EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: madao on December 16, 2018, 04:18:42 pm
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Hi
I have a little trouble with Tektronix 568 + 230. Nixie show wrong after a bit time.
https://youtu.be/SKMouqQ_ZWY
Setting of curve tracer: 10V horz, 1mA vert.
This transistor is silicium, type 2N3877.
Massive thermal runaway with only 30mW power.
best regards
matt
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I have found a few transistors that develop collector to base leakage that looks similar to what you observe. Leakage increases at high temperatures and so as the transistor gets wamer, the collector current increases and the temperature increases and so on. The transistor should be replaced but you may find that a resistor between the base and emitter to divert the leakage current may help. I don't have the circuit so I can't say what value, but I would try 2K2.
That transistor is quite old and the processing or manufacture is not as good as more modern devices.
Cheers,
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correct, leakage between collector and base is reason for thermal runaway.
This transistor are driving by RTL logic-gatter, it should not be a problem. I'll replacing soon all 2N3877 by MPSA06. Why, because it is third failure of nixie drive transistor. (all three transistor have same failure)
best regards
matt