unknown componet D977

Hi there
I am a complete novice to electronics of any kind but am proud to turn my hand to most things. I am current repairing an electronic spark generating unit for a motorcycle and have found a single component to be faulty.

I can find very little information on the particular componet.
Firstly it is in a TO220 package.
It has D977 written on it
the GND leg has been removed and is grounded through the heat sink bolt.

It has been suggested to me that it is a transistor used as a diode.

It has been suggested that the D number is a soviet naming system.
I either want to find a replacement part or find the specs so i can get a compatable.

thanks

Sounds like a Japanese device to me, you need to add '2S' to the front of it, so a 2SD977.

thanks nigel i will get on to it and have a look

Item found

Thanks again Nigel for your help.

It would seem that the offending component a 400A 6A Power amplifier. I have found a newer compatable version.

True thanks to some true experts most grateful..
Ross