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Path: blue.weeg.uiowa.edu!news.uiowa.edu!uunet!news.mathworks.com!udel!gatech!howland.reston.ans.net!news.sprintlink.net!news.infi.net!larry!dynasor From: dynasor@infi.net (Dennis McClain-Furmanski) Newsgroups: comp.sys.apple2 Subject: Monitor Repair: Dark, Blurry Date: 7 Feb 1995 00:48:01 GMT Organization: InfiNet Lines: 192 Message-ID: <3h6g01$cke@lucy.infi.net> NNTP-Posting-Host: larry.infi.net X-Newsreader: TIN [version 1.2 PL2] Got a request to post this, so enjoy. E-mail me if you have questions. And be careful in there! ===== Disclaimer: I have almost 30 years experience working on this type of device. I know how to be careful when doing these things. You probably don't have this much experience. I will do my best to explain this clearly and in enough detail that you can do it yourself. However, I make no promises, and I certainly do not take any responsibility for the results. If this is a problem, the course is simple: don't do it. This instruction set is offered to the public domain and may be passed around or reprinted anywhere, so that others may benefit. I only ask that you leave my name on it. Dennis McClain-Furmanski, dynasor@infi.net. GS MONITOR REPAIR -- HIGH VOLTAGE PROBLEMS This is a set of instructions for repairing the GS monitor. This is not hard, but it is not without difficulties or danger. Please pay very close attention to both instructions and caution warnings. Read it all at least twice before trying to do anything. Make sure all power is off before connecting or disconnecting anything to the computer. The GS monitor, just like all other high voltage driven CRT devices deteriorates in function with age. This is unavoidable wear-and-tear, and is accounted for in the design. The problem is deterioration in the high voltage circuitry and/or those portions on the monitor which are operated by it. SYMPTOMS: Increasing loss of brightness, contrast and/or focus. The picture may 'bloom', that is get larger when you turn up the brightness, and shrink when you turn it down. Associated side-effects: flashing and/or inconsistent brightness fluctuation while trying to adjust the external brightness and contrast controls. PROBLEM: Primarily in the high voltage transformer. This 'fires' the electron guns, which produce the raster. This is adjustable up to a point. The side-effects are dirty controls; they can be cleaned. THE FIX: The easy one first -- even if it's not necessary, you might as well do it while you're in there. Clean the brightness and contrast controls. DISCONNECT THE MONITOR FROM THE COMPUTER AND FROM THE WALL. For safety's sake, I suggest doing this a day or two before working on it. Open the GS monitor by removing the four screws, two on the back of the top 'flange' around the screen, two on the bottom facing the front, in the long 'channels'. Slide the back off of the monitor slowly, until the edge of the back is even with the back edge of the motherboard, the circuit board on the bottom of the monitor. Feed the power cord through the hole in the back as you slide it off. The wires leading to the controls on the side of the monitor might hang up. If so, simply loosen them and continue. Once the back is free of the chassis, slowly slide the back towards the right side (as you face the front) of the monitor. This is so you don't put strain on the wires going to the controls on the side. Look inside the back, at the controls. The power switch, brightness and contrast controls are all mounted on the inside of the back. You can clean the brightness and contrast controls, to alleviate the flashing or inconsistent response. Using a pencil, mark the controls and the case so that you can set the controls back where they were before you started messing with them. Get a spray can of NON-ABRASIVE contact cleaner. (This is probably al you'll find; the abrasive type was mostly for the old mechanical channel changer-tuners, but make sure). Make sure it won't hurt plastic. It will say so on the can. Try to get a can with a straw that fits into the spray cap. Spray some into one of the two controls, and turn it up and down repeatedly. Do this a few times. Then do the other control. Allow these to dry completely before you try to fire up the CRT. If this doesn't fix this problem, it's likely these will need to be replaced. The parts look to be fairly common. Sorry, I don't have details on them, so you'll have to get help with this. Now to attack the main problem. Look at the body of the CRT (picture tube). There's a big fat red (usually) wire coming out of it to the right of the long 'neck' of the tube (looking from the rear now). This is the high voltage wire. In fact, it's the VERY high voltage wire. There's enough juice in this thing when operating to knock you down and possibly kill you. Even when turned off, enough can be stored in this area to really bite you. This is why I suggest waiting a day or two before messing with this. It gives the power time to drain off. This big wire goes into the top of a plastic device which is partially covered with a metal cage. This is the high voltage transformer. Facing the rear, you will see two small adjustment stems, one above the other. The upper one is marked FOCUS, the lower one SCREEN. This is on the collar around the stem. If your problem is increasing darkness, the SCREEN control is the one you'll want to work with mostly. If your display is out of focus, obviously you'll work with the focus control. In either case, you may have to adjust both of them somewhat. Before you do anything else, MARK THEM. Use a pencil, and mark the control and the body of the transformer so you can set things back the way they were in case you get too messed up. Now stop and think. The rest requires adjusting the high voltage controls (THOUSANDS of volts) with the set turned on. This is DANGEROUS. If this bother you, reassemble it now and do not go any farther. Take it to a tech. They should be able to do the rest of this for a minimum labor charge. Want to continue? OK, let's go. Set up the monitor with the back still off and slid to the side, and connect both the power and the signal cable from the computer. Set it up so that you can work with plenty of room to move around the back. Set up a mirror in front of the screen, so you can see what's going on with the picture while you make adjustments without having to crane around to look at the screen. This would cause you to be in a position where you are not able to see your hands while working, and this is the best way to get bit. DO NOT, under ANY CIRCUMSTANCES try to work on anything without being able to see your hands. Now, fire it up, and give yourself a familiar screen such as Finder, ProSel menu, whatever. Adjust the mirror so you can see the screen clearly from behind the monitor. Make sure your brightness and contrast controls are set back where they were before you cleaned them. Now, using a plastic handled, if not *entirely* plastic, screwdriver, slowly adjust the control on the back of the transformer. KEEP AN EYE ON YOUR HANDS. Do not come into contact with anything other than the tool handle. Watch the mirror for changes in the picture. Adjust SCREEN first if the problem is mostly brightness. Adjust FOCUS if the picture is fuzzy. Adjust them both as necessary to obtain the best picture. You may want to adjust the brightness and contrast controls down while doing this, because you may have over time moved them up to compensate for deterioration. Try to get them in the middle of their range, with the picture at your preferred viewing brightness. If you can get things set the way you like it, great. Now try testing it while it's still operating. Adjust the brightness control on the side up and down. If you still get 'blooming', the transformer is going bad and will need to be replaced. It will probably cost more than the monitor is worth. Ask a tech how much to change your Hi-V transformer, and decide. If no matter what you do with the FOCUS, you still get a fuzzy picture, your CRT is probably 'gassy', that is losing vacuum. This is definitely more costly to replace than to get a new one, unless you can get a tube from another monitor and replace it yourself. Once you have things where you want them, turn it all off, disconnect everything, and reassemble the monitor. Your repair job is done. If it worked, you just saved yourself somewhere between $50 and $150. If the brightness still does not come up enough, there's one more thing that can be tried. The electron guns can be 'burned off', that is hooked up to a tube tester which can put a great deal of voltage through the guns and burn off any oxides on the gun filaments. This must be done by someone with this device, in other words a tech. This is at best a temporary fix, and is equivalent to the "picture tube brighteners" you can purchase. If this needs to be done, you're working with a limited lifetime on the tube as is, and doing this may well shorten that lifetime. Any questions, or anything not clear about these instructions, write me and I'll clarify. -- dynasor@infi.net The Doctor is on.