Mag 986FS CRT shimmering picture - schematic?

[Jules Richardson]

Anyone happen to have a schematic handy for a Mag 986FS / 986N 19" CRT
monitor? (Probably also rebranded by Gateway at one of theirs, although I
know their EV900 is a different animal).

I was given one the other day where the picture seems to shimmer, at
least in part dependent on changes in the screen contents. I can trace
out the schematic for the PSU section and go from there if I have to, but
having a genuine schematic would be a lot nicer to have!

(I've got a 19" CRT on one machine which has a weak tube, so this would
be a nice replacement if I can get it running)

cheers

Jules

 

[Sjouke Burry]

Jules Richardson <julesrichardsonnewsmoo@gmail.com> wrote in
news:khkid4$rqg$1@dont-email.me:

Anyone happen to have a schematic handy for a Mag 986FS / 986N 19" CRT
monitor? (Probably also rebranded by Gateway at one of theirs,
although I know their EV900 is a different animal).

I was given one the other day where the picture seems to shimmer, at
least in part dependent on changes in the screen contents. I can trace
out the schematic for the PSU section and go from there if I have to,
but having a genuine schematic would be a lot nicer to have!

(I've got a 19" CRT on one machine which has a weak tube, so this
would be a nice replacement if I can get it running)

cheers

Jules

Sounds like a weak powersupply, and/or High voltage supply.
Check for bad components around there.

 

[Cydrome Leader]

Jules Richardson <julesrichardsonnewsmoo@gmail.com> wrote:

Anyone happen to have a schematic handy for a Mag 986FS / 986N 19" CRT
monitor? (Probably also rebranded by Gateway at one of theirs, although I
know their EV900 is a different animal).

I was given one the other day where the picture seems to shimmer, at
least in part dependent on changes in the screen contents. I can trace
out the schematic for the PSU section and go from there if I have to, but
having a genuine schematic would be a lot nicer to have!

(I've got a 19" CRT on one machine which has a weak tube, so this would
be a nice replacement if I can get it running)

cheers

Jules

Open it and look for bad caps by the power supply.

That's all I've ever had to replace on a Mag.

 

[Ian Field]

"Cydrome Leader" <presence@MUNGEpanix.com> wrote in message
news:khlihs$jlr$1@reader2.panix.com...

Jules Richardson <julesrichardsonnewsmoo@gmail.com> wrote:


Anyone happen to have a schematic handy for a Mag 986FS / 986N 19" CRT
monitor? (Probably also rebranded by Gateway at one of theirs, although I
know their EV900 is a different animal).

I was given one the other day where the picture seems to shimmer, at
least in part dependent on changes in the screen contents. I can trace
out the schematic for the PSU section and go from there if I have to, but
having a genuine schematic would be a lot nicer to have!

(I've got a 19" CRT on one machine which has a weak tube, so this would
be a nice replacement if I can get it running)

cheers

Jules

Open it and look for bad caps by the power supply.

That's all I've ever had to replace on a Mag.

Good place to start - assuming its a colour monitor, a faulty degauss system
can also cause picture shimmer.

Most monitors use a 2-pin posistor with a relay to take it out of circuit
after a delay - a welded contact would cause it to continue drawing residual
current through the degauss coil.

Some monitors used the same 3-pin dual posistor as TVs - 1 posistor in
series with the degauss coil and the second one direct across the AC mains,
that heats the deguass element so it doesn't draw current - a failed heating
posistor can cause shimmer.

 

[Jules Richardson]

On Thu, 14 Mar 2013 21:42:25 +0000, Ian Field wrote:

Open it and look for bad caps by the power supply.

That's all I've ever had to replace on a Mag.

Good place to start

Well... it is looking like caps. There weren't any that were showing
visual signs of failing, but then of course that's often the way. Sadly
my ESR meter's 4,500 miles away (so I've put it on the to-do list to buy
another).

Anyway, I've replaced the PSU's main smoothing cap and those on the
outputs of the 104V and 52V lines using parts from the junk box (which
aren't necessarily in the best of shape themselves!), and - so far - that
seems to have just about cured things; there are some *very* slight signs
of picture instability when scrolling display contents, but far better
than before and certainly at a level that I can put up with. I'll give it
a week or two and if it's still OK I'll order some new replacement caps.

Thanks for the replies, everyone!

cheers

Jules

 

[Ian Field]

"Jules Richardson" <julesrichardsonnewsmoo@gmail.com> wrote in message
news:ki393n$683$1@dont-email.me...

On Thu, 14 Mar 2013 21:42:25 +0000, Ian Field wrote:
Open it and look for bad caps by the power supply.

That's all I've ever had to replace on a Mag.

Good place to start

Well... it is looking like caps. There weren't any that were showing
visual signs of failing, but then of course that's often the way. Sadly
my ESR meter's 4,500 miles away (so I've put it on the to-do list to buy
another).

Anyway, I've replaced the PSU's main smoothing cap and those on the
outputs of the 104V and 52V lines using parts from the junk box (which
aren't necessarily in the best of shape themselves!), and - so far - that
seems to have just about cured things; there are some *very* slight signs
of picture instability when scrolling display contents, but far better
than before and certainly at a level that I can put up with. I'll give it
a week or two and if it's still OK I'll order some new replacement caps.

Its worth seeing how many caps run hot after replacement as well as when
determining which ones need to be replaced.

The ones that get hot obviously won't last long - sometimes you can take the
edge off the ripple current with a polycarbonate on the print side (in
parallel with the electrolytic).