VAXmate Flyback Transformer

Recently I fixed the power supply of my VAXmate, but found that there was a problem on the monitor board, which may be what caused the power supply to fail in the first place. My suspicion immediately fell on the flyback transformer, which is a common failure in vintage screen displays.

I removed it and tried doing a ring test on it to see if there are any shorted coils. Here is a picture of it, with the pins numbered, as close as I can tell, according to the description in the Figure 14-4 of the Technical Description.

Flyback Transformer

VAXmate flyback transformer from the monitor board with pins numbered

My probing with a multimeter suggests that pins 1-2-3-7 form one winding, and pins 5-6-8 form a second winding. This does, however, correspond to the pin numbers shown in the Technical Description.

My ring tests showed good ringing between the following pin pairs:

  • 1-2
  • 1-3
  • 2-7
  • 3-7
  • 5-6
  • 5-8

Where the ringing looks like this:

Flyback Good Ringing

Good ringing from the flyback transformer

I also saw some poor ringing between the following pin pairs:

  • 2-3
  • 1-7
  • 6-8

Where the ringing looks like this:

Flyback Bad Ringing

Poor ringing from the flyback transformer

I can’t be completely sure that the poor ringing means the transformer has failed because I don’t know how the transformer has been wound, and it could be a low number of turns in the particular part of the winding.

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