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Looking for datasheets...

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blight

New Member
Hi!

I am looking for datasheets of the following parts:
STK0039 (hybrid amplifier IC)
2SB915 (transistor)
2SA1491 (transistor)
2SC3855 (transistor)

I guess the 2SC3855 is a matching NPN for the 2SA1491 which is PNP ;)

Thanks!
 

blight

New Member
hmm....
the first link gives me 404 (not found)
the second one gives "unknown host"
and on the third site i do not find information for these parts :(

thanks anyway ;)
 

ChrisP

Member
OK -- here goes...

The STK0039 is available from several sources, but I was unable to locate a datasheet for it. However, it is replaced by the NTE1282 which, though discontinued, is still available as well. Here is what Mouser has to say about it:

Product Comments:
NTE LINEAR INTERGRATED CIRCUIT


526-NTE1282, a Sip-10 Audio Power Amplifier, has been
discontinued by NTE and when stock has been depleted it
will no longer be available.

Currently there is not a cataloged replacement available.
Please contact your Tech Sales representative for
assistance.



5-0800-19
Here is a pinout diagram for the NTE1282, which may help you...



The 2SB915 is functionally equivalent to the BDW84C, so I'm posting a link to that datasheet, as well as those for the 2SA1491 and the 2SC3855...

BDW84C Datasheet

2SA1491 Datasheet

2SC3855 Datasheet
 

blight

New Member
ChrisP: I do not need a replacement for the STK0039 - i have found a shop selling exactly these parts - it's just nice to have the datasheets to check things or try understanding them at least a bit (I am a electronics noob)
the STK0039 is for a damaged technics amp which I have and the other parts are for a damaged yamaha ax-870 which has been at a repair shop (and the guy which has given it to me paid 200 euros for the "repair") and after turning on was only working for like 10 minutes... now i have it :)
I have found a capacitor and 2 resistors which were burnt (the resistors are dark black, not only brown) and there is a little transistor between the big (2sa1491/2sc3855) ones which was also damaged (there was a black spot on the passive cooling-unit where this transistor has touched it and one of the pins seems to have melted so it was no longer connected)... when looking at the other channel I have seen that the damaged transistor (maybe the reason why it blew again after beeing repaired?) is a bigger one than the one of the working channel - this is what I think is a 2SB915 which I am looking for... on the transistor (it's like 4x4x2mm) is (if I read it right) the following code: "BI915" or "B|915" or maybe "B1915" and below is "FT-46"... when looking at the data sheet for the transistor which you said was a replacement for B915 either you are wrong (unlikely I guess) or it is not a 2SB915... any ideas how i could find out which kinda transistor it is and how to find a replacement (if it's a 2SB915 I would know a shop where to buy but without datasheet how shall I know?)

:roll:

Sebi: Thanks for the schmeatic!
 

ChrisP

Member
blight said:
ChrisP: I do not need a replacement for the STK0039 - i have found a shop selling exactly these parts - it's just nice to have the datasheets to check things or try understanding them at least a bit (I am a electronics noob)
Yeah -- I realize that the STK0039 is available -- My posting of the NTE1282 data was as a means of giving you some approximate (or possibly equivalent) information for the STK0039, as the NTE device is supposed to be an exact replacement...

As to the BDW84C vs. 2SB915 -- Note that I said the BDW84C is "functionally equivalent" to the 2SB915. This means that it is a suitable replacement electrically, but may differ physically! Such differences may include but are not limited to case types, pinouts, and/or dimensions.

Again, the info that I posted was for informational purposes -- to help you decide if you had in fact identified the device(s) correctly, or to help you with device pinouts.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Having seen the circuit posted, it's now evident that the STK0039 isn't an amplifier chip, it's just an output stage. In any DC coupled amplifier (like this one) failure of other transistors in the amplifier can commonly blow the output stages. It's good practice, and often essential, to replace all the transistors in the DC chain when you change the output stages.

From your previous posting, you don't appear to have done that, which probably explains why it blew again.
 

blight

New Member
as i am a noob i called the STK0039 amplifiers because they seem to be the last thing which controls the high current for the speakers according to the (already high) input voltage...

can you tell me what is the "DC chain"? is it the part of the circuit where "one half" of the A/C signal is amplified? (like the upper half of the circuit above)

ChrisP: yes, thanks :D from the data sheet your 2SB915 replacement looks 10x bigger than the one i am looking for :shock: ;)


thanks!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
blight said:
can you tell me what is the "DC chain"? is it the part of the circuit where "one half" of the A/C signal is amplified? (like the upper half of the circuit above)
The 'DC chain' is everything which is DC coupled, in this particular amplifier it's everything after the 2.2uF capacitor on the input pin. So you should change all seven of the transistors (assuming your one has seven), any of these faulty (or intermittent) are likely to blow the output chip.
 

