Voltage Probe
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Voltage Probe
How To Repair Acer AJ17 Monitor With Display Big Problem
This Acer AJ17 Monitor came in with the complaint of wide screen and distortion (line swimming) across the vertical line of the display. Although you can adjust the horizontal size, you just can’t make it into smaller and the horizontal size still big and curve inward. You could also clearly see all the vertical lines at the display have a small wave (distortion) across it. At first I thought it was caused by a defective filter capacitor at secondary side of the display but all the capacitors checked to be okay.
Since all the caps tested okay, now I fully concentrate on the horizontal size and pincushion circuit area. If there are any components shorted or faulty in this area, it will cause the display to go big (wide) and many times you can’t tune it back to normal size. From experienced, mostly the problem was the modulation diode that have shorted or a pincushion transistor that have leaked. But both components and all the nearby circuit components checked to be okay too. Using high voltage probe to test on the anode voltage proved it to within the right range. For your information, if the holddown or safety capacitor capacitance value out it could also cause the display to turn big but of course the high voltage measured at the anode cap would be higher.
Since all the suspected components measured okay, I would then use voltage testing to locate the fault. Just before doing the voltage test, I observed that the eeprom ic is installed just beneath the picture tube. If any eeprom ic in any monitor located under the belly of the CRT, then chances are high the data would be corrupted by the discharge of the CRT.
If you repair some of the latest model of Samsung Monitor, you will understand why because the Samsung monitor had a piece of aluminum shielding to protect the microprocessor and eeprom IC from being discharge onto it. A corrupted eeprom data could cause the micro processor to output a wrong signal to certain or all circuit. If it send a wrong signal to the DPMS circuit, then the monitor will shutdown once the power is on.
The ACER AJ17 eeprom IC part number was 24C08. I used to keep good eeprom data in my hardisk for future use just in case if there is a need to reprogram the eeprom IC. I took out the eeprom IC from the board and insert it to the center socket of the pony prog eeprom serial programmer. I then connect it to the serial port of my computer and begin to look for the good data for this model. I do keep a lot of ACER monitor eeprom IC data. Once I got it, I overwrite the old data with the good data.
Installing back the eeprom IC took only a while and the Monitor was switched “on”. Guess what? Not only the horizontal size now got back to normal, the distortion at the vertical lines vanished too. You better believe it that a corrupted eeprom IC could cause many weird symptoms. For some monitors, once the eeprom IC have been programmed, although the monitor work, the color may run. Some techs are good in changing the code in the data and tune to the desire colors.
In order to make the new reprogrammed eeprom data last longer, you can add a piece of shielding on top of the EEprom IC to prevent any loss data in the future. Bare in mind that, eeprom data loss not only occurs in monitor, it could happen in other electronic equipment too such as LCD Monitor, Television, UPS and etc. Whether you are repairing the ACER AJ17 or any other brand of Monitors, if you come across any weird problems that you can’t solve, try reprogramming the eeprom IC and who knows the monitor may work again. In order to do this, of course you need a serial programmer which you can easily buy one from the internet.
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Learn Electronic Component Testing.
measuring voltage, which probe goes on the cathode which goes on anode?
doing a lemon battery experiment..
If you mean cathode as the place where the reduction takes place, you connect the positive end of the voltmeter to this and the negative end to the cathode.
If your voltmeter is color coded, the black wire will connect to the anode and the red one to the cathode.
NI Multisim: Measure voltage with a referenced measurement probe
