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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 suggestions on Toshiba TV problem: (Model CF2750K, chassis # TAC-9011, Mf'd Nov 1991) It works pretty well much of the time, but the Automatic Frequency Contol seems to be "straining" to lock on to a channel after changing the channel. It usually takes a second or two for it to "pull in" and lock. Sometimes it does not succeed, and seems to lock in between two adjacent channels....sound from one, and weak video from the other. My intuition is that there may be a single Capacitor-trimmer, or Potentiometer that might "re-center" the "capture-window" and provide more certain "lock-in". Can anyone suggest a specific adjustment, or an approximate location based on a similar model? I do not have a schematic diagram. Thanks in advance! (I was fortunate enough to get excellent advice recently which cured my Vertcal Linearity problems!) |
#2
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I cannot tell you specifics about your set. But, there is a chance that
a component in the AFC detector, or one of its stages that has become off value over time. The preference is to find the defective part, and change it. The AFC detector should be located in the IF amp section. There is a phase detector coil for this operation. If you look on the circuit board, of the IF amp section, you may see something marked AFT to indicate the related area. If you call the parts dealer for Toshiba, you may be able to purchase a service manual, if the model is not too old. At least this little contribution here may be a good start for you. Jerry G. ======== Gene Gardner wrote: Need suggestions on Toshiba TV problem: (Model CF2750K, chassis # TAC-9011, Mf'd Nov 1991) It works pretty well much of the time, but the Automatic Frequency Contol seems to be "straining" to lock on to a channel after changing the channel. It usually takes a second or two for it to "pull in" and lock. Sometimes it does not succeed, and seems to lock in between two adjacent channels....sound from one, and weak video from the other. My intuition is that there may be a single Capacitor-trimmer, or Potentiometer that might "re-center" the "capture-window" and provide more certain "lock-in". Can anyone suggest a specific adjustment, or an approximate location based on a similar model? I do not have a schematic diagram. Thanks in advance! (I was fortunate enough to get excellent advice recently which cured my Vertcal Linearity problems!) |
#3
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I cannot tell you specifics about your set. But, there is a chance that
a component in the AFC detector, or one of its stages that has become off value over time. The preference is to find the defective part, and change it. The AFC detector should be located in the IF amp section. There is a phase detector coil for this operation. If you look on the circuit board, of the IF amp section, you may see something marked AFT to indicate the related area. If you call the parts dealer for Toshiba, you may be able to purchase a service manual, if the model is not too old. At least this little contribution here may be a good start for you. Jerry G. ======== Gene Gardner wrote: Need suggestions on Toshiba TV problem: (Model CF2750K, chassis # TAC-9011, Mf'd Nov 1991) It works pretty well much of the time, but the Automatic Frequency Contol seems to be "straining" to lock on to a channel after changing the channel. It usually takes a second or two for it to "pull in" and lock. Sometimes it does not succeed, and seems to lock in between two adjacent channels....sound from one, and weak video from the other. My intuition is that there may be a single Capacitor-trimmer, or Potentiometer that might "re-center" the "capture-window" and provide more certain "lock-in". Can anyone suggest a specific adjustment, or an approximate location based on a similar model? I do not have a schematic diagram. Thanks in advance! (I was fortunate enough to get excellent advice recently which cured my Vertcal Linearity problems!) |
#4
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![]() "Gene Gardner" wrote in message ... Need suggestions on Toshiba TV problem: (Model CF2750K, chassis # TAC-9011, Mf'd Nov 1991) It works pretty well much of the time, but the Automatic Frequency Contol seems to be "straining" to lock on to a channel after changing the channel. It usually takes a second or two for it to "pull in" and lock. Sometimes it does not succeed, and seems to lock in between two adjacent channels....sound from one, and weak video from the other. My intuition is that there may be a single Capacitor-trimmer, or Potentiometer that might "re-center" the "capture-window" and provide more certain "lock-in". Can anyone suggest a specific adjustment, or an approximate location based on a similar model? I do not have a schematic diagram. Thanks in advance! (I was fortunate enough to get excellent advice recently which cured my Vertcal Linearity problems!) Your guess is probably correct BUT the "Q" of that circuit might be too low for it to work properly. Mold, dust, moisture, breakdown of insulation can cause the Q of a tuned circuit to decrease. The fix would be to PROBABLY replace the coil. I don't think they would be available 13 years after mfg. |
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