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SX-550 with factory transistor installed incorrectly??? AF Muting Board

triplegee77

triplegee77

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Are my eyes/brain completely shot, or is this factory transistor installed incorrectly??? I have no sound output but all test points measure correctly (and I triple-checked all of my work). This is Q3 on the AWM-101 AF Muting assy. When I measure voltage on what should be the collector (per the silk screen and schematic), instead of 8.4V I'm getting close to 16v on all three(C, B, E) and -4v on the collector of Q4, which should be -19V. On the AWM-101 I replaced three caps and Q4 during my recap and I seem to remember that Q4 appeared to be installed incorrectly, but I installed the new one according to the schematic and the board silk screen. I guess I'll try turning Q3 to the correct orientation, but my question is, could this unit be functioning with both Q3 and Q4 installed incorrectly?

IMG_0371.JPG
 
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I think the 2SC945 transistor matches the silkscreen: ECB
Now that being said, is this an original 2SC945 or a KSC945? If it's a KSC945, it's wrong because only a KSC945C has the same pin out as the 2SC945.
Look at the datsheet for KSC945.

This is why MTF will not recommend this part number for a replacement.
 
redk9258 said:
I think the 2SC945 transistor matches the silkscreen: ECB
Now that being said, is this an original 2SC945 or a KSC945? If it's a KSC945, it's wrong because only a KSC945C has the same pin out as the 2SC945.
Look at the datsheet for KSC945.

This is why MTF will not recommend this part number for a replacement.
Click to expand...
OK, Thanks! It is what was in it when I bought it so I'm guessing original. Guess I was looking at what I remember as CBE (been 30+ years so I'm rusty). So what do you think would cause all off the voltages to be off so much - B C and E? all the PIN voltages seem to be correct - 9 through 6 when measured to gnd pin 10. I got very close to these voltages:


IMG_0361_1.jpg
 
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I would not assume this is a factory transistor. I would check the pin out with a DMM set to diode mode. It will tell if the junctions are good and the direction you expect.
 
Thanks. Looks like the transistor is correctly oriented. I must have been looking at the wrong pinout somehow. When I looked it up again, it is ECB as you said.
 
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