NEC professional 27 inch monitor repair

[optimus prime]

Hi all,
This is my first post. I have a 27 inch NEC professional crt monitor that I was going to use in a MAME arcade cabinet for my nephews. I picked it up on craigslist for free because it doesn't work. The unit powers on and seems like it starts to build energy for a picture, but then there is a "click" and nothing happens on the screen. The monitor stays on, with the front light lit and the speakers working (it has built in speakers), but there is no picture (the screen isn't on at all actually so its not an input problem). It doesn't matter which input it is on, I always have the same outcome. I have very limited electronics background and I know you can get really hurt working on a CRT, so I didnt want to tinker around with it. Just trying to get some advice on which way I should go. It's a really cool unit with VGA inputs for dreamcast HD gaming. Would hate to throw it in the trash and I don't want to pay $100s of dollars to have it repaired. The model number is PG-2710. I searched the web and came up with very little on this particular model, however it resembles the one listed on this page very closely http://wolfsoft.de/wordpress/?p=422. The web page has the service manual attached. Any help would be greatly appreciated.

 

[davenn]

hi
welcome to the forums
before we start ... what is your electronics knowledge/experience ?
this could be an involved repair project

cheers
Dave

 

[optimus prime]

I am a handy type of guy and a "do it yourselfer" but my electronics knowledge is pretty limited. I know how to check for voltage, solder wires... things like that. However, I don't know how to read schematics or understand how capacitors/transitors and such work. I was hoping that the description of what is happening would lead one of you electronics gurus to say, "oh that's going to be such and such capacitor on such and such board and it will look like this". I opened the back of the Monitor and it looks pretty daunting in there. I may be in over my head.

 

[(*steve*)]

Large CRT monitors have very high voltages inside (think 10's of thousands of volts). We don't know what might be wrong yet, but you need to keep well clear of the EHT.

Along with the EHT, there will be normal high voltages and mains voltages.

You need to be very careful and also be aware that the danger doesn't stop when you turn it off and unplug it.

The word "daunting" is a good one.

 

[dude]

Insofar as CRT monitor circuit complexity, computer monitors are the most complex and aside from the dangers involved in working on them, not something for a noob monitor/tv technician even. Your monitor is pretty much a state of the art design for what it is at that. Most faults are power supply related, they start by circuit over-voltage which over time leads to a chain reaction of component failures. Once you have found and replaced the blown components you then have to address the power supply and repair that, otherwise it will run for a day, week, month... and then come back to haunt you. Your monitor has fault protection built in, it will shut itself off (usually) before anything blows up spectacularly or over-voltage on the screen causes x-ray emissions to exceed of what the internal paint and shields can block. Give it to someone who knows what they are doing and expect to pay from $150 upward for the repair.

 

[dude]

Large CRT monitors have very high voltages inside (think 10's of thousands of volts). We don't know what might be wrong yet, but you need to keep well clear of the EHT.

Along with the EHT, there will be normal high voltages and mains voltages.

You need to be very careful and also be aware that the danger doesn't stop when you turn it off and unplug it.

The word "daunting" is a good one.

This is kinda a funny story looking back on it, though at the time I felt like adding to the damage. The guy should have known better as he had already been told how to handle, or not to handle CRT tubes.

At the time I was working at this place that used to manufacture equipment with CRT monitors on them and we had a stack of them coming off the line being packaged up for the truck that was on its way pick them up and we were behind schedule. One of the machines had a fault and had been partly disassembled by the assembly crew so that I could find the problem. Anyway it didn't take me long to find the fault but when I looked around for the tube there was no tube to be seen, someone had obviously taken it to put in another machine rather than walk to the store and pick up another one. I asked the apprentice noob that had been with me to go get another one and while he went his merry way I decided to go around the back for a smoke figuring he'd take at least 10 minutes to do so. While I'm standing there having my smoke I see the noob coming back from the store carrying the tube rather awkwardly. I stubbed out my smoke and started walking over to grab it off him but before I could get to him he had shifted his hold and put his hand right over the anode. A scream and the tube goes flying into the air and back down to smash on top of his feet with glass going in all directions and this guy jumping up and down from the new pain now at his feet. It was of course left to me to explain it all away to the manager. The noob turned out to be quite a good technician in the end and he never put his hands on an anode again that I know of

 

[(*steve*)]

I've been considering getting one of these:

I plan on putting it in a glass case with the caption "If you need this then reconsider what you're doing"

 

[dude]

Yes working with those sort of voltages certainly has its hazards. It's usually the inexperienced that will get zapped the most even when they have been made aware which areas to keep their fingers away from as they are nervous and due that distracted. You have to get over the fear factor and it helps to be working with someone that is experienced as you build up your confidence. Having said that, its no guarantee that you won't ever get a zap, I've burned holes in my finger to the bone and yes it was my fault. It's usually a combination of factors that adds up to an accident, tiredness, pressure in getting a job out, general distractions, cramped working conditions, faulty test equipment etc etc. If you use a hammer long enough, you will one day bang your thumb. I'm sure there isn't anyone on this forum that has been through the traps that hasn't at one point given themselves a good jolt, whether in KV range or lower.

 

[optimus prime]

So I decided to take the safe route and take it to a repair man. It was difficult to find someone here in the US to work on an old heavy monitor without charging a huge amount. I will post back with his findings to see if it is worth it or not. Thanks alot for the help.

 

[dude]

Good choice. There are easier things to bust one's chops on then on a monitor like that if you're eager to learn, which it sounds like you are

 

[dude]

I thought I might quickly cover another hazard of working with high voltage stuff, something that might not happen all too often, but can happen, and once it happens to you will add another bit of experience to avoid possible injury, and that is - exploding electrolytic capacitors. I can guarantee to you that if you are close by the equipment when this happens you will jump a foot in the air
What happens is that the faulty capacitor does not vent itself of the gasses it builds up, either by cracking at the top or by leaking through the rubber plug at the bottom. What can happen then is that it builds up enough pressure to act like a firearms cartridge, the can becoming the bullet. When it explodes the aluminum can easily have enough force to put a dent in your ceiling if the equipment's cover is open, if not, you will hear it hit the insides and then rattle around for a bit. When you first see a board where this has already happened you will probably be first stumped for a few seconds by the strange looking component on the board, two wires with tabs attached to them, sticking straight out. If you don't tick straight away you will when you find the can lying around somewhere. The area around the blown cap will be covered with a brown coarse dust. I have never actually found a single piece of aluminum, I can only assume that the aluminum strip vaporizes as it explodes and shorts out.
So... never look a high voltage electrolytic capacitors "down the barrel" when equipment is powered up if you can avoid that, admire them from the sides as they could easily take out an eye