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Troubleshooting TI 99/4A QI video RAM


lgallair

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Between 1,2 - 8.5vac approx.(unloaded)

 

Between 2,3 - 19.3vac approx.(unloaded)

 

Between 1,3 - 27.8vac approx.(unloaded)

 

...so, pin 2 is center tapped.

 

The numbers on the plug are in a different order.

 

Not sure how that "3. Red 5 volt" reading was arrived at!

A reading of 5vac between pins 1,3(loaded) would indicate that one of coils in the xfmr. has been wired out of phase(inverted).

 

This would cause the 7905 in the diagram to load the wrong alternation.

Though seemingly insignificant, this could result in different thermal coefficients.:twisted:

Edited by HOME AUTOMATION
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