Computer Monitor Troubleshooting And Repair Pdf MacNotes on the Troubleshooting and Repair of Small Switchmode Power. Supplies 1. 99. 4- 2. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the. This notice is included in its entirety at the beginning. There is no charge except to cover the costs of copying. If an ESR meter is available, test. When the shunt regulator kicks in, the. LED turns on reducing the switchmode transistor drive. Use clip leads or solder temporary wires to reach cramped. ![]() I built. a dual outlet box with the outlets wired in series so that a lamp. The unused low voltage. It's handy for quick checks of semiconductor junctions - . ![]() B/E. junctions have an inherent zener voltage, so there is usually some glow. Any zener diode above 1. V can be given a quick test for S/C. Vz will produce some glow - again check Vf before binning. Some Automotive accessory shops have a simpler version. AC or DC at 4 to 3. Computer Monitor Troubleshooting And Repair Pdf CorruptedV before parting with money! The internal circuit should. LED's, a 1. 5 ohm resistor to limit the maximum surge current when. PTC is cold and the special PTC film- thermistor. The battery can be. VCR front panel - but don't blame me if you kill. ![]() There is. a more complicated non- battery version with 2 LED's close to the front of. LED's along the length of the. This version contains 2 special PTC's. As for the special PTC this is the only place I've. Troubleshooting computers is like solving the problems you solve in everyday life. Once you understand the basic structure, you can easily determine where the problem. ASUS Support Center helps you to downloads Drivers, Manuals, Firmware, Software; find FAQ and how-to guides, step-by-step set up and installation. Don't just sit there scratching your head, find useful info on PC Support on eHow. Get essential tips and learn more about everything from How to Change the. View and Download Philips 220P2 troubleshooting manual online. Philips LCD Monitor User Manual. 220P2 Monitor pdf manual download. ![]() Siemens PTC SMPSU startup thermistor for TDA4. European TV set's, but I have seen it in early Matsushita IBM displays and a. Tandon) the PTC thermistor is always blue and looks. Philips white- plastic PTC degauss. While I am not criticising the use of. I tend to find that these get tidied away, so. My bench. isn't the tidiest in the world, so gadgets tend to get misplaced - including. LED indicators. This is where. NTC comes into it's own, even without selecting the. Obviously the energy causes some heating - . These items can be salvaged from a scrap monitor or. PSU, and careful selection may reveal some types with a . This reduces the welding- sputter as the contact current is only a few. Most SMPSU's of any appreciable power have high energy. In the case of monitors, the post PWM- B+ rail has a large. The NTC thermistor method. As well as the suggested use to limit inrush. SMPSU boxes - I also use this method on line- O/P. B+PWM or SMPSU blow- up. Recently I have been caught- out a. The UK. 2. 20/2. 30 V 6. W test lamp I have here has a calculated operating resistance of. PTC effect of the filament tends to limit the advantage! In any event - bypassing the B+PWM MOSFET via. More recently, the trend has been for flyback - step up B+. When the B+ MOSFET fails S/C it simply stalls the main SMPSU. Since this type of B+PWM is step- up. S/C MOSFET. The most recent designs appear to be based on semi- resonant. SMPSU topology - they resemble buck- regulator PWM controllers, but the PWM. MOSFET is at chassis potential and the transformer primary is at full. PSU- rail, the line- O/P transistor is between the two with the drive. The boost diode often. As the later configuration most closely. When. this checker is used around SMPSU's, you can clearly see the effect of. Vf well in excess of 0. V. for the minority carrier injection delay - before the rectifier begins to. Where a PSU rectifier has two electrolytics and a choke in a Pi. ESR failure. There would likely be no output at all. With a decreasing. A. hysteresis current. The oscillator inside the 3. V on Vcc and stops working when this voltage drops below 1. V. So the oscillator can't continue to work with only the startup. First, the. 3. 84. A, Vcc reaches 1. V, and the oscillator starts up. If. all is well (no overloads), the transformer provides the necessary 1. A. current to maintain Vcc at more than 1. V. The Pic. Tel. has a big Onan switchmode PSU which is autoswitching between 1. It got confused, and (regrettably) chose the former.. That's. obvious since pushing on the cover will soften the hum. The frequency is. Hz or 1. 20. Hz. It may also indicate a PC type power supply that's overloaded. Sometimes the pitch of. If they're not wound tightly and secured they. Many video monitors exhibit this problem when their flyback. It may be the windings themselves moving or. Caps in SMPS'. frequently have high AC current levels. If the supply is supposed to have. Since the SMPS will go. Hz, it's audible. I've. run into this on breadboards I've built for 2. W and 2. 