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Old 31st May 2006, 07:54 PM   #1
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Default mosfet getting hot !!!

Hi,

I have an amplifier and it has 4 mosfets which are paired (2sc3182 & 2sa1265) after a while 1 pair of these mosfet are getting hot the others get normal hot. can somebody tell me how to adjust the quescient current and how to calculate it or what is wrong please ?

thanks
ronald
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Old 31st May 2006, 07:59 PM   #2
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... schematic diagram?
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Old 31st May 2006, 08:26 PM   #3
MikeW is offline MikeW  United States
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Are they MOSFET or Bipolar?
http://www.cpcares.com/pdf/2SC3182.PDF
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Old 1st June 2006, 07:28 AM   #4
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i think they are MOSFET.

no i dont have chematics !
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Old 1st June 2006, 07:46 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
is that a two channel (stereo) amplifier?

One pair of output devices in each channel?

Compare the hot channel to the cooler channel.
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Old 1st June 2006, 10:22 AM   #6
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by djronbxs
i think they are MOSFET.
no i dont have chematics !
You may think what you want, but they are not.
MikeW gave you a polite hint, and even provided you with a datasheet link, I'll give you a less polite one: 2SA, 2SB, 2SC, 2SDxxxx are all bipolar transistors, marked according to japanese standards (JEIA). 2SA and 2SB are PNP, 2SC and 2SD are NPN. Under the same standard, (MOS)FETs are marked 2SJxxxx (P ch) and 2SKxxxx (N ch).
Poking inside amps without knowing the basics is asking for trouble!
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Old 1st June 2006, 12:00 PM   #7
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yes it is a stereo amplifier, with a pair on each side.

it is not getting very hot when idle but when i play for a short time it gets hot !

how can i measure the quiscent current please ? i have digital meter.


thanks
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Old 1st June 2006, 12:32 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
it is not getting very hot when idle but when i play for a short time it gets hot
that seems a bit odd.

I cannot see a quiescent adjustment curing this problem.

Could it be severe instability? causing hiFreq oscillation?

Or,

could there be a short on the output lead that carries current only when signal is amplified?
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Old 1st June 2006, 08:45 PM   #9
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what you mean ? why it isnt quiscent current prob ?
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Old 1st June 2006, 09:01 PM   #10
anatech is offline anatech  Canada
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Hi djronbxs,
AndrewT is right. If it was a quiescent current problem, the transistors woud get hot while idling (quiescent state). It does appear to be a load related problem.

Have you tried swapping the speaker leads (amp turned off!).

-Chris
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