hp-91 transistor substitution

[cruff]

(09-20-2014 10:20 PM)Paul Berger (Canada) Wrote:  From your picture that does not look like a break in the transistor, that looks more like there is a coating of some kind on the back.

To my eyes it looks like a catastrophic failure of the transistor caused the package to split apart. I've seen that happen with over voltage or other over heating. You can find Youtube videos of people killing various components that way. As others have suggested, this may indicate there is another problem that may aslo need to be resolved.