What wattage is the lamp in your dimbulb setup?
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On Sat, Mar 5, 2022 at 1:38 PM cslim388 <cslim388@...> wrote:
Hi James55,
This is a transformer based power supply. Take out the dim bulb. Measure
for shorts at the out put of every bridge rectifier without powering up. If
a short is found, then resolve that. Continue checking for shorts.
Power up without dim bulb to see if fuse will blow. If it does not blow,
then transformer is ok. Check output voltage of every bridge rectifier -
one of them may be faulty.
Cslim, 9v1cs
On 2 Mar 2022, at 10:57 AM, James55 <james_55@...> wrote:
?On Mon, Dec 13, 2021 at 02:39 AM, James55 wrote:
Hi all,
please excuse the lack of input, however I became deflated and just put
a cover over the scope and walked away.
Thing is, I really do need a working scope, so today decided to give it
another go.
The mains input is now running first through a dimbulb, which dutifully
illuminates when the unit is switched on. All of the low voltages rails are
close to zero. For example the 65v rail is up at a whopping 10.4v. The
minus 15 rail is 0.5v. The minus 8 is 0.4v and the 140v rail is 5.3v with
the 5v being shorted to ground at zero volts.
I removed the A5 Trigger, and A7 Timing, boards in the hope of
narrowing down the search area.
Things got off to a good start with the discovery of the shorted R1377
resistor, although that made no difference to any of the readings. There is
a pure short circuit on the 5v rail however for the life of me I cannot
seem to find it.
I have tested and tested all over the A6 and A10 boards, testing
voltages and also bell-testing for shorts with the power off. It really is
at the point where I can only see trees, without a glimpse of any wood...
I have also covered the board in IPA which all just sat there wet for
ages. There are no warm components, or even areas... I wish something would
just explode or at least go up in smoke, as I have no real idea as to where
else to look.
It did cross my mind that it might be the 5v rail 5500?f filter cap yet
although I only have a DMM it still reads 7000?f, so I am assuming it is
not shorted.
If anyone has any suggestions at all as to where I might check next
please feel free to chip in.
Perhaps I'll just leave it plugged in, as surely a direct short has to
start smoking at some point?
James
Michael A. Terrell