Path: news1.icaen!news.uiowa.edu!chi-news.cic.net!feed1.news.erols.com!howland.erols.net!portc02.blue.aol.com!portc01.blue.aol.com!audrey01.news.aol.com!not-for-mail From: rubywand@aol.com Newsgroups: comp.sys.apple2 Subject: Monitor Repair Mini-Manual Date: 18 Nov 1996 04:26:55 GMT Organization: America Online, Inc. (1-800-827-6364) (1.10) Lines: 300 Sender: news@aol.com Message-ID: <19961118042900.XAA21390@ladder01.news.aol.com> References: <56mslc$t4e@freenet-news.carleton.ca> NNTP-Posting-Host: ladder01.news.aol.com X-Newsreader: AOL Offline Reader Monitor Repair Mini-Manual (This mostly came from COMPUTIST articles. There have been some valuable contributions by csa2 readers, too.) Mainly, this mini-manual relates to fixes which involve removing the case. Before removing the case, check to see that the your problems are not due to a poorly connected monitor cable. Also, try diddling the side and back controls. Sometimes, these become dirty or develop bad spots. If diddling a control cures an unstable, jumping, etc. display, you can be fairly sure that a squirt of Control Cleaner will help. (You will still need to remove the case; but, at least, you will know what to do.) Safety Basically: unplug the monitor and let sit for a day, wear goggles, work on a non-conductive table surface, do not stress CRT neck. Unplugging the monitor and letting it sit for a few hours reduces the danger of shock from stored charges; it does not eliminate it. The usual warning for this kind of work is AVOID touching two different circuit points at the same time. Like, don't touch the metal chassis and the conductive surface of the CRT at the same time. WEAR protective GOGGLES. If you should, somehow, bump or stress the CRT neck-- as in jumping when you get shocked-- it may break. The result may be a peaceful THOOP! or the CRT may implode in a spray of glass. (Avoid using the CRT's neck to support the monitor in any position.) Work on a wooden or plastic-topped table with plenty of space. Try to position yourself, tools, and the monitor so that when you get 'stung', the chances of breaking something are reduced. As much as posible, avoid using heavy tools of any kind. An inadvertant tap from a mini-screwdriver is much less likely to crack the CRT than a bonk from a full-sized screwdriver or pair of pliers. Rubber gloves are probably a good idea so long as they do not get in the way. Of course, pointy connections and components can puncture gloves. It's a good idea to clip a wire to the chassis and touch the other end to the conductive surface of the CRT a few times before doing any work in order to drain off any charge there. Note: Several places in a monitor or TV carry high enough voltages to deliver an uncomfortable shock. Draining the charge from one point does not guarantee that other points have been discharged. Joe Walters contributed some info on Discharging the HV anode ... The HV charge (20,000+ volts) might not be much reduced by just waiting a few hours (or days), especially if you are in a low humidity location and the tube, etc., are all of good quality. 1. There is a long wire (called the anode) that goes from the high voltage power supply to the top of the tube where it is snapped into a hole. You can't see the hole because there is a rubber shield built onto the wire. The end of the wire goes to a metal clip which, without the rubber shield, looks somewhat as below. One squeezes the clip so the end slips into the hole in the tube. --- --- == \ / ===== back of CRT \ / <-- metal clip (This is what your grounded screwdriver needs to touch.) | [|] insulated Anode lead going to HV module [|] Needless to say, UNPLUG the monitor before beginning. Simply turning it off isn't good enough. 2. Get a clip lead and clip one end to a long slender screwdriver 3. Clip the other end to the metal chassis of the TV (i.e the metal frame parts) 4. Carefully! slip the screwdriver tip under the rubber flap on the top of the tube until it touches the internal wire that both holds the anode wire in place and conducts electricity. Step 4 may result in a somewhat loud "SNAP" as the tube is discharged. Be prepared so you don't jump and break something. ============ Opening the Case ... Whatever it is you plan to fix, if you remove the monitor case, you will probably need to unplug the cable running from the circuit board to the Controls/Switch Module on the side of the case. Use 'whiteout', nail polish, etc. to mark the position of the plug. In more detail ... 1. Unplug everything from the monitor & let it sit for a day. 2. Put on protective GOGGLES. Place the unit face down on a wooden or plastic-topped surface with lots of space and good lighting. Remove the the screws. Place the unit in nomal position. 3. Have a fat magazine ready. Slide the case off until you are able to see the control leads plugged into the main board on the right side of the case. Mark the plug position with 'white-out', nail polish, etc.. Unplug the connector. 4. Slide off the case while supporting the monitor and slide the fat magazine under the circuit board to prop up the monitor from behind. 5. Discharge the HV (optional, but, generally, but a good idea). 6. 7. When done, reinstall the control assembly. 