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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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Toshiba CF3054J, TAC 8950 Tuner Problems
Channel up/down & higher channels inoperative
A double whammy, but are they related? Problem 1: Some months ago, following a nearby lightning strike which took out the electricity, and undoubtedly induced some "extra potential", the channel up/down and retune (prev chan) functions became inoperative. Channels can be selected and the current channel recalled via the remote control. My chief suspect is the main board circuitry associated with the TMP47C634N2454 microprocessor, ICA01 (p/n 23318860). Since other chip functions seem to work, I question if the IC itself is bad. Another possibility might be ICA02, the M6M80011L memory chip (pn 23318861), which I am guessing holds the preset and recall functions which may be necessary for next and previous channels. Given the age of the set, the tuner inconvenience was bearable, since picture and audio performance are as good as they have ever been. A couple of years back a general recapping in conjunction with the well-known fused R327 resistor problem restored the unit to like new performance. Problem 2. Yesterday, within a period of 5 minutes, both audio and video on the upper channels deteriorated to the point of complete loss on channels 49 and higher. Following a lengthy cool down period with power off, the higher channels are perfect and then in 3-4 minutes suddenly drop video and audio with a loud schrunch. The lower channels 2-48 work perfectly. My first suspect is the EL811Lx1 VHF/UHF tuner module, (pn 23121639)but I question why the lower channels continue to function so well. I am reluctant to replace the tuner, pretty much a cross-the-Rubicon action, as well as time consuming and expensive, without a better understanding of the problem. I am wondering if someone has experienced this before, or at least may have some other leads to investigate. A scan of Toshiba tuner problems seem to suggest failed solder joints, but I wonder why that would affect only channels above 48. I am less inclined to suspect the SIF/PIF board, however, I am wondering if the microprocessor input to the tuner may be at fault, linking both difficulties. Any thoughts on the matter would be much appreciated. Dave Allen Falls Church, VA daveatallencitycom |
#2
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Toshiba CF3054J, TAC 8950 Tuner Problems
More than likely you have to try the tuner module. It is possible to have
one group of channels working, and not another. There are a number of independent front end circuits for the different bands. The tuner is critical and not easy to service. It is normally changed as a complete module, unless the fault is simple. It is rare that the uPC section will give faults for this type of problem that you are describing. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= wrote in message ... Channel up/down & higher channels inoperative A double whammy, but are they related? Problem 1: Some months ago, following a nearby lightning strike which took out the electricity, and undoubtedly induced some "extra potential", the channel up/down and retune (prev chan) functions became inoperative. Channels can be selected and the current channel recalled via the remote control. My chief suspect is the main board circuitry associated with the TMP47C634N2454 microprocessor, ICA01 (p/n 23318860). Since other chip functions seem to work, I question if the IC itself is bad. Another possibility might be ICA02, the M6M80011L memory chip (pn 23318861), which I am guessing holds the preset and recall functions which may be necessary for next and previous channels. Given the age of the set, the tuner inconvenience was bearable, since picture and audio performance are as good as they have ever been. A couple of years back a general recapping in conjunction with the well-known fused R327 resistor problem restored the unit to like new performance. Problem 2. Yesterday, within a period of 5 minutes, both audio and video on the upper channels deteriorated to the point of complete loss on channels 49 and higher. Following a lengthy cool down period with power off, the higher channels are perfect and then in 3-4 minutes suddenly drop video and audio with a loud schrunch. The lower channels 2-48 work perfectly. My first suspect is the EL811Lx1 VHF/UHF tuner module, (pn 23121639)but I question why the lower channels continue to function so well. I am reluctant to replace the tuner, pretty much a cross-the-Rubicon action, as well as time consuming and expensive, without a better understanding of the problem. I am wondering if someone has experienced this before, or at least may have some other leads to investigate. A scan of Toshiba tuner problems seem to suggest failed solder joints, but I wonder why that would affect only channels above 48. I am less inclined to suspect the SIF/PIF board, however, I am wondering if the microprocessor input to the tuner may be at fault, linking both difficulties. Any thoughts on the matter would be much appreciated. Dave Allen Falls Church, VA daveatallencitycom |
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Toshiba CF3054J, TAC 8950 Tuner Problems
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