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.
I cannot see any bulging caps or burnt components, damaged traces or other obvious issues and I've looked very closely.
Someone suggested I check C914 - I know its 15uF but do you know the rating ??
Thanks for the tips.
I'm just concerned for the cause - it wasn't powered when knocked.
Perhaps it's just coincidence and it was a fault just in waiting ;-)
Dave
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On 16/03/2021 17:51, Ozan wrote:
Hi Dave,
I don't know if you already figured out the issue but in case you are still debugging: 63V at W972 translates to 48V at pin 12 of U940 which exceeds Abs Max of TL594. There must be other components that could be damaged permanently. In this state any powered up debug needs reducing the input voltage at pins 1 and 2 (input to pre-regulator) of sheet <7>, less than 55V but probably 45V is a good start. I would disconnect all the connectors to A1 board and supply external bench supply to pin 1 and 2.
Before doing electrical debug, I recommend visually look for broken solder junctions and reseat the ICs (if they are on a socket). Most likely in the pre-regulator section of sheet <7>.
If visual inspection doesn't show what is wrong electrical debug can identify the issue:
At 63V pre-regulator is not pulse width modulating the pass transistor or the load is too light. How does waveform (34) look like on sheet <7>?
Ozan
