Stumped: SX-990 Transistor Replacement

[Stillhouse]

Ordered all the caps and transistors (aside from KSC1845, backordered) to renew my SX-990 and they arrived yesterday. Followed the lists from this thread:

http://www.audiokarma.org/forums/in...er-sx-990-receiver-problems-questions.485154/

I'm off to a good start with the caps, but the transistors are causing me to scratch my head. For starters, Q7 & Q8 on the main amp board(W15-060) appear to be PNP according to the service manual and board while the replacements(KSC2383) are NPN. So my question is how does one make such a replacement when those types work differently? Specifically, how would I orient the emitter, base and collector?

 

[moodydan]

Q7 and Q8 should be 2SC497’s, correct? So there shouldn’t be a problem. There are also 2SA497’s on that board from the looks of the list you posted which may be causing confusion. Did you visually check for 2SC497 at Q3, Q4, Q7, and Q8?

 

[Stillhouse]

Actually, Q7 & 8 are 2SA497. 3,4,5,6 are 2SC497.

Drat it!! Just re-re-rechecked everything and turns out:

1. The lists in that thread don't match what is in my unit. Or are wrong.

2. I didn't order enough transistors, came up two short on the 2SC497 replacements.

 

[larryderouin]

Don't knock yerself out. We've all BTDT @ one time or another. Some have the T-Shirt, some have the book, and more than a few have watched the movie. (NOTE TO SELF! The book is better!). PIONEER did some crazy stuff back then, but no worse than most and a hell of a lot less than Sansui.

 

[zebulon1]

Don't knock yerself out. We've all BTDT @ one time or another. Some have the T-Shirt, some have the book, and more than a few have watched the movie. (NOTE TO SELF! The book is better!). PIONEER did some crazy stuff back then, but no worse than most and a hell of a lot less than Sansui.

Copy that!
A guy is bringing a 22000 over for me to look at. Looking forward to messing with it but the Sansui repair/scat can be difficult.

Back to the thread!

 

[Stillhouse]

I skipped changing out the transistors(aside from mains) and got the board back in after finishing up with the caps, aside from the big output can capacitors which I will eventually replace. So far so good, up and running and sounding better than before.

 

[larryderouin]

Great News. Don't Rush. One board at a time.

 

[Stillhouse]

Indeed. Trying to decide what to do next. Got parts for the head amp(W15-049), control amp(W15-079) and power supply(W16-022). Voltages on power supply read:

B1(56v) = 60v
B2(40v) = 37.3v
B3(25v) = 26.6v
B4(18v) = 18.8v
B5(12v) = 12.3v

Not far off what they should be.

 

[john stumpf]

power supply first

 

[Stillhouse]

Update:


After getting the KSC1845s I ordered back in December I jumped back into working on my SX-990. Power supply got recapped and a refresh of transistors. Then I finished the work on the main amp board. Had already replaced the main output transistors and capacitors back in December, and waited to complete the job until I had the rest of the parts on hand.

All I can say I am bowled over by what a difference this has made. This receiver went from good sounding to great! Firstly it is as if a curtain has been drawn back from the soundstage and more detail comes through. Instruments have better positioning and separation. Bass was much improved, with greater punch and depth without being flabby or overpowering.

I still have the head and control amp boards to do and look forward to getting to that, but for a while now I'm just going to enjoy some music through this baby!

Many thanks to all users who have help in this thread and others!

 

[zebulon1]

Underrated receivers, wonderful sound!!