Iiyama 21" vision master monitor crackling noise

[Jules]

Over the last couple of weeks my Iiyama 21" Vision Master (MT-9021)
monitor's started making a series of sharp crackles when being turned
on or off, and occasionally it's completely lost picture for a fraction of
a second (also accompanied by a loud crack).

Certainly sounds like something's arcing where it shouldn't be - I'm
pretty sure the noise isn't coming from any of the relays. There's no
visible arc though in a dark room with the case off when the screen's
turned on or off.

Internal short in the flyback? Any common failure points in these
particular displays related to these sorts of symptoms?

The display seems to be having voltage regulation trouble too - there
seems to be quite a bit of 'bounce' when changing from a dark to light
screen. Unfortunately I can't be certain that it wasn't there before these
HV troubles started.

No sign of bulging / leaking caps, but I haven't got to the point of doing
any real tests yet - thought I'd ask group wisdom first!

cheers

Jules

 

[Mr. Land]

You've watched the chassis with the cover off in a darkened room and
can't see any arcing? How about the board plugging into the tube? G2
arcing perhaps?

 

[Jules]

You've watched the chassis with the cover off in a darkened room and
can't see any arcing? How about the board plugging into the tube? G2
arcing perhaps?

Nope. There are a few occasional mild-looking arcs from the yoke clamp
screw - apparently to the yoke body itself - when the monitor's turned
off. I'm not sure what to make of those - they're not in sync with any of
the louder cracking noises (and don't happen nearly as often) so are
presumably either a secondary effect of whatever the main fault is or just
natural discharging from shutting off (may always have been there for all
I know)

The monitor's a bit dusty inside, although I've seen far worse - I'll give
it a good blast with an air compressor later I think and blow the dirt out
just in case that is the problem (plus also check any grounding points etc.)

I can pick up a spare 19" screen tomorrow which at least means I can take
my time diagnosing the problem with this display

cheers

Jules

 

[John K]

Jules? From a dot f?

 

[Jules]

Jules? From a dot f?

sorry to disappoint, but no

cheers

Jules

 

[Jules]

The monitor's a bit dusty inside, although I've seen far worse - I'll give
it a good blast with an air compressor later I think and blow the dirt out
just in case that is the problem (plus also check any grounding points etc.)

Hmm, well no luck - same problem.

I'm tempted to remove the flyback and check for signs of arcing
underneath (in which case a repair that'll hold *might* be possible), but
it's looking like I need a new flyback...

Without the service manual, the only labelled test point is 130V just
downstream of the PSU - that's sitting at 128V on my display, which is
*probably* within tolerance (there is a pot to adjust it, so I'll try
tweaking it slightly just in case)

cheers

Jules

 

[Mr. Land]

Pardon if this is a stupid question but did you try any Internet-wide
searches using the monitor model number?

I did this just for fun with a recent monitor I had that went dead, and
was shocked to find a site that had the full schematic for download for
free.

Using that I was able to locate a burned-out $3 SCR and the monitor's
back in service.

Hope you have equal luck...