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