[Coco] Help: Magnavox 1CM135 Monitor

[KnudsenMJ at aol.com]

In a message dated 2/29/04 11:18:15 PM Eastern Standard Time, 
robert.gault at worldnet.att.net writes:

> > 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.

>  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.

No, I agree with whoever pointed out that the squeal means that the horiz 
output transistor is still working, and the flyback is probably good too.

Perhaps the extra squeal is because the flyback has lost its load and the HV 
is arcing over somewhere.  This could happen if the CRT's cathode heaters 
(filaments) went out.  I hope they didn't burn out, but you might check for the 
orange glow in the next of the tube that says they are lit.  If not, check for 
6.3 VAC on the tube socket -- may have a loose connection somewhere, since 
these boards are known for that.

Another possible cause is that the horizontal oscillator is running at too 
low a frequency, causing the output circuits and HV to not get what they need.  
This would also bring the frequency into a more audible range.

At least you can be pretty sure it's *not* the horiz output system, which is 
big bux if you can find the parts.  Let's hope it's not the CRT itself.  
--Mike K.