The resistor did the trick and dropped the 5V rail to the expected value, so I worked through the cut links reconnecting each in turn and checking the voltages and total current.
The little beauty seems to be all OK running from the external supply for a range of simple tests.
More testing required and I have yet to go back to the line transformer/rectifier but looking hopeful.
I am still concerned that I haven't found a definite cause, I guess it might be the line board ...
Thanks for all the help guys.
Dave
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On 22/03/2021 20:44, Ozan wrote:
As Dave wrote this could be because of missing load at W991. Does adding a 470-ohm 0.5W to ground from W991 reduce it to ~ 5.2V?
Ozan
On 22/03/2021 17:55, David Slipper wrote:
EDIT: U9028 should be U902A/B
Dave
On 22/03/2021 17:18, David Slipper wrote:
OK I replaced Q913 and Q923 and I'm using an external supply of 45V
I have isolated W984, W987, W989, W972, and W991
W972 reads 35V
W984 reads 95V
W987 reads 8.5V
W989 reads -8.5
but W991 is showing 11V
I suspected Q921 but it seems to be OK.
I guess the next suspect is the LM358 in U9028 ???
The inverter stage seems to be working OK but I'm mystified by the 5V
rail at 11V !!
Any suggestions welcome.
Dave
On 17/03/2021 16:09, Ozan wrote:
C914 reads as 12uF with an ESR of 1.2 - is that reasonable ???
It is a bit low in capacitance but it is not the reason for the failure.
However, I would replace it anyway since you removed it and it was stressed by
high voltage.
Ozan