5k. W SMPS'. Stessen (Jeroen. Stessen@philips. Electrolytic capacitors like to be kept cool! It causes them to dry out. The latter are obviously more temperature resistant. Caution is advised, as low. ESR caps will not limit surge currents. As the DC. voltage from the external PSU is increased to the value of what the SMPS. PWM waveform can be. It depends on the design. The problem is manufacturers. They should tell you if it will. Secondly they should tell you what. The SMPS hot side is a high frequency oscillator whose 'on time' is. The troubleshooting. Trace the bias supplied by the. Then remove one leg of the output. Don't forget to check the voltages and waveforms in your. Noisy (whining or buzzing) SMPSs that still work tend to be either bad. The transformer has a +5 V. It also has a +1. V output and a - 1. V. output. All transformer outputs are related in voltage by the transformer. The power supply topology is a Half Bridge, which normally. To vastly improve the cross regulation between windings, a common. So the thing is basically a 2. Volt design. This means that in order to start, there must already be an output. How they do this is really really clever, and also extremely. The power transformer is itself, self oscillating. This generates. a rudimentary output voltage that allows the thing to bootstrap up to normal. This is done to eliminate the need for troublesome. To boot itself up (after all, there is no initial +1. V. to allow itself to start), the driver transformer is modified (very cleverly). Thus the unit initially self oscillates. V output to allow. PWM to start, which then swamps out the self oscillation and normal. These are far and few between and sign non. Many PC power supplies aren't. Compaq, Elonex, HP, Apple, Sun etc that are. Also in many countries a swap out isn't available or can be costly. The same type of. Older power supplies often used the TL4. C pwm IC. newer use the UC3. MOSFETs. Some older still used the. NE5. 56. 0, SG3. 52. PWM IC, but instead discrete. Data sheets on the IC's used are very useful. A winding. on the secondary supplies a voltage that is rectified and smoothed to feed. PWM IC and its drivers. These then drive the 2 transistors via a. The 5 V output voltage is then. PWM IC to maintain regulation. Secondary rectifiers can fail, and electrolytic caps can. The PWM circuitry can always be fed with an external. DC supply and checked independently. This IC sits on the primary. An isolating transformer is needed. If you are going to be repairing a lot of varying. This is basically banks of 2. N3. 05. 5's (for 5. V & 3. 3. V) and 2. N3. 77. 3 (for. 1. V upwards) in series with low value power resistors than can have their. You simply have. a lead for each power supply type you test/repair. Also don't forget to. PG o/p on the power supply. This color of that wire is mostly. If you look on top of the ATX. ATX connector is often depicted there with pins labeled. Check. the label on the supply and load the main +5. V and +1. 2 V line to about. Well that list is long and still does. If not, power supply controller. It follows. below and should contain all you need (and more) to decide whether your power. After replacing. this fuse, connect the PS to the mains using the series light bulb trick. The first thing. you have to do now is to find the short circuit. The most suspected. Use eyes, nose and an ohmmeter. Remove and check the suspected. Replace defective components except for the power. It makes no sense to continue until you fixed. If the fuse is good but the PS still dead, you can start to check the. I call it the primary power. The midpoint. should be at half the primary power voltage. You can recognize the pair of transistors best by finding the. You can check this with an AC voltmeter. The reading will not be correct. AC voltage you have to continue checking the. Most of the times you will have to provide a new. Even a transistor that looks good under test conditions. This is also the time to remove, check and replace other fried, exploded or. You have to dive deeper into this part of the. Finding +5 VDC, you can. This is simply because of some PSs will not function. You may use an (old) main board. Someone ever told me he. V car bulbs, one on the +5 VDC and another on the +1. VDC outputs. I. prefer a huge and heavy old harddrive. Those old basalt blocks (we use to. The one I use, provided. PSs I ever repaired. Check the. voltage between pin 3 and pin 9 of the main board connector. Connect pin 1. 4. This will switch on the main part of. PS, the part with the two power transistors and the large transformer. When they have the correct values your PS is on air again. You have to investigate the. Most. likely your power transistors are gone so you have to check (and almost. When you. are done, restart at Step 1. A fault on the secondary side of. Disconnect from the. You will have to remove the rectifiers. Another trick is to use a controllable. Connect it to the point where the removed rectifier was. Beware of the polarity! Power on both. PSs and increase the voltage of your controllable PS to the level of normal. PS. The regulator that sucks to much current. The collector of one of. The remaining collector and emitter are tied. Maybe a bad soldering or the like. Restart. at Step 1. If they are. less than 0. V you may be lucky and find only defective start resistor(s). But most of the times a defective base. The control IC for. Oh, and there's a current- limit shutdown from a 0. R1. 5. resistor in series with the 'load' (section 3, etc). The output of this. V. The output of that feeds a pair of transistors that run as a free- running. That drives the primary of the main chopper.
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