Re: [CAD_CAM_EDM_DRO] BOSS stepper driver transistor

On Thursday 26 May 2005 06:49 pm, Polaraligned wrote:

> I lost one of my Z axis drive transistors. Probably because I am
> running a 208 volt machine on 240v. I found a tap to lower
> the voltage to all the electronics except the 3 phase transformer
> that powers the steppers. The other two axis have been running
> like a charm at 240v.
> The original transistor is a STA 7018. This crosses to a NTE 165.
> I have
> some 2N3055's handy. They are MUCH more hardy than the original
> transistors. Maybe by 10x in the power dissipation department.
> Can I use one of these? It exceeds the ratings of the original
> in every category. Suprisingly, all the transistor date codes
> on the machine match the time of manufacture. I thought these
> things were supposed to pop like popcorn?

Dunno about how they're supposed to pop, transistors have different failure
modes...

What supply voltage is this circuit operating at? I don't have data here on
the STA7018 (feel free to send a datasheet along to me if you have one) but
the 2N3055 is a 60V part, which makes me wonder.

The 2N3055 is a pretty common power transistor, but there are a LOT of
beefier parts out there these days.

How did the bad transistor fail? Open? Shorted? Something else?