Arcam A70 SanKen SAP15 transistor trouble shoot

[MartyCan]

Hi everyone,

I'm new here and I'm not an electronic genius, but I've manage to repair a lot of things with logic. So I have that A70 that I purchased new and used mostly as a pre-amp. One year past warranty (of course) while turning it on, it goes red, then shuts off. It has the now known to be problematic Sanken SAP15 darlington transistors. There is no damaged or burnt component unlike some others have experienced. I do not trust the electronic shops around here as they did terrible job on 2 of my deck that I ended up repairing myself.  So does anyone here have experience with those Arcam? How do I diagnose those transistors? I hear the transistors are discontinued and a fella here found a way to make new ones fit. Any help is welcome! Thanks in advance!
 

[ambrosia heart]

 Buy a T4-LCR meter can help you  or check by scope with signal inputted and powered the amp section via transformer.  See photos.

[MartyCan]

That's a nice tool! Does it work with 5 legs darlington transistor as well? I don't have any of these tools, as an amateur, is it worth it to invest in them or should I bite the bullet at this stage and just ship it somewhere to a trusted shop, away from here and hope for the best? I also though that since the transistors are fairly cheap and are known to be problematic, and since there is no sign of "overheating" I could start by replacing them all and see what happens...  I was thinking of guetting myself a oscilloscope as it would be handy to find problems on my vintage fuel injection car, would that be any help with this as well?  Though?

Thanks very much!

[Audiorepair]

I've come across these in the past where the built in Emitter resistor has failed, but the transistor is otherwise good.
You can check for this with a multimeter across the appropriate pins.

So was able to bodge in an external resistor instead.


I don't like these things, just a problem waiting to happen IMHO.