Path: news.uiowa.edu!news.physics.uiowa.edu!math.ohio-state.edu!howland.reston.ans.net!news-e2a.gnn.com!newstf01.news.aol.com!newsbf02.news.aol.com!not-for-mail From: rubywand@aol.com (RUBYWAND) Newsgroups: comp.sys.apple2 Subject: Re: Repair Apple IIGS RGB, info wanted Date: 21 Mar 1996 14:56:34 -0500 Organization: America Online, Inc. (1-800-827-6364) Lines: 80 Sender: root@newsbf02.news.aol.com Message-ID: <4isc9i$5ia@newsbf02.news.aol.com> References: <4ip4pc$buj@madeline.INS.CWRU.Edu> NNTP-Posting-Host: newsbf02.mail.aol.com X-Newsreader: AOL Offline Reader Monitor Repair Mini-Manual (mostly from stuff in COMPUTIST) First, be safe. (See safety stuff at end.) Mainly, unplug the monitor and let sit for a day, wear goggles, work on non-conductive table surface, do not stress CRT neck. 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. 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. For all 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). Arcing from the metal brace to the HV module can cause the display to momentarily shrink and flick out of focus. 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 is 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. _____ Safety 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. 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. 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. 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. Rubywand "Frank Townsend" wrote in message news:sVxW8.5909$I02.5031@nwrddc04.gnilink.net... > I've had a setback in my Apple II and other computer endeavors: my > venerable NEC 6FGP monitor is on the fritz. The way this relates to Apple > II is that this monitor has both D-sub and BNC connectors and a switch so > that I can use it with my PC and Mac LCIII/Apple IIe card set up. > > The screen image is squashed in the vertical dimension to about 25% of the > usual screen size. > Well... problems with the vertical ckt are easier to fix than problems with the horizontal. The vertical sweep is usually generated by a chip that has a built-in heat sink. Usually just a piece of sheetmetal. It may be mounted on another heatsink. It typically has distinctive "zip" pins, i.e. staggered coming out the edge of the chip. Probably 16 or 18 pins, something like that. Besides the vertical output, it often has sync circuitry on it. There are 4 wires coming out of the yoke, which is a coil on the neck of the CRT. Two of them carry the horizontal sweep signal, and two carry the vertical sweep. So the vertical chip is usually near where those wires connect to the PC bd. Your problem is likely to be that chip, or possibly a power supply problem with a voltage that chip needs. Could also be a bad capacitor. Come to think of it, that's likely. What I often do is get the part number off the vertical chip, look up the diagram for it, and it shows the pinout. It usually has a pin that a capacitor is connected to, which determines the sweep rate. I also try "Technician in a Can", which is what we call freeze spray. Spritz the chip and local capacitors a bit and watch the screen, see if the vertical size changes when you spritz (obviously you have to do that while it's on.) Figure out which part is causing the change and replace it. That's just generic info, may or may not apply to your NEC. Good luck, and of course be careful. But as long as you stay away from the high voltage (fat wire going to a big cap on the fat part of the CRT) and the power supply area, you should be OK. -Paul