CRT monitor gone AWOL(please help)

[TechGeek]

Re: CRT monitor gone AWOL(please help)

I'll try to get good pictures tomorrow.

[momaka]

Re: CRT monitor gone AWOL(please help)

^ Well it is a Vivitron... hint hint hint .

Seriosuly, at this point, we need pictures to troubleshoot the monitor. The OP seems inexperienced (sorry TechGeek, no offense here) so a schematic won't do as much good IMO...

And no, plugging in the monitor again and filming a video won't be any good either, unless you just want to finish burning it up and throw it away after that.

See this thread and use the incandescent bulb trick next time before you power it on:
https://www.badcaps.net/forum/showpo...4&postcount=70

As far as discharging the tube - that likely isn't necessary as Trinitrons have a built-in discharge mechanism. That said, if you will be removing the anode cap to get the boards out, then do try to discharge it, just in case. I usually use the aligator clip and screwdriver trick, but with one addition: I have a 4.7 KOhm 5W resistor to limit the current so that I don't get a huge spark. You don't need to have exactly that kind of resistor. Any resistor that is 1 KOhm or more and rated for at least 1W of power or more will do. But again, this is not necessary. As agent_24 noted, it's a "crusty" 17" CRT .

The thing you should be most worried about is the large bulk cap on the input. That one can store 170V to 340V (depending on your line voltage, but since you are in the USA, it would be the former). You definitely don't want to touch its leads or anything that is connected to them. It likely won't kill you, but it will hurt enough to remember it, especially if you discharge it through your entire body (i.e. current entering through one hand and exiting through the other). I discharged those kind of caps through my thumb a few times before and IT HURTS! Best case it will feel like a nasty bee sting. Worst... it hurts okay.
So anyways, as you are taking the board out, avoid touching the primary side or any components on it. Better yet, if you can discharge that bulk cap before you begin taking out the board, that would be even better.

I myself was working today on a 17" Sony CRT with a PSU problem. Will be discharing the bulk cap tomorrow before pulling out the boards. There's a way, but you need to know what you are doing. And without pictures, I can offer you zero advice on that.

[stj]

Re: CRT monitor gone AWOL(please help)

looks a bit like a sony.

[budm]

Re: CRT monitor gone AWOL(please help)

Gateway 2000 VIVITRON full model number?
CPD-??????
I.E.:
http://www.ecrater.com/p/14542471/ga...monitor-17-cpd ??????

We need good clear pictures to see what condition of this monitor is.

[stj]

Re: CRT monitor gone AWOL(please help)

moving on, do we have a schematic to isolate the psu section?

[kaboom]

Re: CRT monitor gone AWOL(please help)

BTW, you have to discharge it more than once.

Yes you do! Dielectric absorption.

It's also a very good capacitor- just rubbing the front of a disconnected CRT with a towel, in dry weather, can charge them up a little.

I've always discharged the anode to the DAG GND. Never blew diodes in the multiplier/rectifier or focus/screen block.

[budm]

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.

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...

i dont know how it damages diodes, i just know it can because i'v seen it.

the 2-screwdriver or crewdriver & wire with crock-clip trick goes back to b/w and probably valve days.
it was always a bodge for people without a high-voltage probe.

That is funny, I worked on thousands of CRT TVs (100% tube and SS) and CRT monitors in my life time. RCA, ZENITH, PHILCO, MAGNAVOX, QUASAR, CURTIS MATHIS, SONY, PANASONIC, MITSUBISHI, WELL-GARDNER, JVC, iiYAMA, NEC, Viewsonic, KDS, etc. and never once damage the Voltage multiplier on the FBT.
RCA supplied us Plexiglass rod with sharp metal tip at the end which attached to the drain ground wire with alligator clip at the end.
It is just B.S. to me. It is funny to hear these kind of stuff from younger generation.
No you did not miss anything.
It is like saying you will damage the rectifier when you discharge the filter caps in the power supply, it is just high Voltage power supply.
Do you damage the rectifier when you discharge the filter caps? NOPE! CRT is just a big high Voltage cap.
BTW, you have to discharge it more than once.

[stj]

Re: CRT monitor gone AWOL(please help)

i dont know how it damages diodes, i just know it can because i'v seen it.

the 2-screwdriver or crewdriver & wire with crock-clip trick goes back to b/w and probably valve days.
it was always a bodge for people without a high-voltage probe.

[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...

[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.

[TechGeek]

Re: CRT monitor gone AWOL(please help)

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

[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)

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?

[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!!

[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?

[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)

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)

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)

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)

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?