whats this transistor?

[pinballtoys]

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

[wraper]

It's certainly has ST logo, not Vitelic.

[wraper]

It's STBV42 https://www.st.com/resource/en/datasheet/stbv42.pdf

[Benta]

Yes, ST.
More likely a triac.

[wraper]

And you should have cleaned the part with alcohol. Since "B" in BV42 marking as basically invisible.

[pinballtoys]

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!

[Zero999]

Are the relays run off AC, or DC? That will enable to determine whether it's a TRIAC or BJT.

[pinballtoys]

looks like mains is half-wave rectified so assume its a transistor

 IMG_20220429_0002.pdf (514.46 kB - downloaded 34 times.)

[gamalot]

It's STBV42 https://www.st.com/resource/en/datasheet/stbv42.pdf

I seconded, it's definitely STBV42

[pinballtoys]

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