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Sx750 screwed up

J

Jimhess

New Member
Hi guys, I came here looking for help. I am attempting to recap my sx750 with very little experience. I redid the awk-065 boards and now my phono input does not work and has a loud static noise when I adjust the volume. So I noticed that I accidentally put a 1845 in The q4 location after I had powered it on with a dim bulb tester but had no problems with anything else other than the noise and no phono input. I took the 1845 out of q4 and put in the 992. When I put everything back together and turned it on using the dmb when I adjusted the volume to about half the bulb now lights up and the protection relay clicks . Everything else seems to work normally including the volume on all other settings. I will mention I did completely disconnect the power switch the first time I had the phono boards off because it had previously Ben replaced and the solder was a mess. I checked the voltages at pins 7 and 4 on both boards and they are where they net need to be -19 and 22. Can some one please point me in the right direction?
 
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Make sure the replacement transistor is installed correctly. Check the datasheet for the 992 and then ensure base, emitter, and collector are in the correct positions in the board.
 
As far as I can tell they are. Unless I am looking at it wrong they seem to be pinned the same way as the originals. I will re check my work. Is that the only possibility?
 
Hi, there are probably a lot of possibilities but just a suggestion - a cheap m328 transistor tester is really worth it, in my opinion, just for making sure of the orientation before you install new transistors. I've used mine so much the wires fell off and I had to resolder them. :eek:
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Jimhess said:
As far as I can tell they are. Unless I am looking at it wrong they seem to be pinned the same way as the originals. I will re check my work. Is that the only possibility?
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The 725's and 726's pinouts are opposite of the 992. bce versus ecb.

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ksa992-pinout.jpg
 
Oh my goodness. I don’t know how the heck I looked at that wrong. I am going to flip them and see what happens. Thank you soooooo much. I will let you know what happens!
 
Ok, thanks for the help! Flipped the transistors around and found a bad one in the process. I now have sound on the left channel on phono but not on the right unless I switch to mono. Everything else works as it should. But now when I turn the volume up about halfway the protection clicks on but only on phono. Also I had been having problems with the function of the right channel on other settings previously.
 
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Jimhess said:
Ok, thanks for the help! Flipped the transistors around and found a bad one in the process. I now have sound on the left channel on phono but not on the right unless I switch to mono. Everything else works as it should. But now when I turn the volume up about halfway the protection clicks on but only on phono. Also I had been having problems with the function of the right channel on other settings previously.
Click to expand...
Do you sill have it connected to the DBT when adjusting the volume? If so, it is not uncommon for the DBT to start to glow and affect the relay in this way, depending on the size of the amp and the wattage of the bulb.
 
You
mikiekimi said:
Do you sill have it connected to the DBT when adjusting the volume? If so, it is not uncommon for the DBT to start to glow and affect the relay in this way, depending on the size of the amp and the wattage of the bulb.
Click to expand...
you were correct . That makes sense now lol. I am still having problems with the rh channel though. I am going to lay the schematic out tonight and see what else may be involved beyond the pre amp. Since I had been having issues with it before I started working on it my hunch says it’s further down the line possibly in the power amp
 
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