Electronics > Repair
Finding correct SMT diodes and transistors to fix my scope?
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rwgast_lowlevellogicdesin:
Im trying to fix the front end on one of the channels of my scope, from what I can tell the transistors and diodes in this pic are the problem... doing resistance and diode tests in circuit gives crazy values compared to the other three channels.



So far I have figured out one transistor is going to be a 2sk508-52 jfet, and it is definately bad, out of circuit a transistor tester reads it as 2 resistors!

The other three transistors labeled 3em with a sideways 4? are some sort of MMBTH10's but the sideways 4 is throwing me off I think they may be MMBTH10−04LT1G's but I am not sure.... The weird thing is in circuit only one leg of all three transistors was testing strange compared to the other three channels, using diode drop and resistance on a DMM, so I took them out. Oddly out of circuit diode drop/resistance tests doesn't work at all, the dmm says overload, but the transistor tester shows everyone with a VBE of 700mv and 6na IC.

The two diodes are labeled C1, I think they are NXP 43v zeners, but I'm not sure. I need to put my power supply back together because I don't have any other 50v source to test them with.
wraper:

--- Quote ---are some sort of MMBTH10's but the sideways 4 is throwing me off I think they may be MMBTH10−04LT1G's but I am not sure....
--- End quote ---
MMBTH10LT1G from Onsemi https://www.lcsc.com/product-detail/Bipolar-Transistors-BJT_onsemi-MMBTH10LT1G_C16204.html

--- Quote ---but the sideways 4 is throwing me off
--- End quote ---
Datasheet says date code orientation depends on manufacturing location.

--- Quote ---transistor is going to be a 2sk508-52 jfet
--- End quote ---
2SK508G-K52 to be precise.
rwgast_lowlevellogicdesin:
Any idea if those two c1 diodes above the jfet are NXP zeners?
wraper:
^Could be this https://www.lcsc.com/product-detail/Zener-Diodes_Nexperia-BZX585-B2V4-115_C503445.html
I suggest desolering one from a working channel if both of these are actually dead and checking if it's actually a 2.4V Zener diode. Multimeter might be enough for the test if it can measure a relatively high voltage in diode mode.
tautech:
@OP
I have some warranty replacement boards I can pull and test/check components if required.
Let me know the DSO models.
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