On Apr 3, 2018, at 3:48 PM, Phil Blundell via cctalk <cctalk at classiccmp.org>
wrote:
  On Tue, 2018-04-03 at 21:07 +0100, Ian Frost via
cctalk wrote:
 Recently booted up my B&W Powermac G3, all came up fine including the
 17? CRT monitor. However after a second or so, the
 monitor gives a ?popping? sound and the image on the screen expands
 then shrinks. This repeats every few seconds.
 I?m guessing the monitor is on the way out - but as this is a
 complete B&W system - I wondered what the likely cause is? 
 That sounds like
some sort of problem with the EHT supply.  
 
https://en.wikipedia.org/wiki/Apple_displays
indicates:
?.The Apple Studio Display series of CRT displays were available in a 17" Diamondtron
and a 21" Trinitron CRT, both driven by an LG-Manufactured chassis. These displays
were notorious for faulty flybacks. ?
</instant wikipedia expert >[
Would that be consistent with the symptoms, and is there a good way to test?
                                                - Mark