SpiffMcSpiff
New Member
Alright so here goes. I'm working through some self inflicted issues with a Sears LXI 564.92581 receiver and finally decided I should swallow my ego and see what kind of responses I can get out of the AK community. I'm lacking in knowledge in stereo repair but am comfortable with multi-meter usage and have a lot of familiarity with residential electrical work. My day job is an IT network administrator so I'm used to digging to the ends of the earth for a end game solution. I also have an analog oscilloscope but I haven't been comfortable to start using it.
So onto the meat. I have a Sears LXI 564.92581 receiver that appears to be stuck in protect mode. Receiver turns on but the relay will not click and the display doesn't light up. Here is what I know so far.
1.This started after mistakenly crossing the leads on transistor Q351 (see image files below). My own fault on this one and I've learned my lesson.
2. I've tested and ruled out an AC Detector issue, DC offset detector issue, and overload protection issue on page 22 of the service manual that I was able to find.
3. Q351 burned out and was replaced. I'm trying to follow along pages 51 and 52 and I'm confused at the value of what appears to be 35.2 volts at the base. This doesn't make sense to me as a calculator shows that 54v running through a 1000r and then a 390r should be somewhere around .001 which is what I'm getting when testing.
4. I'm getting correct voltage values on the collector of Q351 and Q352 (+/- 1-2 volts) although it appears that the base of Q352 relies on voltage form Q351 so I guess that needs to be right first.
5. Service manual located here. Model number is slightly different but internals such as power-amp, tuner, etc appear to be identical. https://www.hifiengine.com/manual_library/sears-lxi/564.shtml
I'm open to any suggestions that get me on the right path. Even if it means that I table this project to step back and invest in learning. This is a cheaper end stereo and I've been attempting to use it as a learning tool so I'm not worried about spending a few bucks as long as it provides a learning opportunity. My end game is to develop some familiarity with these types of products so I can keep them running down the road.
So onto the meat. I have a Sears LXI 564.92581 receiver that appears to be stuck in protect mode. Receiver turns on but the relay will not click and the display doesn't light up. Here is what I know so far.
1.This started after mistakenly crossing the leads on transistor Q351 (see image files below). My own fault on this one and I've learned my lesson.
2. I've tested and ruled out an AC Detector issue, DC offset detector issue, and overload protection issue on page 22 of the service manual that I was able to find.
3. Q351 burned out and was replaced. I'm trying to follow along pages 51 and 52 and I'm confused at the value of what appears to be 35.2 volts at the base. This doesn't make sense to me as a calculator shows that 54v running through a 1000r and then a 390r should be somewhere around .001 which is what I'm getting when testing.
4. I'm getting correct voltage values on the collector of Q351 and Q352 (+/- 1-2 volts) although it appears that the base of Q352 relies on voltage form Q351 so I guess that needs to be right first.
5. Service manual located here. Model number is slightly different but internals such as power-amp, tuner, etc appear to be identical. https://www.hifiengine.com/manual_library/sears-lxi/564.shtml
I'm open to any suggestions that get me on the right path. Even if it means that I table this project to step back and invest in learning. This is a cheaper end stereo and I've been attempting to use it as a learning tool so I'm not worried about spending a few bucks as long as it provides a learning opportunity. My end game is to develop some familiarity with these types of products so I can keep them running down the road.
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