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crispycircuit 19th November 2012 03:06 AM

Output subs for 2sa1301 & 2sc3280
My Yamaha Ax 500u integrated output transistor shorted. I have 2sa1302 and 2sc3281 in stock or what would be a better replacement of the transistors in the title line? The power supply is -+57v ...

panson_hk 19th November 2012 03:20 AM

Do you have pictured of the original parts? Are they TO-247 as 1302/3281? I guess so. Are you sure no other parts failed?

I like 1302/3281, but beware of fake parts.

crispycircuit 19th November 2012 03:30 AM

They look exactly the same. They're out of working amp. And I would test them.....

Ian Finch 19th November 2012 04:48 AM

Hi Crispycircuit. Did you locate a schematic with legible voltages? Being printed in red, many scanners seem to miss these, but it might be useful to share the source if you found a way around the problem.

Any Toshiba 2SC3280,81 or 2SA1301,02 manufactured after Toshiba made them obsolete in 2000 will be fakes. The complements were, of course, in different colours. Fairchild officially made some clones after that date but the only reliable source now is On-Semi MJL3281, 1302 and several variants like 4381,0381 MJW, NJW etc. by case type, thermaltrak diodes, Vceo etc. from an authorized agent or direct.

It's probably a good idea to use the spares from other equipment but are you sure the driver transistors are OK? If not, you could just wind up with more dead output transistors and 0 working amps.

crispycircuit 19th November 2012 05:01 AM

No luck finding voltage references in red. I wondered why they didn't show on the schematic. The rest of the schematic is good. I'm able to compare to the good channel. But finding the beginning and the end of the trouble is gonna be difficult for my skills. I did find voltages very high in the driver section but need to find what's causing the higher voltage. I'll replace the drive transistor as you recommend...

crispycircuit 19th November 2012 05:16 AM

I really don't want to live up to my name..............

Ian Finch 19th November 2012 07:21 AM

Our experience as DIY electronics dabblers can be measured by the size of our Semi graveyard.
When you go back and read the tombstones, you know you learned something important there :D

I was looking at the specs of the amp. and realised that with 57V rails, just how hard that single
pair of transistors can be pushed. You can see that it's not rated for 4R loads and only specified
a little higher at 4R than 8R. I wouldn't use it on 4R speakers except with careful use of the loud
knob, as the transistors would really only be reliable up to a continuous 85W on a typical heatsink.

All the same, they're great transistors and Yamaha built much of their reputation with them.
I imagine the AX500 will sound great too.

crispycircuit 20th November 2012 02:27 AM

Switching Diode sub....???
I found a glass diode Jap #1ss133. It has 57v on one side and 43v (bad channel) The good channel has 57v and 1.8v on the other side. What could I sub for that switching diode?

wahab 20th November 2012 03:05 AM

1N4148 is a good replacement , even slightly better than the original.

crispycircuit 20th November 2012 03:15 AM

I have some here. Let's see what happens....

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