Leaking Transistors

latala · 14th July 2006, 11:50 AM

I am in the proccess of repairing /restoring a Harmon Kardon HK 1000 cassette deck and have come across an unusually high no of NPN plastic signal transistors that are leaky
the transistors are run at only 12 volts in this unit !!
the unit may run for hours and then a transistor will leak to such an extend that the signals are lost.
I passed an earlier comment re te HK 330 going faulty and may have misled Anatech and a few others sorry about that !
I am interested in this long term effect just to know what is happening any ideas ?
regards Trev

latala · 14th July 2006, 07:53 PM

Further to the posting the transistor ref is C458 and below that 3 (hitachie symbol)E
I am wondering if its plastic posioning I think I read in the dim past of this effect !
regards Trev

richie00boy · 14th July 2006, 08:54 PM

Now that you mention it I do recall hearing a theory of 'plastic poisoning' or rather migration of impurities from the plastic into the silicon. Difficult to say if that's what's happened to you.

cliffforrest · 14th July 2006, 09:15 PM

There was also a big incident with some contamination inside metal can devices called "Purple plague".

This was with Fairchild devices and I one changed hundreds of them in semiconductor testers.

But that was over 30 years ago ..........

anatech · 14th July 2006, 09:59 PM

Hi Trevor,
Now the clouds part and your problem becomes clear!

The 2SC458 is a flaky part. Everyone had trouble with them. I was doing Marantz warranty when those problems surfaced in the 22XX series receivers. Replace with 2SC1815 or 2SC1775A. Seldom are they run to their max current, so don't be too concerned over the lower current rating unless you know the circuit may require more.

Just yank them and replace, don't even bother to troubleshoot the bad ones. Replace them all.

-Chris

djk · 15th July 2006, 12:15 PM

Any 2SC1345E that you find in mid '70s gear is probably bad too.

anatech · 15th July 2006, 03:10 PM

Gee djk,
I didn't know that. Guess I haven't been bit yet. Thanks for the hint!

-Chris

14th July 2006, 11:50 AM	#1
latala diyAudio Member Join Date: Feb 2006 Location: staffordshire	Leaking Transistors I am in the proccess of repairing /restoring a Harmon Kardon HK 1000 cassette deck and have come across an unusually high no of NPN plastic signal transistors that are leaky the transistors are run at only 12 volts in this unit !! the unit may run for hours and then a transistor will leak to such an extend that the signals are lost. I passed an earlier comment re te HK 330 going faulty and may have misled Anatech and a few others sorry about that ! I am interested in this long term effect just to know what is happening any ideas ? regards Trev

14th July 2006, 08:54 PM	#3
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Now that you mention it I do recall hearing a theory of 'plastic poisoning' or rather migration of impurities from the plastic into the silicon. Difficult to say if that's what's happened to you. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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14th July 2006, 07:53 PM	#2
latala diyAudio Member Join Date: Feb 2006 Location: staffordshire	Further to the posting the transistor ref is C458 and below that 3 (hitachie symbol)E I am wondering if its plastic posioning I think I read in the dim past of this effect ! regards Trev

14th July 2006, 09:15 PM	#4
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	There was also a big incident with some contamination inside metal can devices called "Purple plague". This was with Fairchild devices and I one changed hundreds of them in semiconductor testers. But that was over 30 years ago ..........

14th July 2006, 09:59 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Trevor, Now the clouds part and your problem becomes clear! The 2SC458 is a flaky part. Everyone had trouble with them. I was doing Marantz warranty when those problems surfaced in the 22XX series receivers. Replace with 2SC1815 or 2SC1775A. Seldom are they run to their max current, so don't be too concerned over the lower current rating unless you know the circuit may require more. Just yank them and replace, don't even bother to troubleshoot the bad ones. Replace them all. -Chris

15th July 2006, 12:15 PM	#6
djk diyAudio Member Join Date: Feb 2001 Location: USA	Any 2SC1345E that you find in mid '70s gear is probably bad too.

15th July 2006, 03:10 PM	#7
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Gee djk, I didn't know that. Guess I haven't been bit yet. Thanks for the hint! -Chris

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