Gareth Magennis wrote:




Anyway, it turned out Q7 was leaky, causing Diode string D23/24/25 to
conduct, presumably via Q26 CB junction, D40, and off to the amps output.
This turns on Q4 and Q5 MJE devices, causing the output to swing positive..

This one single SOT device cost just short of £5 on Ebay, via the only
seller I trust outside Farnell and RS.


** Hmmmm, Q7 has an innocent, TO92 looking number ( 2SC3645) but turns out to be a bit special:

https://www.promelec.ru/pdf/2SA1415-2SC3645.pdf

Finding leaky BJTs is a real PITA but you persisted and got there.


..... Phil