Pioneer SA-1000 hi filter

[The Fuxtor]

I refurbished one of these units a while back , but have discovered one small issue. The high filter switch seems to be operating in the wrong settings? At no filter setting, it would seem to be at the most filtered, at the filtered setting it is turned off if this makes sense? There are 3 filter settings for high... 6 kHz , 12khz and off. I am guessing that seeing the only components changed on this filter board were caps and transistors , is perhaps I installed the high filter transistors backwards?? Would this make sense??? I will attach a snip of the filter scat to check. The high filters tie into points 11,12,13,14.....

 

[rcs16]

Who knows what you did, but you can verify that the bjt is installed correctly, whatever you used as a replacement.
Measure the transistor terminal voltages, it is a common emitter npn ckt, base is +0.6V above emitter, collector is at the supply V,
you can calculate the emitter current, Ve / 3900, it should be in the mA range.

 

[The Fuxtor]

Who knows what you did, but you can verify that the bjt is installed correctly, whatever you used as a replacement.
Measure the transistor terminal voltages, it is a common emitter npn ckt, base is +0.6V above emitter, collector is at the supply V,
you can calculate the emitter current, Ve / 3900, it should be in the mA range.

Thanks for the reply, before I dive back in ,, would a incorrectly installed bjt exhibit these " backward " symptoms??
I got the vetted tranny and cap list from a thresd here on AK.

 

[rcs16]

I am not sure what is causing your issues but it is possible if it worked fine before changing out the 2sa870, and you changed them, now it has a problem, first place to verify device pinouts, bias etc.

 

[The Fuxtor]

I am not sure what is causing your issues but it is possible if it worked fine before changing out the 2sa870, and you changed them, now it has a problem, first place to verify device pinouts, bias etc.

Yes, maybe I'm just stalling! Lol... A bit of work to check . Not sure if this was how it was originally but who knows....
Seems to only make sense ? If a cap was backwards it wouldn't be happy!

 

[llwhtt]

Those transistors are being used as emitter followers, if installed incorrectly you get nothing on the output. The transistors will only pass along, base to emitter, whatever signal is applied to the base. The transistors themselves are not filters only the components preceding them are the filter components, resistors and capacitors.

Craig

 

[The Fuxtor]

Those transistors are being used as emitter followers, if installed incorrectly you get nothing on the output. The transistors will only pass along, base to emitter, whatever signal is applied to the base. The transistors themselves are not filters only the components preceding them are the filter components, resistors and capacitors.

Craig

Ok, I wasn't sure... I was looking at it thinking if the transistor opens up and passes signal to the filtering components or it stays off and forces the signal thru the other path which would be a bypass? So if this is not the case, what would make sense looking at that snip of scat??

 

[llwhtt]

The signal is travelling left to right on the schematic. The main inputs to the filter board are pins 3 and 4, the outputs are 9 and 10. All of the components before the bases of the two transistors comprise the filter network including the off board switches, the rectangular boxes of dashed lines. The transistor is biased as Class A, the only class that would work since there is only one transistor per channel. So the transistor is always on and it's conductance controlled by the signal.

Craig

 

[The Fuxtor]

The signal is travelling left to right on the schematic. The main inputs to the filter board are pins 3 and 4, the outputs are 9 and 10. All of the components before the bases of the two transistors comprise the filter network including the off board switches, the rectangular boxes of dashed lines. The transistor is biased as Class A, the only class that would work since there is only one transistor per channel. So the transistor is always on and it's conductance controlled by the signal.

Craig

Ok, well from what you are saying I almost have to think this was like this before I got my hands into it.. looking at the schematic again shows I would have only replaced 6 components , 4 small caps and the 2 transistors, all of which wouldn't work if installed incorrectly. I was also looking at the unit thinking maybe somehow I returned the switch back to the chassis " upside down " but that is not the case as the center position is the off position.
I can't remember now if had to remove the wiring from this board, but thinking I should be able to just reverse some of the wiring to the switch and that would work?

 

[llwhtt]

An o'scope and signal generator would let you know for sure.

Craig

 

[The Fuxtor]

Update! Got some time and opened er back up to see what was up... I had one of the 2 transistors installed wrong! Pulled it and replaced it and much, much more improvement now. Filters work as they should but also less distortion in the bass? Much nicer sounding.