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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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On Friday, August 30, 2002 at 1:22:07 PM UTC+2, Shaun Davy wrote:
Am doing repairs on a Pioneer Stereo XR-P740M with amp problems. Its that one with the 2 halves mounted around the fan!!Problem started when there was trouble with the tape deck (owner induced) 2 buttons were pressed at once. after that a tape belt started slipping when unit initialises or other deck is used. in investigation of that (by owner) it started blowing fuses. Now the output transistors are blown. Tape deck has now been unplugged from main pcb. Replaced transistors and again blown. Have looked at Amp section and looked for info on this amp and found that a bad 220 ohm resistor can cause this fault, checked board and one of the 2 power transistors (2SA1264) has a bad resistor that looks blown and can't read print on it (R7547) it is across B-E junction like the other power transistor. My plan of attack is to replace transistors 2SA1264 & 2SC3181, the smd resistor and put in a 1A fuse to start with to make sure im not going to blow transistors. Also seen info where a bad tape motor can cause these transistors to blow. Can i try the above with the tape deck still unplugged? and if so can i plug the tape deck back in and not be worried about blowing op transistors again. I know this amp is a beast but would really like to get it running again. Any suggestions appreciated Shaun Hi Shaun Did you manage to get the fault on the power amp? I two have an xr-p740m that keeps blowing fuses. If I switch the unit on without the power amp connected it doesn't blow the fuse , but as the power amp module also include the voltage regulators it might be something further down the power rail. Perhaps a bad cassette motors like Lindsey and/or Aaron mentioned. I have desoldered all the trough hole transistors and did not find any short on any off them. My R7547 test 220ohm without me desoldering it. This looks like a really awesome amp and would love to get it running again. If you have any info to spare on the problem or unit I would really appreciate it. Do you know if this unit would function normally if the tape and CD units are disconnected? Sorry for my bad English :-( Regards Bennie van Eeden |
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