Hiya, me again!

I've got a laser level which has stopped working, i took the main board out and there was a S8550 transistor that when the board was powered, was running at a toasty 220c.

It looks like either that has caused the laser diode driver to fail or vice versa, there is what I think might be a TVS that has failed on the PCB for the laser diode.

The markings from what I can see are either: SGC or S6C

The measurements of the component are:

H: 1.95mm
W: 1.9mm
L: 3.4mm
Length is not including solder and are approximate as I'm only using some cheap digital calipers.

I think this is a 1SMA28ACAT3G and I think that makes sense given it's positioning on the diode driver, but I'm not certain.

I've attached some photos, if anyone who's better at this than I am could give me their two penneth I'd appreciate it.

 

Yes, this is a TVS. However, they are very robust and I haven't seen any died on the laser drivers. Most likely, this TVS is not needed at all, and can be removed for a time being. Also, the clamping voltage 45V seems too high for this circuit, you can use something like Vdd + 4V.
I would check the laser diode first, it seems to be fried/shorted. If the ohmmeter shows <2 oHm - it is fried.
P.S. The soldering on the PCB is awful

 

Yes, this is a TVS. However, they are very robust and I haven't seen any died on the laser drivers. Most likely, this TVS is not needed at all, and can be removed for a time being. Also, the clamping voltage 45V seems too high for this circuit, you can use something like Vdd + 4V.
I would check the laser diode first, it seems to be fried/shorted. If the ohmmeter shows <2 oHm - it is fried.
P.S. The soldering on the PCB is awful

Morning, thanks for the response.

Yes I think all the boards in this level were hand soldered, it's from the early 2000s, so it's around 20 years old now.

I removed the TVS which had a direct short on it, the diode itself works as intended, I'll measure it out of circuit and see what the resistance is, 650nm diodes aren't expensive if it needs replacing, so that's a bonus I guess

I'll look at replacing the TVS just in case, the TVS that was in there is discontinued so I'll have to find something suitable.

Thanks for your time