monitor question (problem diagnosis)

Tony Duell ard at
Mon Nov 7 18:50:34 CST 2005

> I have a MAC Plus with the same symptom - seemed odd to me as well, so I asked
> a local guy who used to repair monitors. He didn't think it was that odd, here

I hate to say this, but you might want to suspect his comments in future!

> is what he responded with (I haven't had time to look further at it yet):
> >#2 - I've got a Mac Plus which displays a thin VERTICAL line - I've not 
> >seen this before, because since it has HV, the horizontal oscillator must
> >be running! - any guesses?
> This obviously has separate circuits for EHT and horizontal 
> drive/deflection, and the deflection circuit has a bad drive component or 

The Mac Plus has one output stage which drives the flyback transformer 
(EHT and other CRT voltages) and also drives the horizontal yoke. Trace 
out the schematic if you don't trust me :-)

But there is a very common problem with the Mac Plus that I mentioned in 
another message. The coupling capacitor fails and/or the contact on the 
yoke connector burns. IIRC the coupling capacitor was originally a 
non-polarised electrolytic, I normally fit a film capacitor there. 


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