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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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Need help on diagnosing TV with bad HO-Stage
Hello,
I have a Lifetec LT-7079VTS television (German no-name brand), which is actually a Schneider TV 9.6 chassis. The problem with the set is that it can be turned on but no raster comes up. The HV is present (electrostatic field) and the filaments are glowing, but as said before no raster. I have tested the LOPT (unsoldered) and its okay (type S2055N). The weird thing is though that Basis and Emitter of the LOPT are shorted (at least for DC) on board so I suppose the LOPT cannot work properly. I have tested a lot of parts as suggested by the EURAS repair-database but all of them are ok. I suppose the horizontal transformer to be bad but I have no idea how to test it. Any ideas ?!? Adrian |
#2
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Need help on diagnosing TV with bad HO-Stage
Hello,
Adrian Glaubitz wrote: Hello, I have a Lifetec LT-7079VTS television (German no-name brand), which is actually a Schneider TV 9.6 chassis. The problem with the set is that it can be turned on but no raster comes up. The HV is present (electrostatic field) and the filaments are glowing, but as said before no raster. I have tested the LOPT (unsoldered) and its okay (type S2055N). The weird thing is though that Basis and Emitter of the LOPT are shorted (at least for DC) on board so I suppose the LOPT cannot work properly. I have tested a lot of parts as suggested by the EURAS repair-database but all of them are ok. I suppose the horizontal transformer to be bad but I have no idea how to test it. Any ideas ?!? Adrian Okey, I got further. The short from emitter to collector is normal and comes from the flyback coils (didn't know that before, read that in the FAQ). I measured the B+ across C and E of the HOT and it reads about 140 Volts. If I turn the screen voltage, I can finally see a raster, but there is still no picture (e.g. noise or OSD). Any hints ? Adrian |
#3
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Need help on diagnosing TV with bad HO-Stage
On 24 jun, 05:05, Adrian Glaubitz
wrote: Hello, I have a Lifetec LT-7079VTS television (German no-name brand), which is actually a Schneider TV 9.6 chassis. The problem with the set is that it can be turned on but no raster comes up. I have no record of the schneider 9.6 chassis. are you sure it is schneider not beko or something? how old is the set? post some jpegs on fileden.com or you send it and we can try and give more specific help. fault: likely open resistor or bad cap in the RGB stage. star on CRT neck pcb and trace it back from there. -b |
#4
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Need help on diagnosing TV with bad HO-Stage
"b" wrote in message ... On 24 jun, 05:05, Adrian Glaubitz wrote: Hello, I have a Lifetec LT-7079VTS television (German no-name brand), which is actually a Schneider TV 9.6 chassis. The problem with the set is that it can be turned on but no raster comes up. I have no record of the schneider 9.6 chassis. are you sure it is schneider not beko or something? how old is the set? post some jpegs on fileden.com or you send it and we can try and give more specific help. fault: likely open resistor or bad cap in the RGB stage. star on CRT neck pcb and trace it back from there. -b No Screen supply to the CRT Drive Board, Check the source for open resistor, shorted diode, leaky electrolytic, Etc. Derived off the LOPT. |
#5
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Need help on diagnosing TV with bad HO-Stage
Hello,
b wrote: I have no record of the schneider 9.6 chassis. are you sure it is schneider not beko or something? how old is the set? post some jpegs on fileden.com or you send it and we can try and give more specific help. fault: likely open resistor or bad cap in the RGB stage. star on CRT neck pcb and trace it back from there. -b It's definetely a Schneider 9.6 chassis, it's clearly printed on the PCB .. I am busy today, but I will do further measurements on the CRT-neck-board tonight. Thanks for all your help so far ! Adrian |
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