SX-950 phono issues

[Islander21]

Today my SX-950 started making some serious static noise on both phono inputs, whether the TT was connected or not. It sounds fine in AUX and on AM/FM. On stereo mode the left channel is clean with good sound, the right channel is very staticky with no sound. In mono mode the left channel becomes staticky as well but not as bad as the right channel which behaves exactly as in stereo mode. I swapped in my SX-850 in and it works fine, so it's not the speakers, cables, the Kenwood KD-750 turntable or the equalizer. I cleaned all the switches thoroughly DeoxIT, did I screw something up or perhaps did my phono board just take a dump?

 

[mbz]

Don't know the unit

Symptoms read like faulty silicon in right channel phono stage.
Schematic shows 2SA725 and 2SC1313 used. Both of these are considered problematic (shoot on sight?)
If you have the skills then replace, maybe KSA992 and KSC1845?

 

[Islander21]

Thanks for the reply, MBZ. I do have are a very particular set of skills. Skills I acquired over a very short USAF career. Skills that make me a nightmare... er, never mind. Should I consider doing a full phono board recap/repair? The recap kit I'm looking at has at least 4 transistors in the phono stage baggy. I acquired this unit recently and the seller provided a repair invoice from 2024, I see that that the tech replaced 4 signal transistors and two electrolytic caps in the phono EQ circuit (no details, though). Might that be a hint?

 

[mbz]

Would prefer if the Pioneer guys chimed in...

I see that that the tech replaced 4 signal transistors and two electrolytic caps in the phono EQ circuit

A guess (safe bet) is that they replaced the 4 of 2SC1313. Would have preferred that they also replace the 2 of 2SA725, both of these transistors appear on the top 10 list

Thread 'Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements'

Sep 1, 2016

I've followed AK advice for several vintage solid state receivers now and the difference in sound, from recapping and from replacing "known-to-be-noisy" small signal transistors to be amazing.

While following along with others' threads and trying to help out with "consider replacing these known-noisy transistors", I've tried to find a "top ten list" or "worst transistors" thread, but found none.

If there is a long-standing "which transistors go bad or go noisy and you should replace when you can" thread, please post a link.

If not, please contribute your "worst, replace ASAP"...

• dlucy
• Replies: 551
• Forum: Solid State

• 

Should I consider doing a full phono board recap/repair?

Depends if you listen to vinyl much. As a minimum the fault needs to be fixed.
C1,2(1uf/25V) and C11,12(3.3uf/25V) are electrolytics in the audio path, you will get a slight improvement by replacing these with MKS film caps

Suggest post a pix of the phono board so we can see what has been done, identify the transistors C1845?? C1313?? A725?

I wouldn't rush buying a capacitor kit before knowing what the tech has done
Phono board below.

 

[Islander21]

Would prefer if the Pioneer guys chimed in...


A guess (safe bet) is that they replaced the 4 of 2SC1313. Would have preferred that they also replace the 2 of 2SA725, both of these transistors appear on the top 10 list

Thread 'Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements'

Sep 1, 2016

I've followed AK advice for several vintage solid state receivers now and the difference in sound, from recapping and from replacing "known-to-be-noisy" small signal transistors to be amazing.

While following along with others' threads and trying to help out with "consider replacing these known-noisy transistors", I've tried to find a "top ten list" or "worst transistors" thread, but found none.

If there is a long-standing "which transistors go bad or go noisy and you should replace when you can" thread, please post a link.

If not, please contribute your "worst, replace ASAP"...

• dlucy
• Replies: 551
• Forum: Solid State

• 

Depends if you listen to vinyl much. As a minimum the fault needs to be fixed.
C1,2(1uf/25V) and C11,12(3.3uf/25V) are electrolytics in the audio path, you will get a slight improvement by replacing these with MKS film caps

Suggest post a pix of the phono board so we can see what has been done, identify the transistors C1845?? C1313?? A725?

I wouldn't rush buying a capacitor kit before knowing what the tech has done
Phono board below.

I'll take care of that this week-end and post some pics. Thanks!