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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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Sony KV-2771R, low sound, good picture
This 1986, 27" set (chassis SCC-552U-A) has excellent video but very low
audio when in TV mode (using the RF input). I suspect the IC in the IF Block, but would appreciate confirmation and information about the IC. With the volume at maximum, the program audio can be heard on the bench, but is still far below what is needed in a normal viewing situation. When using the Video input mode (e.g. signal from a VCR), the sound levels are normal. I have the Sams Photofact (2514). The symptoms along with several other tests the guide describes suggest a fault in the IF Block, IFB-450M. The DC voltages at the IF block connection to the pcb are close to the schematic levels except at pin 6 and pin 10. Pin 6 should be 4.3 V but is 2.8 volt and somewhat unsteady (varies several tenths of a volt) and pin 10, the MPX out, should be 3.5 V but is 0.7 V. Both pins go directly to the IC inside, a Sony 20014X. I've checked the solder joints in the IF block, especially at the coils and at the pcb to case grounds, and have touched up any that looked doubtful. I've also pulled the tuner and checked it for bad joints, to no avail. (This set does not have the problematic stereo board with the bad SM caps so that is not a factor.) The IF Block , p/n 1-464-598-11, is quite expensive. However, I found a cross-reference for the IC itself, labelling it as a CX20014A, which, if this is the correct part, is available at much more reasonable cost (p/n 8-752-050-08). But I have not been able to find a data sheet for the CX20014A that would confirm it is the same as the 20014A in this set. Google did not come up with anything on this model/chassis. Has anyone had experience with audio problems caused by a failed IF block IC? If so, have you replaced the IC and can you confirm that the part number above for the IC applies to the IC in the IF Block of this KV-2771R. Michael Caplan C.E.T. |
#2
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Sony KV-2771R, low sound, good picture
We have never had a single one of those ic's bad.
Lots of bad coils however. Did you try checking the IF and adjustments by inserting a known good IF signal into the set? David Michael Caplan wrote in message ... This 1986, 27" set (chassis SCC-552U-A) has excellent video but very low audio when in TV mode (using the RF input). I suspect the IC in the IF Block, but would appreciate confirmation and information about the IC. With the volume at maximum, the program audio can be heard on the bench, but is still far below what is needed in a normal viewing situation. When using the Video input mode (e.g. signal from a VCR), the sound levels are normal. I have the Sams Photofact (2514). The symptoms along with several other tests the guide describes suggest a fault in the IF Block, IFB-450M. The DC voltages at the IF block connection to the pcb are close to the schematic levels except at pin 6 and pin 10. Pin 6 should be 4.3 V but is 2.8 volt and somewhat unsteady (varies several tenths of a volt) and pin 10, the MPX out, should be 3.5 V but is 0.7 V. Both pins go directly to the IC inside, a Sony 20014X. I've checked the solder joints in the IF block, especially at the coils and at the pcb to case grounds, and have touched up any that looked doubtful. I've also pulled the tuner and checked it for bad joints, to no avail. (This set does not have the problematic stereo board with the bad SM caps so that is not a factor.) The IF Block , p/n 1-464-598-11, is quite expensive. However, I found a cross-reference for the IC itself, labelling it as a CX20014A, which, if this is the correct part, is available at much more reasonable cost (p/n 8-752-050-08). But I have not been able to find a data sheet for the CX20014A that would confirm it is the same as the 20014A in this set. Google did not come up with anything on this model/chassis. Has anyone had experience with audio problems caused by a failed IF block IC? If so, have you replaced the IC and can you confirm that the part number above for the IC applies to the IC in the IF Block of this KV-2771R. Michael Caplan C.E.T. |
#3
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Sony KV-2771R, low sound, good picture
I did check the three coils for continuity and reactance (presence of, not
value). Unfortunately I'm not equipped for IF inject. What were the problems with the coils themselves? Would a defective coil result in the low voltage at pin 10? I though the low voltage at pin 10 of the IF Block would be indicative of an internal failure of the IC, but I guess it could also be a switched voltage depending on the presence of MPX. According to the Sams, if when injecting an audio signal at pin 10 of the Block one sees (scope) the audio at pin 9, the Block is defective. That is the case here, but I appreciate that does not mean that it has to be the IC itself. Wish I had a data sheet for the IC. Michael "David" wrote in message ... We have never had a single one of those ic's bad. Lots of bad coils however. Did you try checking the IF and adjustments by inserting a known good IF signal into the set? David Michael Caplan wrote in message ... This 1986, 27" set (chassis SCC-552U-A) has excellent video but very low audio when in TV mode (using the RF input). I suspect the IC in the IF Block, but would appreciate confirmation and information about the IC. .. . . I have the Sams Photofact (2514). The symptoms along with several other tests the guide describes suggest a fault in the IF Block, IFB-450M. The DC voltages at the IF block connection to the pcb are close to the schematic levels except at pin 6 and pin 10. Pin 6 should be 4.3 V but is 2.8 volt and somewhat unsteady (varies several tenths of a volt) and pin 10, the MPX out, should be 3.5 V but is 0.7 V. Both pins go directly to the IC inside, a Sony 20014X. .. . . . Has anyone had experience with audio problems caused by a failed IF block IC? If so, have you replaced the IC and can you confirm that the part number above for the IC applies to the IC in the IF Block of this KV-2771R. Michael Caplan C.E.T. |
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