blight

New Member
My amp has 10 transistors (for both channels) in the "main" section on the PCB... so I will wait until I get the schematics for this amp (which I have already ordered), then try to make sure the power supply is ok and if it is ok I replace these 10 transistors and it should be ok?
Do ceramic capacitors change their look when they're damaged? Or do they usually not get damaged and not cause transistors to go crazy?

thanks

edit: ok... i checked the damaged STK0039's again (i have 3 now ;))
the one which was damaged when i got the amp has pins 2 and 3 S/C, the two new ones (i also replaced the one which was still ok) now have pins 8 and 9 S/C ... does this mean it could only be a transistor connected to both inputs like the first after "input" in the circuit above? (i have only checked the price for one of the transistor, 2SA798 - dual low noise PNP transistor or something, it's 4 EUR where i have found it so i don't wanna replace all if not neccessary ;)
 

Nigel Goodwin

Super Moderator
Most Helpful Member
blight said:
Do ceramic capacitors change their look when they're damaged? Or do they usually not get damaged and not cause transistors to go crazy?

thanks

edit: ok... i checked the damaged STK0039's again (i have 3 now ;))
the one which was damaged when i got the amp has pins 2 and 3 S/C, the two new ones (i also replaced the one which was still ok) now have pins 8 and 9 S/C ... does this mean it could only be a transistor connected to both inputs like the first after "input" in the circuit above? (i have only checked the price for one of the transistor, 2SA798 - dual low noise PNP transistor or something, it's 4 EUR where i have found it so i don't wanna replace all if not neccessary ;)
Ceramic capcitors are usually very reliable, it's quite rare to find a faulty one.

Looking at the circuit above, pins 2&3 are the bottom output transistor, and pins 8&9 the top one. So, as suspected, the output transistors are S/C. By all means only change the faulty transistors, but make sure you do change them all! - bearing in mind they could be intermittent, and might fail after working for a while. It's like a chain of dominoes - one goes, and they all fall down! - as the output transistors are the devices under most pressure, they are the ones which normally go S/C.

How much do the STK's cost?.
 

blight

New Member
At one shop (which i am not sure about if they have them anymore) it's 7,95 and the other one takes 10,05 EUR - not too expensive but still not cheap ;)

Edit: I have another question :)
One of the metal contacts on the PCB for the STK0039 has mostly gone off the PCB... can I use epoxyd resin to glue it back onto the PCB? or is that liquid silver to repair signal lines good? Or can i get these thin metal pieces with glue on them like stickers?

Edit #2: I have unsoldered every pair of transistors (one from each channel) and checked them in the component tester... all but the last 2 were looking the same. I have made an image showing the difference between the 2 transistors (2SC828 P)... unfortunately either the power supply is somehow damaged or the input stage (treble and bass) is damaged so this will not be the only thing to repair i think :(
The image shows the E->C "flow" of the transistors... does this mean one is damaged or could this be normal?

thanks :D
 

Attachments

mozikluv

New Member
2sc828q

:D hi,

2sc828q is an NPN 250mw 30v 50ma 220Mhz

possible replacements: 2n3704, 2n3707 & 2sc1684

as you have said that 2 pins from the output stage has shorted, check the track foil from the short to whatever parts is connected to that. could be from the input transistor or capacitor. as what nigel has said you have to change all the transistors. this is one weakeness of this kind of set-up, it creates a domino effect. :D
 

blight

New Member
So what now? replace all 10 transistors or try finding damaged ones?
If I replace all 10 and get 2 new STK0039s is there any way to avoid damage of the STK0039s because I don't wanna damage another 2 of them :roll:
Or is it highly likely that replacing all transistors will fix the problem?

mozikluv: I have found all of the 5 types in the "main section" of the PCB (which I guess is the "DC-chain"?) except 2SC1885 in a german shop so i don't need a substitute for the 2SC828 :)

thanks :shock: ;)
 

Nigel Goodwin

Super Moderator
Most Helpful Member
blight said:
So what now? replace all 10 transistors or try finding damaged ones?
I've been doing repairs professionally for over 32 years, we ALWAYS replace all transistors in the DC chain - it prevents the repair bouncing back.

You can easily repair the PCB by simply soldering a piece of wire from the pin of the chip to where it goes.
 

blight

New Member
one more question: is it safe to use different parts (which are listed on some site to be replacements for the original ones) or should one try to find original parts?
I am looking for 2SC1885 transistor :shock: :)

thanks
 

Nigel Goodwin

Super Moderator
Most Helpful Member
blight said:
one more question: is it safe to use different parts (which are listed on some site to be replacements for the original ones) or should one try to find original parts?
I am looking for 2SC1885 transistor :shock: :)

thanks
It should be fine, unless a specific application picks a transistor for a perculiar characteristic they are fairly interchangable.

The 2SC1885 is NPN, 100mA, 750mW, 150V - but as your supply isn't going to be as high as that, the last value won't be critical.
 
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