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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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#1
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Grundig TV CUC7880 or 7890 intermittent failure to power-up
This (Large screen) TV keeps coming back on my workbench with the label
""DEAD"" Actually it is NOT dead, the LED turns RED when mainpower is applied, but it refuses to accept any REMCO or Front Panel commands. Just letting the set sitting idle for 3 minutes brings back all LIFE to its circuits and it plays as advertised with vivid sound and colours..... Switching it OFF via the REMCO or Front Panel and trying it again to powerup works as one would expect. I.e. perfect within seconds. Pulling the main powercord and leaving the set unpowered for a week or so, brings back the initial failure to switch on properly. Again, just sit and wait for 3 or 4 minutes will restore normal operations. As the Manual for this model does not warn for prolongued warm-up periods I feel that some capacitor(s) has lost it's Farads resulting into this extremely long power-up period required. I checked numerous Caps for ESR but really could not pinpoint the defective circuit. As normal ops always returns in a few minutes I have not much chance to do any scoping and/or probing. Is there any most likely cause of problem or any suggestion to disable one or more protection circuits ? TIA Bram Stolk |
#2
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Sounds like a bad filter cap in the SMPS section..
kip "Bram Stolk" wrote in message ... This (Large screen) TV keeps coming back on my workbench with the label ""DEAD"" Actually it is NOT dead, the LED turns RED when mainpower is applied, but it refuses to accept any REMCO or Front Panel commands. Just letting the set sitting idle for 3 minutes brings back all LIFE to its circuits and it plays as advertised with vivid sound and colours..... Switching it OFF via the REMCO or Front Panel and trying it again to powerup works as one would expect. I.e. perfect within seconds. Pulling the main powercord and leaving the set unpowered for a week or so, brings back the initial failure to switch on properly. Again, just sit and wait for 3 or 4 minutes will restore normal operations. As the Manual for this model does not warn for prolongued warm-up periods I feel that some capacitor(s) has lost it's Farads resulting into this extremely long power-up period required. I checked numerous Caps for ESR but really could not pinpoint the defective circuit. As normal ops always returns in a few minutes I have not much chance to do any scoping and/or probing. Is there any most likely cause of problem or any suggestion to disable one or more protection circuits ? TIA Bram Stolk |
#3
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Kip,
You mean caps at secondary outputs of mainsupply ? There are about 10 high capacity electrolytics in that area which I measured for ESR while in the circuit. Probably a straightforward Remove and Replace with fresh ones might get this set from my bench again (for a while) I am also still suspecting RESET circuits at IC's 810 and 850 in the Control unit, Think i'll hook up some storage/recording eqt at essential I/O's to see whether a certain voltage will transit not nicely from Lo/Hi or vv... When defective component has been isolated and identified I'll let U all know..... TIA Bram Stolk "kip" schreef in bericht .. . Sounds like a bad filter cap in the SMPS section.. kip "Bram Stolk" wrote in message ... This (Large screen) TV keeps coming back on my workbench with the label ""DEAD"" Actually it is NOT dead, the LED turns RED when mainpower is applied, but it refuses to accept any REMCO or Front Panel commands. Just letting the set sitting idle for 3 minutes brings back all LIFE to its circuits and it plays as advertised with vivid sound and colours..... Switching it OFF via the REMCO or Front Panel and trying it again to powerup works as one would expect. I.e. perfect within seconds. Pulling the main powercord and leaving the set unpowered for a week or so, brings back the initial failure to switch on properly. Again, just sit and wait for 3 or 4 minutes will restore normal operations. As the Manual for this model does not warn for prolongued warm-up periods I feel that some capacitor(s) has lost it's Farads resulting into this extremely long power-up period required. I checked numerous Caps for ESR but really could not pinpoint the defective circuit. As normal ops always returns in a few minutes I have not much chance to do any scoping and/or probing. Is there any most likely cause of problem or any suggestion to disable one or more protection circuits ? TIA Bram Stolk |
#4
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Around the SMPS trany...
kip "Bram Stolk" wrote in message ... Kip, You mean caps at secondary outputs of mainsupply ? There are about 10 high capacity electrolytics in that area which I measured for ESR while in the circuit. Probably a straightforward Remove and Replace with fresh ones might get this set from my bench again (for a while) I am also still suspecting RESET circuits at IC's 810 and 850 in the Control unit, Think i'll hook up some storage/recording eqt at essential I/O's to see whether a certain voltage will transit not nicely from Lo/Hi or vv... When defective component has been isolated and identified I'll let U all know..... TIA Bram Stolk "kip" schreef in bericht .. . Sounds like a bad filter cap in the SMPS section.. kip "Bram Stolk" wrote in message ... This (Large screen) TV keeps coming back on my workbench with the label ""DEAD"" Actually it is NOT dead, the LED turns RED when mainpower is applied, but it refuses to accept any REMCO or Front Panel commands. Just letting the set sitting idle for 3 minutes brings back all LIFE to its circuits and it plays as advertised with vivid sound and colours..... Switching it OFF via the REMCO or Front Panel and trying it again to powerup works as one would expect. I.e. perfect within seconds. Pulling the main powercord and leaving the set unpowered for a week or so, brings back the initial failure to switch on properly. Again, just sit and wait for 3 or 4 minutes will restore normal operations. As the Manual for this model does not warn for prolongued warm-up periods I feel that some capacitor(s) has lost it's Farads resulting into this extremely long power-up period required. I checked numerous Caps for ESR but really could not pinpoint the defective circuit. As normal ops always returns in a few minutes I have not much chance to do any scoping and/or probing. Is there any most likely cause of problem or any suggestion to disable one or more protection circuits ? TIA Bram Stolk |
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