Update :-
Q923 (TIP30C) is indeed a 3 pin short <1 Ohm in all 3 directions.
Also
Q913 (TIP31C) is essentially just a double diode with no gain
Q912 is OK
Q950, and Q960? (both TIP30C) are OK
C914 reads as 12uF with an ESR of 1.2 - is that reasonable ???
I have ordered replacements (+ spares) - probably not much more I can do until they arrive.
Thanks very much for the help so far?:-)
Regards,
Dave
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On 16/03/2021 20:29, Ozan wrote:
I have identified that Q913 is short circuit between E,B&C and I also
suspect Q923, but until I get them out that's as far as I've got.
Shorted Q913 could cause what you saw. However, did you measure it in place or after disconnecting from the circuit?
Someone suggested I check C914 - I know its 15uF but do you know the
rating ??
All component information is in the service manual. Section 8-9 (Page 113 in the PDF I am looking at) shows 15uF, 20%, 63V. I don't see why it would cause this issue after a knock but now all the components (including caps) did exceed their expected voltage by a large margin so they could be damaged. For example C971 is rated 50V but was stressed to 63V. Some components will survive brief over voltage, some may be damaged. In particular ICs may go into "latch up" and draw excessive current.
Ozan
Ozan
