Electronics > Beginners

[Closed] Flyback transformer testing and replacement

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floobydust:
It would be easier to take measurements using VSS as multimeter common. Otherwise it is confusing because GND is actually going to the output of IC5.
At "A" you need enough DC voltage for the regulators - at least 2V above their output rating.
SC17710YDA (3V)
SC17710YHA (1.5V)

So at minimum 5VDC needed at "A" so "B" will go up to 6Vp (due to D6 voltage drop). I would guess 7-9VDC is used.
If you start a repair thread with the model number, more people can help.

gkmaia:
When I was drawing the current flows that looked very confusing. Why having a voltage regulator that sends 1.5v back to T1?

I will do that, just a bit afraid of people thinking that is just myself asking the same question twice. If you think that is cool i will do it. I am new here so don;t want to get people upset.

Ian.M:
Uh Oh! .
I did say at the beginning "If the transformer is bad, it will usually show visible signs of distress, e.g. discoloured insulation from overheating".  In your new thread ( https://www.eevblog.com/forum/repair/finding-a-replacement-for-an-undocumented-transformer/ ) you posted this photo:

which clearly shows at least one badly burnt winding on the transformer.   Chris Leyson thinks its dead, and I agree.

Options at this point, include obtaining the OEM part, maybe used off a donor board from the same device if the manufacturer cant supply spares, rewinding the burnt windings in situ, hand winding a new transformer on a suitable core (but that requires a *LOT* of very careful deconstruction and testing to establish the core characteristics and gap, and a fair degree of craftsmanship), or patching in an off-the-shelf isolated DC-DC converter.

I strongly suggest that you only maintain *ONE* forum thread for this repair going forward.  Its up to you which one you wish to continue, but please post a notice and link to the other thread in the thread you want to close.

gkmaia:
Ok! how does the notice works? Is there a section in the forum where I can post it?

bsfeechannel:

--- Quote from: TheNewLab on January 06, 2019, 06:17:14 am ---OK, This isa my domb questions day...

I thought a flyback transformer is that thing you find in older TVs that are ussually round like an automobile coil..(TV is a little smaller. That has 4,5, 0r 6 usually, round outlets coming out of the tops.

IF that is not a flyback transformer, What on earth is it???

--- End quote ---

The origin of the flyback transformer is the TVs.

It is said that they got that name because, in TVs, they are part of a circuit responsible for the horizontal deflection of the electron beam in CRTs. The inductance of their primary together with the capacitance of the so called retrace capacitor (a.k.a. safety cap) determines the fly-back pulse duration, which controls the rapid return of the blanked beam back to the left of the screen.

It is also used to generate extra high voltage and other voltages for the CRT.

When the first modern SMPS were invented, one of the topologies used by the designers was exactly the already familiar flyback circuit. The components were available from the shelf.

But I suspect that the other topologies, buck, boost, etc. were also inspired by the flyback circuit somehow.

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