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Old 2nd January 2005, 05:56 PM   #1
seahag is offline seahag  Canada
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Default to-92 general purpose

I have a busted amp here and found a few bad transistors.
they are very difficult for me to get.
I was wondering if anyone whould know a good replacement thats readily available?

here is the POS that blew.

PDF LINK

This might not be the place to ask.. but oh well..

Chris
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Old 2nd January 2005, 06:48 PM   #2
Eva is offline Eva  Spain
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This is actually the classic 2SA1266, try to search for this part number

It may be also replaced by BC556B, BC560C, BC557C, and dozens more...
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Old 2nd January 2005, 06:55 PM   #3
seahag is offline seahag  Canada
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I`m kinda limited to digikey for parts.
Its the easiest way to get parts to Canada.

Those dont seem to be available there.

I`m more interested in finding out how to choose one myself.

What are the parameters that I should be matching.
I see its a general purpose.. is that all I need and the amp rating ?


Thanks for the quick reply.
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Old 2nd January 2005, 07:19 PM   #4
jwb is offline jwb  United States
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Make sure you get a part with high enough max Vce, max Ic, approximately the same Vbe, and roughly the same Hfe. You'll also want to check the SOA to make sure it's appropriate for the amount of power the part is expected to dissipate. Finally you want to make sure the pinout is the same or reverse (ECB or BCE in this case).

Digi-key doesn't have a good selection of small-signal japanese transistors, you should check www.mcminone.com
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Old 2nd January 2005, 07:24 PM   #5
Eva is offline Eva  Spain
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Choose something with :

- Similar or higher Vceo. 45V may also do since these devices are not usually operated near its maximum Vce rating. Also note that higher Vceo devices usually show worse specs
- Similar or higher Hfe [look for 200 typ]
- Similar of higher Ft [look for 200 typ]
- Similar or lower Cob, It's low on almost all small signal devices
- Similar or higher Ic. However, devices rated at lower Ic may be also suitable since in practice these small signal transistors are usually operated below 10mA
- Similar or higher Pc. However, devices rated at less Pc may be also suitable if the original transistor didn't blow due to excessive dissipation and overheating

-Same pinout : Try to find devices with same ECB pinout as 2SA1266. Devices with BCE [reverse] pinout are also easy to mount by rotating them 180 degrees. Be careful since most European and American small signal TO-92 devices have either CBE or EBC pinout and will require leg twisting and a lot of patience for mounting
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Old 2nd January 2005, 08:02 PM   #6
seahag is offline seahag  Canada
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Thanks guys!

The cameout of a switching PS for a car audio amp.
they were located in the switching chip(TL49) circut board.

..
Thanks again.


Chris
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Old 2nd January 2005, 09:57 PM   #7
anatech is offline anatech  Canada
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Hi Chris,
Try 2SD667A or MPSA06. The leads have a different pinout on the MPSA06 . If this is driving a bunch of FETs I'll bet one or more went short. Check for that first.
-Chris
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Old 2nd January 2005, 11:16 PM   #8
seahag is offline seahag  Canada
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A06 is avail thu digikey.

I might have a few kicking around.

I thought the pwm did the switching. anyhow, the transistors are in the related circuts.. and yes a 2 of 2 went. :/
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Old 3rd January 2005, 12:02 AM   #9
seahag is offline seahag  Canada
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oh my.. the fets.. yes most of them fried along with thier resistors.

strangest thing. went out to go start the car and let it warm up.
10 mins later the truck was filled with that nasty smell.
wasnt even turned up.

A06 is a npn
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Old 3rd January 2005, 12:52 AM   #10
anatech is offline anatech  Canada
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Hi Chris,
Oops, right you are. Therefore you are looking at MPSA56 or 2SB647A.
Sorry about that.

Some equipment is not happy being cold. Esp. if you had condensation in there. Most parts are only rated for the consumer temperature range. If I recall, that would be 0 to 70 deg. Could be some caps when cold or a solder joint in the timing circuit around the TL494. Either way, the parts don't work when you let the smoke out.
-Chris
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