Which replacement transistor for Sanken C3856/A1492?

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#42
rkc7 said:
Well, I got replacement parts for the one channel, and tested it out and it worked fine... for about 10 min. Lights dimmed and the amp smoked... oops.

The channel I fixed was fine, but the other channel blew some outputs. So, I again bought entirely new outputs transistors for the channel and replaced the drivers as well. Checked it over thoroughly and figured it was just because I had mixed some of the "good" transistors left over from each channel previously to fix the 2nd channel, but they may have been unknowningly damaged.

Then I had another problem which I finally just solved!

After I repaired ch 2, when I tested the amp, the protection light would not come on when I turned it on and the relay would never click on the channel.... so after countless hours of searching components and tracking down the source of the problem, I noticed a small crack on the edge of the volume control board which happened to run through the leads of a couple components, and with the ohmmeter saw that the trace that powered the LEDs for the channel was open. So, I repaired the trace and secured the crack with some epoxy and it worked!

It's been a long an arduous journey to repair this amplifier, so I hope it will finally work correctly! I think I just want to get rid of it now, so I no longer have to be concerned with it.

I've definitely not been impressed with Samson's amplifiers. I also have a servo 120 which had it's fair share of problems. These included a few component's that must have had cold solder joints as the solder cracked right off the board... most annoying being the relay to turn on the speakers which manifested itself as the speakers randomly turning off and having to give the thing a whack to turn them back on 😀

Oh, and if anyone is looking for the 2SC3856 or 2SA1492, I bought some from this company and even smashed one open and they are genuine for a great price!

B&D Enterprises: Part #2SC3856
Click to expand...

Hey, okay i want to attempt to repair my brothers old Sony receiver that has a blown output transistor (even the others could be shorted) and theres couple of small resistors that are burned. The out model are C3856 SK and A1492 SK. This is something i've never tried and this radio has alot of screws to get off. So any help would be appreciated. Thanks
 
#43
Semi dealers

Hiya,
for people in need of output trannies in the states try:

B&D Enterprises: Part #2SA1492
B&D Enterprises: Part #2SC3856

That's a web based shop with a $15.- min. order and they have got the original widely used and very good Sanken Parts (for a good price to).
The SOA is quite remarkable for these parts claiming to be 'just' 130W. Other manufactures would not hesitate to claim more...
Sanken did one of the 1st really well accepted high power TO-3 transistors in the form of 2SA909 and 2SA1586.
If the output tends to 'blow up' in this amp, it's most likely to be a topology issue more than the output devices...

Cheers:drink:
a1greatdane
 
#46
Hello,

I have a DENON PMA-1520 with blown output transistors

The original parts are Sanken 2SC3856 and 2SA1492.

Can i replace them with toshiba 2SC5200 and 2SA1943 ,
or should i use replacements as RCruz suggested ?

Later, when i have some money i will order sanken from bdent.com,
but at the moment the toshibs would be perfect because of price and i can get them instantly.

Waiting for your opinions 🙂

Thanks

Paulius
 
#47
AndrewT, I found this thread and have read through the advice here. It's been a God send. Thanks.

I have a 5-channel amp - a Rotel RB985 - which has a channel dead. It took me a while for find info on these Sanken transistors (SK A1492/C3856). My question really is about what other components I might need besides the transistors to complete the repair. I know that's a "How long is a piece of string" question, so let me put in some background...

1st off, I'm not an electronics engineer (hence the above question 😀 ) but I am comfortable replacing to component level.

The amp is old, circa mid 90's, so as well as fixing the transistors I'm going to take the opportunity to recap it. The big 63V 10,000 and 15,000 mic caps are bulging.

Only one channel is down. It's blown the protection fuses. I did continuity tests across the terminals of transistors (2 each of 1492 & 3856, and one SK A1667 per channel) and again on the mirror image channels. I read resistance on the working channels. The terminals on the blown channel's transistors show continuity so they're obviously dead.


So, do you think I'm safe just replacing the transistors, or should I also be looking and testing elsewhere for semiconductors that have shorted?

Thanks in anticipation.
 
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#50
Those Rotels are nice amps, get it fixed, if your output transistors are blown your drivers and predrivers are probably too, shorted the outputs on the amp probably. Recap with the original caps, they are from BHC, available to purchase from the UK at around 12 pounds a cap, they are excellent caps and hard to beat. For a upgrade on the caps get from the same manufacturer the so called t network caps, more expensive but worth the cost. As for replacing those sankens I would suggest using Sanken 2sa2223,2sc6145, Ive used these now in repairing several Rotels and in diy projects and they are probably the best power BJTs money can buy.
 
#51
Hi, I know bringing a thread from the dead 😀 but I have a question? If I replace a higher rated output transistor inplace a of a lower power rated one? I put in C3856 and A1692 inplace of C4467 and A1694 because they were the only transistors I had. It plays good the receiver haven't had a problem so far. Any idea if it's good?
 
#52
Should be ok, depends on the circuit topology. The fT's and gains are within reason (well except the bigger transistor goes to a higher current as expected) and SOA is larger, so you shouldn't have too many issues if the output stage was an EF.

CFP on the other hand could cause issues with oscillation.
 
#53
mt490 said:
Should be ok, depends on the circuit topology. The fT's and gains are within reason (well except the bigger transistor goes to a higher current as expected) and SOA is larger, so you shouldn't have too many issues if the output stage was an EF.

CFP on the other hand could cause issues with oscillation.
Click to expand...

Yeah im using them in a kenwood stereo receiver class ab design has pot for biasing. I haven't noticed anything funny ever since i put those in. The new devices i put are rated for 180v 15a and originals were 120v 8a i think? I thought that maybe by putting them in mite change something.

Oh yeah the model of my receiver is KR-A4040
 
#55
Whilest I'm not trying to resurrect an old thread, I thought that this would be as good a place as any for this information.

A little digging in the interweb appears to reveal that the Samson S1000 is also sold as the Inter-M M1000 and Commax A1000 - I have one of the latter in bits on my bench at the moment, mostly dead.
At the time of writing (getting on for 10 years after the start of this thread) most of the transistors are unobtainable - notably the lateral FETs used in the driver stage. I've traced most of the power circuit (before I stumbled accross the schematic linked to earlier) and I'll be posting it online when complete.
The amp is not class G or H, but a pure class B; the unladen supplies on mine exceed +/-90v. Consensus here seems to be that this is asking too much of these little transistors.
I'm going to experiment with substituting different transistors (the FETs are going to be a particular problem, but I'm interested to see if a vertical FET will work) and I'll report my results either here or on the electro-tech-online forum.

Cheers all!
 
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