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#1
Today, 05:31 PM
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transistor hFE testing higher than expected
I have a transistor 435-1 and the use case in the circuit is the video buffer leaving the IF/detector chip. The one in the TV tested at hFE 568. I have 2 others out of another chassis and looks to be different manufacturer but the number is the same. One tesed at hFE 286 and other tested at hFE287. The replacement for transistor is NTE123AP it's max hFE 300 at 150ma link https://www.alldatasheet.com/datashe.../NTE123AP.html . I think the original is bad as why would the recommend replacement be lower than OG part. I have not changed many transistors and ones I have tested shorted. I looked online but couldn't get a good answer to my question.
Last edited by liammc00; Today at 06:01 PM. 
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#2
Today, 07:34 PM
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hFE = 568 sounds uunusually high for a general purpose small-signal video transistor, but I don't suppose it can cause a problem. In most well designed transistor circuits it's only the minimum hFE that's of concern, and as a rule of thumb hFE = 100 is sufficient in most circuits.
It does disturb a bit that the spec sheet recommends this part number for audio applications. However, it may be that the transistor maker was trying to sell it for audio and the TV design engineer looked at the specs and the price and decided it was fine for video. Is this buffer stage an emitter follower, or is a signal taken off the collector?
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#3
Today, 08:15 PM
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The signal looks like it's coming off the emitter. I'm thinking I should just try one other 435-1 transistors as both them test basically the same. The part is probably fine but since it's pretty easy test why not. The part is fine back to the drawing board. Thanks for the helpful information.
Last edited by liammc00; Today at 08:38 PM.
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