Sansui 8080DB Output transistors

[Alex7590]

Hello everyone,

I'm new to this forum so please bare with me if I'm posting in the wrong area. I'm not sure how to do this. Anyway, I have a Sansui 8080DB and I blew up the output transistors, I need to replace them. I do not want to buy those Chinese counterfeits. Does anybody know where I could purchase them, or if there are equivalent transistors that I could install to replace the originals?

Thanks
Alex

 

[Hyperion]

The originals, as shown on the schematic are 2SA747 (PNP) and 2SC1116 (NPN) - these transistors haven't been made for decades and are no longer available.

The only transistors with the same package that you can buy today which get close to those in spec' terms are:-
https://www.mouser.co.uk/ProductDetail/onsemi/MJ21193G?qs=HVbQlW5zcXW72w1fRAP2WA== - for the 2SA747 (PNP)
https://www.mouser.co.uk/ProductDetail/onsemi/MJ21194G?qs=HVbQlW5zcXVQxZkOqmVvOA== - for the 2SC1116 (NPN) - showing out-of-stock

Alternative source
https://www.digikey.co.uk/en/produc...94G/919459?s=N4IgTCBcDaILICkwEZkE4AsBxEBdAvkA
https://www.digikey.co.uk/en/produc...93G/919458?s=N4IgTCBcDaILICkwEZkE4DMBxEBdAvkA

These are a 'drop in' replacement for the originals, however some say that because they have a slightly lower 'Ft' than the originals they are not as good. However for this model of receiver I believe they are fine, and as a bonus they are an order of magnitude more robust.

When output transistors fail they often take other transistors with them depending on how catastrophic the failure was. You need a significant amount of electronics knowledge and skill to diagnose the failure and replace the damaged components, because if you don't find all the failed components 'first time' you can very quickly find yourself with another set of blown Output Transistors, and potentially more collateral damage.

Welcome to AK! and especially the 'Exclusively Sansui' sub forum.

 

[ivandezande]

Hello everyone,

I'm new to this forum so please bare with me if I'm posting in the wrong area. I'm not sure how to do this. Anyway, I have a Sansui 8080DB and I blew up the output transistors, I need to replace them. I do not want to buy those Chinese counterfeits. Does anybody know where I could purchase them, or if there are equivalent transistors that I could install to replace the originals?

Thanks
Alex

MJ21193/4 or 5/6 from Mouser, Digikey, Newark. You'll need new mica or sil-pad insulators as well.

Guessing there's a lot more blown that you need to fix than just the output transistors. Don't break the unit more.

There's many restore threads on the 8080/9090DB and there's much to replace even if the unit is working.

 

[Alex7590]

Thanks for the reply,

The driver board has been referbed also lots of other caps have been replaced. I'm not sure what you mean by mj21193/4. I also need to replace the 2sc1116's. What do you mean by 5/6. Are the mj21193 a direct replacement for the 2sa747's?

Thanks

 

[Alex7590]

Thanks I found them at digikey. I just want to get this correct, The replacements for the 2sc1116 are the 21193G and for the 2sa747's are the MJ21193G?

Alex

 

[DougBrewster]

MJ21193 is the pnp and replaces the 2SA747
MJ21194 is the npn and replaces the 2SC1116
As stated in Hyperion's post above, see the links..

The 5/6 reference in Ivandezande's post is to MJ21195 and MJ21196 which are beefier versions but still useable for this service.

 

[kevzep]

I'd be using MJ15015G and MJ15016G, closer FT to the originals......originals are 15mhz....
Lower FT will work with no problem, but it does affect the sound signature of the amp, some people can tell some can't.

 

[Alex7590]

Thanks kevep, I also ordered those transistors and a rebuild kit for the driver board and recapped the power supply and see how it goes.

Alex

 

[Alex7590]

MJ21193/4 or 5/6 from Mouser, Digikey, Newark. You'll need new mica or sil-pad insulators as well.

Guessing there's a lot more blown that you need to fix than just the output transistors. Don't break the unit more.

