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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Magnavox rear projection TV RK8530AK02 - startup problems
Hi there!
I'm working on a Magnavox RK8530AK02 rear projection TV which has a startup problem. The previous owner complained that the set would intermittently fail to respond to the power button in an attempt to switch the set on, whether with the momentary switch on the console or with the remote. This intermittent behaviour gradually became worse. Other than that, there were no other problems (no HV shutdown, no problems with picture, no problems powering off, etc). Symptom has worsened to the point that the set cannot be powered on. No audible noises are heard and no apparent voltage drops on the main board when power switch is pressed. Contacts are good on power switch, line fuse is good, 120V AC is good from primary transformer board to MAIN BOARD and to PTV HV POWER SUPPLY board. Lithium backup battery on microcontroller is good (+3V). No shorted electrolytic caps. I read an archived post about this set whose owner was having the same problems as I am having now. From a reply: ---begin quote--- From: Bill J ) Subject: phil/magn. 45" RP wont turn on....why? Newsgroups: sci.electronics.repair Date: 2000/04/12 First thing to do is with the set plugged in check Tp12 for approx 9 volts. If low (5-6 volts) change C431,C460,C461. Also resolder connections on IC305 (5 volt regulator). If Tp12 has 8.5-9 volts then proceed to turn on the set and check Tp13. Should be 12.5-13.5 volts. If not then replace C450 and C455. One or both of these steps should get the set working. If not then post further info and help will be forthcoming. Bill J ---end quote--- On the main board, voltage on TP12 was -16.5 V; on TP13 was +120 mV (near zero). These voltages were read using tuner shield as ground. I resoldered IC305, which did appear to have a cracked joint, but this did not fix the problem. I have not yet replaced the main B+ filter cap, and having neither an ESR meter nor a scope, I cannot test its functionality. I would appreciate it if anyone who has information on this set could reply with any pointers. Thanks for looking! -- Please remove the word "SPLAT" from either below address to use it. Email: Visit ToasterKingdom at http://SPLATtoasterking.tripod.com/ |
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