While waiting on parts for the current source I've been messing with the +13.5V - replaced all the transistors in that area and get the correct voltage at no load (well, marginally over). I reconnect the tuner feed, this time with my DMM connected ready. Initially voltage is correct but rapidly decays. I quickly switch off to avoid damage.
I decide to connect a 100 ohm resistor as a dummy load. Voltage is okay at around 13.5V for around 30 seconds, then suddenly jumps up to 14+V, then violently to zero and back a few times, presumably as something goes into its death throes.. at least it looks like the tuner board is off the hook.
So, is there anything else that could be doing this? I see there is a link across to the +80V regulator but I don't know what this is for. I don't want to muck about doing the current source mod if I've got another unrelated issue that I can't solve. Thinking of just giving up now and getting the all singing all dancing replacement board.
Q201, 202, 204 were subbed for KSC945
Q203 & Q205 were subbed for on semi D44H11G.
Original failure mode was R202, Q201, Q202 & D207 toast.
TIA