[Coco] Help: Magnavox 1CM135 Monitor

[Robert Gault]

Boisy G. Pitre wrote:

> I have a Magnavox 1CM135 RGB/Composite Monitor - this thing was working 
> great, then all of a sudden stopped.  Now there is no picture.  Just a 
> constant, high pitch squeal when you apply power.
> 
> Can any of you Monitor guys (Gene Heskett?) provide some insight as to 
> what possibly may be wrong?  I don't have much expertise on diagnosing 
> monitors, and before I pitch it to the curb, I want to make sure it 
> isn't something simple or easy to fix.
> 
> Boisy
> 
> 
> 
> 
> 
If you hear it as a "high pitched squeal", it pretty much has to be the 
15KHz circuit. The transformer could be heard if the plates have gotten 
loosened on set like this but that normally did not prevent it from working.

Most likely thing is a blown output transistor in the horizontal 
circuit. However, without a circuit diagram including voltage points and 
wave forms, it is going to be difficult to diagnose your set. You will 
probably need an oscilliscope and educated guessing at the type of 
waveforms that should be present within the horizontal circuit. Back 
track from the output transistor until you find a waveform. The 
transistor that separates the waveform from the blank portion should be 
the culprit.