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Electronics => Projects, Designs, and Technical Stuff => Topic started by: pinballtoys on May 24, 2022, 10:55:23 am

Title: whats this transistor?
Post by: pinballtoys on May 24, 2022, 10:55:23 am
hello all
was looking to replace this transistor but not sure what to order?
i can see its made by Vitelic and looks to be an NPN with ECB pinout but I'm struggling to find its full part number
it switches a 240V relays and suspect a MPSA42 may do the trick but the pinout is different.

Anyone have some suggestions please?
Bob

https://www.dropbox.com/s/kcb7rakxpwdmziv/transistor%20%281%29.jpg?dl=0 (https://www.dropbox.com/s/kcb7rakxpwdmziv/transistor%20%281%29.jpg?dl=0)

Title: Re: whats this transistor?
Post by: wraper on May 24, 2022, 11:00:23 am
It's certainly has ST logo, not Vitelic.
Title: Re: whats this transistor?
Post by: wraper on May 24, 2022, 11:03:58 am
It's STBV42 https://www.st.com/resource/en/datasheet/stbv42.pdf (https://www.st.com/resource/en/datasheet/stbv42.pdf)
Title: Re: whats this transistor?
Post by: Benta on May 24, 2022, 11:04:19 am
Yes, ST.
More likely a triac.
Title: Re: whats this transistor?
Post by: wraper on May 24, 2022, 11:06:29 am
And you should have cleaned the part with alcohol. Since "B" in BV42 marking as basically invisible.
Title: Re: whats this transistor?
Post by: pinballtoys on May 24, 2022, 11:24:14 am
thanks so much
I'm in the UK and would normally buy from RS components, but it looks like this device went obsolete some time ago!
Title: Re: whats this transistor?
Post by: Zero999 on May 24, 2022, 12:20:02 pm
Are the relays run off AC, or DC? That will enable to determine whether it's a TRIAC or BJT.
Title: Re: whats this transistor?
Post by: pinballtoys on May 24, 2022, 12:26:23 pm
looks like mains is half-wave rectified so assume its a transistor

[attachimg=1]
Title: Re: whats this transistor?
Post by: gamalot on May 24, 2022, 12:30:41 pm
Quote from: wraper on May 24, 2022, 11:03:58 am
It's STBV42 https://www.st.com/resource/en/datasheet/stbv42.pdf (https://www.st.com/resource/en/datasheet/stbv42.pdf)

I seconded, it's definitely STBV42

Title: Re: whats this transistor?
Post by: pinballtoys on May 24, 2022, 12:37:51 pm
this is the circuit board I'm trying to repair, the problem being RLB is not switching on!

i thought i'd found the problem with capacitor C2 that had a high ESR but fitted new cap and problem persists
not sure how this works?
i can see that RLA is permanently on and even though half-wave supplied C1 ensure it stays on