input for example, or any ground point in the video processing circuitry etc. Discharging through that may (or likely will) cause damage to the ICs etc. At several kV from the tube, it's a scenario similar to an ESD event.

It's safest and easiest to just discharge the CRT into its own ground point, that way the discharge path is safely away from any other parts which may be potentially damaged.


On another note: Where are the photos of this thing already?

[stj]

Re: CRT monitor gone AWOL(please help)

i'm surprised i didnt see this thread faster.

some starting points.
1: unplug the degausing coil from the board, it will hum like a bastard and scare the hell out of you for a couple of seconds.
best to avoid that till you have a picture.

2: the tube can hold several thousand volts for upto a month - maybe longer so dont touch the anode connection.

best thing is to do this in 2 halves - the psu half and the monitor half.
can you find a schematic?
because it will make it a lot simpler to stop power reaching the lopt.


then your just fixing/testing a 120-180v switching psu.

and remember: it's not the shock that kill's you - it's the thing you hit your head on when you get thrown!!

[TechGeek]

Re: CRT monitor gone AWOL(please help)

Signal ground woud be the ground on the video input for example, or any ground point in the video processing circuitry etc. Discharging through that may (or likely will) cause damage to the ICs etc. At several kV from the tube, it's a scenario similar to an ESD event.

It's safest and easiest to just discharge the CRT into its own ground point, that way the discharge path is safely away from any other parts which may be potentially damaged.


On another note: Where are the photos of this thing already?

I've been forgetting to take photos of it. Also, I have a screwdriver long enough to touch the anode and the ground frame at the same time. Can I ground the tube by bridging the anode and ground frame with the screwdriver?

[Agent24]

Re: CRT monitor gone AWOL(please help)

I've been forgetting to take photos of it. Also, I have a screwdriver long enough to touch the anode and the ground frame at the same time. Can I ground the tube by bridging the anode and ground frame with the screwdriver?

I guess so but I can't imagine it will be easy unless your screwdriver can go around corners?

[TechGeek]

Re: CRT monitor gone AWOL(please help)

It's actually really easy. The ground frame and anode are parallel to each other.

[stj]

Re: CRT monitor gone AWOL(please help)

that stupid trick can damage diodes in the lopt.

if you need to discharge a tube, get some 1meg high voltage resistors and solder them in series , put them in something like a plastic pipe for safety with some high-voltage wire coming out of each end to short under the cap with.

[Agent24]

Re: CRT monitor gone AWOL(please help)

that stupid trick can damage diodes in the lopt.

How? I don't see how the diodes can be damaged, you are not discharging through them or anything - worst I can imagine is arc damage to the anode connector\screwdriver, but please tell me if there's something I've missed!

Of course one should use the proper tool, but this thread is about a crusty old 17" CRT that's been outside for 2 years...