Poorly Sansui AU-2900

[RolyShoes]

I am dubious about them actually. Aside from looking up the specs of components, how can I tell which replacements would work from the service manual schematic? Identifying the NPN/PNP transistors is easy but I can't see a comprehensive detailed breakdown of the properties. Makes it difficult to work out what to fork out on.

 

[Oldsansui441]

Hi, https://english.electronica-pt.com or http://alltransistors.com/ are good cross reference sites but always compare data sheets as well. There are plenty of transistor lists and cross references here on AK also, just search 2sa726 or 2sc1313 sub for results. Here is a thread that may be helpful. http://www.audiokarma.org/forums/index.php?threads/once-more-sansui-transistor-substitutions.583009/
Yes the service manual won't show transistor properties, so it just comes down to some studying of above for matching components. All the best with your project .

 

[RolyShoes]

Thanks for that - at least I'm not missing anything I guess. I've ordered the recommended transistors so fingers crossed I'll be a little closer to success by the end of the week. Happy New Year!

 

[Oldsansui441]

Your welcome, yes looks like you have it covered. Thank you, Happy New Year to you also.

 

[ArnoArno]

Hi all,

Sorry for reviving this old thread but it describes exactly the problems I'm having. I have found the main issue: the 5-pin transistors (2SA798) on the main board. I swapped them out for 2 x ksa992fbu in this config:

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This made the make the crackels and pops go away. Additionally I replaced the 2 big capacitators as they were leaky. Also the 2AS726's with ksa992fbu's and the 2SC1313's with KSC1815 as suggested in this post.

However I'm still left with an issue. The sound on my right channel is distorted. It is only distored when I use a speaker, headphones only works fine. If the speaker is active then the sound is also distorted in the headphones. Can anyone give me a hint were / how to look? I can't visually see any issues with the caps etc. Also the new combi-transistor doesn't seem to be the issue as I can interchange them and the issue doesn't switch sides.

 

[Oldsansui441]

Also the 2AS726's with ksa992fbu's and the 2SC1313's with KSC1815 as suggested in this post.

Hi, did you mean replaced 2SC1313's with KSC1845's?

You will need to check your unit for fusible resistors (some 2900's have them and some don't), there may be four standing up off the board just in front of the heatsink. If they are there, they have likely drifted in value. There may also be one on your pre amp (edge of board) and some on power supply.

Have you also checked your DC offset and bias? Yes those KSA992's pairs are good subs for the original dual transistor and won't be causing your problem.