Pioneer SX-990_Transistor Mystery

[David Weaver]

I recently acquired a Pioneer SX-990 that after a little cleanup/deoxit sounds pretty darn good!
Cosmetically it is in great shape and sounds very good but there is some noise with no signal and the volume turned up.
I had recapped the power supply and pre-amp and although the tone came alive, she still had some background noise.
I figured I would recap and replace the transistors on the amp board as well to freshen her up and in the process, potentially solve the hum issue.
I planned to use KSA1013's and KSC2383's to replace the 2SA497's and 2SC497's respectively, as per the schematic/parts list.



Once I removed the board, I realized only the PNP was correct. The NPN's were 2SC485 and 2SC627 and from what I researched the 627 is somewhat unique.
The question I have is: Is this common on Pioneer gear and more importantly, would I be ok if I replaced the parts in question with the 1013/2383's as per my original intentions?
I'd appreciate any input that would help me with this mystery!

 

[markthefixer]

rehashing old info:
Q1 2sc732 > ksc1845 position needs gain
Q3 2sc497 > ksc1845 position needs gain
Q5 2sc497 > ksc2383 position needs current drive
Q7 2sa497 > ksa1013 position needs current drive
Q9, Q11 2sc793 > MJ21194G

Please detail what position (Qx) has which transistor number.

useful information:
2sc485 si npn to-39 80v 1.5a 0.8w ft 10mhz 30hfe
2sc627 si npn to-39 200v 0.1a 0.7w ft 10mhz 360hfe

 

[David Weaver]

rehashing old info:
Q1 2sc732 > ksc1845 position needs gain
Q3 2sc497 > ksc1845 position needs gain
Q5 2sc497 > ksc2383 position needs current drive
Q7 2sa497 > ksa1013 position needs current drive
Q9, Q11 2sc793 > MJ21194G

Please detail what position (Qx) has which transistor number.

useful information:
2sc485 si npn to-39 80v 1.5a 0.8w ft 10mhz 30hfe
2sc627 si npn to-39 200v 0.1a 0.7w ft 10mhz 360hfe

Thanks for re-hashing this info for me markthefixer.
I researched the forums prior to posting but I could not find reference to the use of 2SC627.
Regardless, here are the transistor positions:

Q1 - 2SC732. - will replace with similar hfe KSC1845
Q3 - 2SC627 - schematic indicates 2SC497
Q5 - 2SC485 - schematic indicates 2SC497
Q7 - 2SA497 - board matches schematic.
Q9, Q11 are original 2SC793's - will retain in this unit. (Note: the mains run fairly warm (about 95 F) with the bias set at 10mv)

 

[markthefixer]

the parts numbers that you found in it were probably available replacement parts from some work long long ago.

my post 2 recommendations stand as is.

 

[David Weaver]

the parts numbers that you found in it were probably available replacement parts from some work long long ago.

my post 2 recommendations stand as is.

Thanks again!
I have plenty of 1845's in the 450hfe range.

I'll post my final results but here is where I'm at currently:

 

[SinglePoint]

While it's all apart, consider replacing those 0.5ohm 2w resistors (on the output emitters). I had one go open, along with the trimmers...

 

[markthefixer]

let us know if the TO-92L driver transistors get "ouch" hot.

in that case

757-TTA004BQ & 757-TTC004BQ TO-126's with heat sinks would be indicated.

 

[David Weaver]

While it's all apart, consider replacing those 0.5ohm 2w resistors (on the output emitters). I had one go open, along with the trimmers...

Thanks for the advice.
I will get them on my next Mouser order.

 

[David Weaver]

let us know if the TO-92L driver transistors get "ouch" hot.

in that case

757-TTA004BQ & 757-TTC004BQ TO-126's with heat sinks would be indicated.

Looks like Mouser has the T0-126's in stock, however, I have a fair amount of KSA1220AYS/KSC2690AYS on hand. The spec's seem fairly close. What are your thoughts on using them instead? I used them with heatsinks on my Luxman L-480 (see pic) but getting a T0-126's + heatsink may be difficult as this board is fairly cramped for space as it is.

 

[markthefixer]

yes i know it's crowded. that's why i said if.

they might not heat up badly.

don't go looking for trouble, plenty of cans of worms to go around.

 

[David Weaver]

yes i know it's crowded. that's why i said if.

they might not heat up badly.

don't go looking for trouble, plenty of cans of worms to go around.

I'll go with your original recommendation and I'll let you know the results!

 

[David Weaver]

Just thought I'd report back that the 990 is coming along very nicely!
The amp board transistors are are running cool and the mains are running around 92deg F.
The buzz did not go away until I recapped the head amp and replaced the 458's.
I swapped out the MPX unit and I have stereo now but the mute is still not working.
Kinda has me perplexed as I replaced all but the resistors and the trimmer.
I like the aesthetics and the warm sound of this series. So much so, I bought a 1500td and another 990!
Thanks for the help!