Technics SU-8080 driver transistors

[rokoc007]

Hello guys,

I would like to ask you about 2sc1913/2sa913. My amp has issue on the left channel, driver transistor 2sc1913 has open B-E junction. It is still playing but with distortion on that channel due to zero bias voltage.. So I have to change them, I don't want to buy some 2sa1913 ebay fakes..

I did some research here and found some possible replacement :

2SC3298/2SA1306
2SC5171/2SA1930
2SC2238/2SA968
2SC4793/2SA1837

SU-8080 has 2SD427/2SB557 high power output transistors. I decided that I will use 2SC5171/2SA1930, they are faster (200mhz) but then I check SOA and I am not sure..

Do you have some experience with similar problem ?

Thanks a lot

Robert

 

[JoseHH]

Hi and welcome to Audiokarma!!
If the orignal drivers were the 2SA913A/2SC1913A, then the 2Sa1930/2SC5171 are better because of their higher voltage tating. If you had the 2SA913/2SC1913 then you could use the 2SA1837/2SC4793. Another alternative is the 2SA1011/2SC2344
Replace both channels to make sure you get a left-right balanced performmance.

 

[rokoc007]

thanks a lot JoseHH, so I will use 2sa1837/2sc4793. Not sure if they will be original, I mean from our local shop, but I hope that it will be good.

 

[JoseHH]

Hello,
The ones i linked are genuine. Were are you located?. You can post photos of what you can get so we can tell if they are genuine parts or not.

 

[rokoc007]

Europe, shipping cost more than transistors.. Sure, I will make photos when they arrive.

 

[JoseHH]

If you are in Europe, then this may be more competitive:
https://www.profusionplc.com/parts/2sc4793lb-tf3t
https://www.profusionplc.com/parts/2sa1837l-tf3t
These parts are made by Unisonic, which is a Taiwanese company. They make reliable parts.

 

[rokoc007]

okay, thanks for the tips. I post the photos of transistors when they arrive. If they will be suspicious I will order them from profusionplc.com. Also found leaked caps, two of them, so maybe is good time for recap it.

 

[JoseHH]

OK. Please consider starting the recaping step only after you have replaced the transistors and once the amplifier is working again. Otherwise you may run into additional issues. Once you fixed the issue, then you can recap board by board. Also have a dim bulb tester at hand. You will need it to power-up the unit after you have replaced the transistors. It will prevent major damage in case that something else is shorted.
Check the emitter resistors (between the emitters of the power output transistors) and also check all the resistors that are directly connected to the transistors that tested bad. Some resistors may have gone open when these transistros failed. Do you have a service manual?. If not, try to get one from HiFi engine. It is free.

 

[rokoc007]

yes I have manual. That's my plan. Do it in one step, not so good idea

 

[rokoc007]

driver transistors arrived today, so I make some pictures. It is from verified supplier, so I hope that's not be a fakes..

 

[JoseHH]

The 2SA1837 looks genuine.
The 2SC4793 is suspicious. It may be a knock-off. For comparison, later today I can PM you a photo of the ones I have which I know are genuine.
In the picture I can not see if the numbers are split like the "8" in the 2SA1837. Look at the 9, and compare it carefully with the font of the 2SA1837. Also compare the number 7 among the parts.

 

[rokoc007]

the font is the same I think. It is quite hard to make detailed photo

 

[JoseHH]

Iooking at the pictures that you posted carefully and comparing with the parts I have I believe that both the 2SA1837 as well as the 2SC4793 that you bought are genuine. I sent you a PM with the pictures of the ones I have which I know that are made by toshiba.
Did you check the output transistors?.

 

[rokoc007]

Hi Jose, thank you for confirmation, yes I checked them, all good. Actually, I put them there and everything works well. Now I am able to set bias voltage to 15mV. I did also some testing, at first I changed transistors on that broken channel, then listen music to compare if there is some differences between channels, but I didn't hear any, so I think that these transistors were good choice.

 

[JoseHH]

Excellent news!. I am glad you could fix your amplifier.

 

[rokoc007]

Hello guys, yes, me too I did recap with measurement of all capacitors. They were not bad at all, but I found some bad on the phono stage. Also 1000uF on the amp board were not in ideal condition. Also cleaned that flap switches and output relay Now they work as it should works But it isn't so easy to take them out and clean..

 

[EC1]

wow, nice job, got one here sitting. maybe I should pull it out again and do the same.