There's many restore threads on the 8080/9090DB and there's much to replace even if the unit is working.

How do I find these threads?

 

[kwayde]

In the upper right corner of the Exclusively Sansui page there's a search area. Type in what you're looking for, like 8080DB, and search.

 

[ivandezande]

How do I find these threads?

Google 8080DB restore or 9090DB restore. Pretty simple.

 

[Alex7590]

Google 8080DB restore or 9090DB restore. Pretty simple.

What do I need to do to check the power supply? I have checked the voltages according to the service manual. Is there something that I maybe missing?

Alex

 

[ivandezande]

What do I need to do to check the power supply? I have checked the voltages according to the service manual. Is there something that I maybe missing?

Alex

Did you replace all fusable resistors?

 

[Alex7590]

Yes, I replaced them all, but for some reason even without the output transistors installed, I just turn the unit on and R41 and 42 keep burning up.3 times now that I replaced them. I checked all the transistors on the board and they check out good, also all the diodes are good. I don't know what to do anymore.

Alex

 

[Hipocrates]

I don't know what to do anymore.

Post an extremely detailed explanation of what did you do, along with pictures and whatever measures you did on your power supply and maybe I can help you.
Meanwhile check the big white resistors and check TR11 to 14.
You need to be very precise in order to get help, we are not looking, measuring and do not know anything about your unit and hardly anybody here is a kind of miracle troubleshooter to know what's going with your unit.
And build a dim bulb tester to avoid problems.

 

[Alex7590]

OK, I will post pictures and get more into detail about what I have replaced. Just found out last night that VR03 on the driver board was open, no resistance btw the outside terminals, and the wiper terminal was fixed at 50ohms. I have the newer version board with the 100ohm pots. I hope that this is why R41 and43 were burning up every time I turned the stereo on. Just a quick FYI on the power supply board I check all the resistors .333ohm and all the resistors and transistors on the driver board and power supply board are good. All checked with my Peak DCA75 transistor checker and they are GOOD.. Not one transistor on the driver board is bad, just yesterday I found the open on VR03. I just not sure by looking at the schematic if that variable resistor is open, if it would cause R41, 43 to burn up when you turn the radio on. Just last week I ordered the rebuild kit for the driver board and it will be here today.
Alex

 

[Alex7590]

Just an FYI I triple checked TR11 through 14 and removed them and checked them and they are good. I will be replacing the main filter caps when I can solve the problem first. I really appreciate everyone's help on this matter. I mostly do ham radio repair and just got started doing stereo's so please bare with me.

Thanks
Alex

 

[Alex7590]

I forgot mention that on the schematic for VR03 and VR04 it says that they are 1K ohm, but the actual pots are 100ohm, whats up with that?

 

[Overundr1]

100 ohm is correct.

 

[Hipocrates]

Nice, thank you for the information... Now we can start to see what's going on, you work on ham... you can teach us some stuff around here.
Some comments.

./ Stop with the kits and lets get familiar with the unit, make your own list and buy from mouser or digi key (better components and you going to be sure what's in it) specially if you want to start to do some repair. not to mention less expensive.
./ Replacing caps usually do not fix anything, yes they can cause problems, while adviced on this receivers, is not mandatory they are usually ok.
./ Remember that while the peak devices and such are great tools, but they don tell the whole story, I've seen transistors causing havoc when are installed under use, but that measure ok under the little device and their puny current.
./ Something pulling a lot of current on that little resistor, I'll look in into schematic later. (

I forgot mention that on the schematic for VR03 and VR04 it says that they are 1K ohm, but the actual pots are 100ohm, whats up with that?

Different versions, if you pay attention to the schematic you will find a Vbe multiplier circuit for BIAS (I like that version a lot) , while the version of your board are using use an STVH3 sanken stabistor (basically 3 diodes in series), those things are a pain in the neck to get, so be careful with it.
So Vbe Multiplier circuit.... 1K pot
STVH3 stabistor....100ohm.

Start measuring the power supply just to see if is working fine and post the voltages
Look for broken traces and pads those boards are very delicate and can be broken.