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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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Problem with KV27XBR35
Have no schematics, nor service manual, trying to rescue this huge work of
art tv from the dump... symptoms: picture goes off and on repeatadly once per second, colors are way off, sound OK. Scoped the RGB signals going to the CRT board and indeed they all go on and off as the picture does. Checked for poor solders on the main board and the power supply board, only found one transistor with weak joints, but the problem persists. I didn't manage to make the problem go away or get worse by banging all over the place, so it does not seem to be an intermittant connection, maybe a permanent disconnect? Going out of the PS board, one of the supplies (orange wire in the 5 wire cable) is marked as 24V on the board, but it is actually 20V, yet it is stable on the scope. When disconnected the connector going to the main board (removed the load) the voltage rises to 24V, so possibly somthing oveloads it. Your help is much appreciated. |
#2
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In some models of the Sony sets, the AKG bias drive will cycle the CRT
brightness off and on, when the CRT is very weak. If this is the case, you may be able to frig it a bit, by increasing the screen bias to have more beam current. Increasing the screen bias will also accelerate the wear of the cathodes, but it is an old tube anyways. When you raise the screen bias, you may find that there will be retrace lines, but the brightness cycling should stop. The fix is to change the CRT. -- Jerry G. ====== "DavidA" wrote in message lkaboutelectronicequipment.com... Have no schematics, nor service manual, trying to rescue this huge work of art tv from the dump... symptoms: picture goes off and on repeatadly once per second, colors are way off, sound OK. Scoped the RGB signals going to the CRT board and indeed they all go on and off as the picture does. Checked for poor solders on the main board and the power supply board, only found one transistor with weak joints, but the problem persists. I didn't manage to make the problem go away or get worse by banging all over the place, so it does not seem to be an intermittant connection, maybe a permanent disconnect? Going out of the PS board, one of the supplies (orange wire in the 5 wire cable) is marked as 24V on the board, but it is actually 20V, yet it is stable on the scope. When disconnected the connector going to the main board (removed the load) the voltage rises to 24V, so possibly somthing oveloads it. Your help is much appreciated. |
#3
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When you say colors are way off, what do you mean?
The odds are very high the picture tube is simply at the end of its life and the AKB circuit is blanking the video. A google groups search will go a long way in your quest for information. David |
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