8. Still wearing GOGGLES, support the monitor, remove the magazine, slide on the case, reconnect the plug, finish sliding on the case, replace screws. ========================== Soldering For any soldering use a good quality pencil-style iron rated at 25-40 watts with a holder. Use high quality (60/40 or better) rosin core solder (e.g. Kester "44" 20 gauge). ========================== Flickering, Jumping, ... If the monitor exhibits major flickering, periodic collapse of the display to a line, etc., then it may help to know that a common source of such problems is one or more bad connections where the High Voltage module is joined to the main circuit board. (This module is the black thing with a HV lead running to the CRT-- it's near the left, back. The slotted nub controls in its case set Focus and base Intensity.) Often these connections look okay because it is hard to see the small fractures in the solder surrounding the pins. The cure is to resolder all of the pins coming from the module (on the under-side of the circuit board). Before doing the soldering, clip a wire to the metal chassis and touch the other end to each HV module pin and other points in the area. While soldering, avoid touching anything conductive on the monitor with anything but the iron and solder. ========================= All-blue, all-red, etc. screen? You probably have a blown choke on the little chroma board mounted to the back of the CRT. The choke will be connected to one of the larger, R/G/B output transistors. Use an Ohmmeter to find the open choke. Replace the bad choke with 'one like it' or brew your own: wind about 25-30 turns of #30 wire on a small ferrite core. A more detailed procedure is presented below .... 1. The part that causes the problem when it fails is a "choke" or "inductor" , it is mounted on a small circuit board attached to the back of the monitor tube itself. This part looks like a small blue ceramic ball with two leads coming out the bottom, and is color coded for 10 microhenries. 2. There are three of these items on that circuit board, and if any one of them fails, the symptom is a screen all of one color, with total loss of any controls of the monitor. The parts are identified by number, and what color the screen is will tell you which one to replace. L6R2 for a Red screen L6G2 for a Green screen L6B2 for a Blue screen 3. You can probably get a 10 microhenry choke at Radio Shack, or it is available for $1.28 (plus a $5 Handling charge) from Digikey Corporation at (800) 344-4539. They take Mastercard, Visa, and C.O.D. The Digikey part number is M8025-ND. 4. After replacing this part, the monitor colors may need to be readjusted via the small color trimpots on the same circuit board. ============================= RGB Adjustments Info This is what some of the RGB pots are: R13 RGB Intensity C86 Horizontal Position on RGB C85 NTSC Color Hue Adjustment C45 NTSC Frequency Adjustment ============================= Centering Adjustments (from James Poore) Color monitors do vertical and horzontal centering differently than do monochrome monitors. Almost all color monitors have either a jumper arrangement or actual centering controls, sometimes both. If your monitor has a jumper, there should be 3 tabs that the jumper can be connected to. For vertical adjustment the tabs should be marked as 'up', 'down', and center. If your pix is too high, then you would connect the jumper to the down tab. For horizontal adjustment the three tabs should be marked 'left', 'center', and 'right'. If your monitor has centering controls, then adjust for best centering. Also centering controls are usually located on the PCB with no access holes, so the back will most likely have to be removed to get to them. ================================== Adjusting Focus and Intensity on a blurry GS RGB Monitor. These adjustments may also help cure display "bowing", etc.. Intensity and Focus controls are on the High Votage Module (black module near back of circuit board) inside the case. Follow procedure outlined earlier for safety (e.g. unplug, wait, wear goggles, ...) and removing the case. Note the position of the two controls on the HV Module (at the left, back). Mark the back of the cover where handy access hole should be. Take the case cover to another area (i.e. away from the exposed CRT neck). Remove the control assembly from the right side of the case. Using a Dremel tool, hole saw, ... cut an approx. 1" diameter hole in the back of the case. Use this opportunity to give the case interior a good cleaning. (If you wash it, be very sure it's dry before continuing.) Reinstall the control assembly. Put everything back. Reconnect cable and AC cord. Turn on the computer & monitor. Let it sit 10-20 minutes. Use the normal side of case controls to get the brightest, 'decent-focus' picture you can obtain. Using a plastic TV technician's tool (and flashlight if necessary) adjust the Intensity and Focus controls (through the hole in back on the HV module) to get a good looking display. Work back and forth between the back and side controls. What you're aiming for is a display with good brightness and sharp focus when the side controls are near their middle positions. Cover the back hole using a piece of duct tape, a large sticker, etc.. (The opening is a potential shock hazard, especially if the monitor is within reach of children.) ========================== Shrinking, Flicking in-out of Focus, ... Arcing from the metal brace to the HV module can cause the display to momentarily shrink and flick out of focus. Follow safety and setup procedures outlined earlier. The cure is to bend the brace up enough to increase the arc path and clean the surfaces involved. Apply HV dope to the brace and module where distances are small. If the case interior seems pretty clogged with dust and gunk, it's a good idea to remove the side-mounted Controls/Switch Module and give the case a good washing. (Be very sure it is well dried before replacing.) You should also clean the two controls on the C/S Module with spray-in Control Cleaner. Before putting the case back, this may be a good time to adjust base Intensity and Focus (the two nub controls on the HV module). Position the monitor so that screen is easy to see and the nub controls are accessible. Plug in the the C/S Module. Adjust the C/S Module controls to center positions. Plug in the monitor to the computer. Get a Desktop display with some text and icons. Use an insulated tool to adjust the nub Intensity and Focus controls for maximum sharpness at 'normal' viewing intensity. A magnifying glass is helpful to obtain max pixel sharpness. ========================= R/\/\/ Rubywand