Advice about repairing an IBM 5151

tony duell ard at
Tue Sep 1 12:57:35 CDT 2015

> Hmm, you are right, I am not seeing any spikes in voltage there. On
> the collector of the TR23 all I am getting as DC voltage is around
> 110mV. The oscilloscope tells me I am getting Vpp of about 4.4V with
> Vmax at 2.6V and Vmin at -1.8V and an average of 105mV (which matches
> what my multimeter tells me too).
> That sounds too low doesn't it?

That is far too low. 

Firstly, there should be a 12V or so feed to one pin on the flyback primary
winding (the winding that links to the collector of TR23). Is that present and 
correct? What about other components connected to that winding.

Are you sure TR23 is good. The horizontal output transistor in many monitors
often fails.


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