22 Jan
2017
22 Jan
'17
4:04 a.m.
On 22/01/2017 07:31, "Tony Duell" <ard.p850ug1 at gmail.com> wrote:
What do you mean by 'second output'? How many pins are used on this
'transformer'? If only 2 it is just a simple inductor, again possibly part of
a swtiching regulator.
There's 5 pins (5th for keying I guess) with 2 separate windings and I've
just realised the 2nd winding (destination -24V) isn't fed from anywhere.
It's only a 2 sided board and there are no top traces under the part.
There's also some incomplete traces in that circuit so I wonder if there
were planned enhancements for a Mark II that never happened. I'm marking up
the back of the board for my own understanding as I type.
It tests OK in my MOSFET tester.
It looks to be part of a switching regulator circuit.
Possibly to generate
other voltages from the 5V line. Can you post a picture of more of the PCB
around it.
Its second output goes via an IN4148 to the -24V regulator: The -24V
regulator can be seen just above the 4 blue caps, The regulator
that can be seen under the black wire is a 7812. The LF351N has -12V present
at its bias outputs, the opamp to its right has no markings helpfully.
What about that IRF523? That is a power MOSFET transistor and might well
be the chopper in the switching regulator circuit. Why do you assume the other 8 pin IC is an op-amp?
Initially because of the way it's wired but I'm checking it now. Once I've
marked up where the traces go the picture should be clearer.
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?