au-519 project/protection

thanks for the quick answer! i'll contact the local shop to verify if they can get this for me otherwise, i'll have to buy online! :)
 
okay so i installed the SRC, reassembled everything.. click! it works! checked dc offset, bias, all good. so I hook some speakers to it.. play music at maybe 25%, but one channel isnt playing too good so i wiggled the source selector pot and then no more music, protector blinks again, (at least it detected something) but now r41 is toasted and the power transistor are open. ugh.
 
damn that's not sounding good ...first things first did you get the pin-out correct on the scr ? if not that is what happened . if so you might have caused a short or who knows ..
first check you got the pin-outs correct then we can proceed .
 
I'm 99% sure the SCR is installed properly. I do have a picture, altho i don't seem to find the way to include it into my post other than hosting it myself somewhere on the web and <.img> it in my post. I am not very familiar with forums.

However, I highly suspect the output transistors I sourced locally to be the culprit. They just look 100% like the one I received from china, but they are both a little different from the one I pulled from the unit. I wasn't that suspicious first cause I thought, well they were most likely manifactured many years appart so they might have changed the silkscreen a little bit. But why would the same channel blow again if there was a short caused by the SCR and not the older set of transistor, which i would assume is somehow weaker since it has much more hours of work on it.. Anyway, now i am left with only chinese transistors, and I guess I don't reallly want to put them in. I'll try to find newer generation (not discontinued) to replace them so I can rule out the bad Transistors hypothesis.
 
makes sense it could be crap transistors in a few ways .. maybe just drawing some current through them was enough .
 
You could also consider NJW0302/0281.

Same packaging as the 1302/3281, slightly lower power rating but still sufficient, and most significantly lower capacitance (Cob).

Both types readily available from Mouser.

regards

Angus
 
They look like a good option also :thmbsp:

Hadn't spotted those before.

regards

Angus
According to their datasheet, they seem to be the same (or nearly the same) specs as the original Toshiba 2SA1962 & 2SC5242 - (with possibly just a little less max DC collector current? - according to the online Mouser table specs)
 
Finaly received my transistors !!!!!!!!!!!!!!! woot !
replaced the fried one and it works again! but this time it keeps on working. ugh im not buying shit from that local store again. Anyway, i tried to play with the settings (base and treble) and they do not seem to have any effect on the sound, i was using the aux input and speaker A. the loudness button works great (i do like how it sounds) but even if i turn it off the bass and treble knobs doesnt affect the sound. Can it be that it's too subtle to hear for untrained ears ? Also, its very very very loud, i dont think i could stand cranking it more than 33%. Anyway thanks for your help everyone i am sorry I took so long to reply but transistors were backordered.
 
is the tone switched on ? subsonic off ?
being loud is likely whatever your using as in cd player etc . could be a bit high output .
well done for getting it going again ..
p.s protection good now ?
 
yeah! >< my bad ... tone was on defeat...when i switched to on, guess what! it worked! i checked my ipod and the volume was pretty high so i guess thats it ! alright! thanks for all your support guys.. :)
 
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