TECH : monitor field collapse

[P-Man]

[ukvac] TECH : monitor field collapse
hi all..

i'm in need of assistance, i was working on a b/w 13" monitor the other day,
it had a washed out picture, and was slightly off-kilter.. just the ticket
for capping it i thought. so i removed the monitor and replaced all the
electrolytics i could find, overkill i know, but hey..

anyway, re-installed it, and powered it up, i now have horizontal filed
collapse (thin white line on screen).

now, it wouldn't be so bad if there were schematics available for this
beast, but the monitor and tube are totally unlabelled, i'm assuming its
just some 70's jap crap.

now as i understand it, field collapse is when one of the oscillators goes
kaput, ie, the beam is not sweeping left->right to display horizontally...

now i don't believe i put a cap in the wrong way round in this thing, but it
looks like it had some repairs in the past for lifted tracks. i'm just
wondering if something bust while i was messing with it, thing is, i'm not
entirely sure where to start looking without schematics.. i assume the
IC-looking device is the oscillator, would i be correct?

let me know if you can help out, i'm pulling my hair out, the bloody thing
was working (albeit a bit crap) up until i had the bright idea to cap it...

let me know!

Andy

 

[John Bennett]

Re: [ukvac] TECH : monitor field collapse
In article <002501c090fc$9517d7e0$ccb1ff3e@hal9000>, Andy Welburn
<warlords@ntlworld.com> writes
>just the ticket
>for capping it i thought. so i removed the monitor and replaced all the
>electrolytics i could find, overkill i know, but hey..
>
>anyway, re-installed it, and powered it up, i now have horizontal filed
>collapse (thin white line on screen).

My first step would be to examine the back of the board extremely
carefully for misplaced solder streaks or dry joints, and triple check
the orientation of the caps. It's surprisingly easy to make a mistake
when doing a lot.

By the way I got the PCB OK thanks.

--
Clive Mitchell



DATA Imported from archives: originally posted by Clive Mitchell (clive@emanator.demon.co.uk)

 

[John Bennett]

Re: [ukvac] TECH : monitor field collapse
Thanks for the advice clive, found the fault .... just a 10p cap. Just about
to start fixing the tracks i cut to find the prob and instal the replacement
cap....here goes nothing!

l8er,
Nick.


DATA Imported from archives: originally posted by Nick Nethercott (n.nethercott@virgin.net)

 

[P-Man]

Re: [ukvac] TECH : monitor field collapse
> My first step would be to examine the back of the board extremely
> carefully for misplaced solder streaks or dry joints, and triple check
> the orientation of the caps. It's surprisingly easy to make a mistake
> when doing a lot.

despite Nick Nethercroft? posting a 'thanks and its fixed', alas, no, my
monitor still isn't fixed the problem is that this monitor is totally
unmarked, in a few instances, polarities aren't marked, and in some other
places, there were caps in the positions of resistors.

i went over the whole board last night, re-inforcing joints/repairing dodgy
looking tracks..

again, to no avail

the only thing i cab think of is that i put a cap in backwards, the fun bit
will be locating it, i did swap one round which i thought maybe wrong, but
it still made no difference, it was next to a v.hold pot...

it is most perplexing.. you see, i could now got hunting for a cap and mess
about with ALL the caps, only to find that it IS the oscilator that has
bust, in which case i will be chasing my tail (

well, i saved all the old caps, and by orientating the dirt on the caps, i
could work out which way they go round, but with so many caps of the same
type, i may come unstuck, but i'm willing to try anything

> By the way I got the PCB OK thanks.



> --
> Clive Mitchell

seeya!

 

[d-type]

RE: [ukvac] TECH : monitor field collapse
Andy,

Why don't you just replace the big oscillator IC just in case it
co-incidentally has died whilst you were dicking around in there? They're only
a few quid in most cases. Try Swallow, or if it's obscure, telepart.

I've fixed horizontal white line field collapses on a number of monitors by
just replacing it.

Phillip Eaton (D-Type/Flip-Flop)
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Tel: +44 (0)1536 504434/268424 Fax: +44 (0)845 334 8195
Email: d-type@phillipeaton.com Mobile: +44 (0)7775 726366
Web: www.phillipeaton.com
-------------------------------------------------------------------

>

 

[P-Man]

Re: [ukvac] TECH : monitor field collapse
> Andy,
>
> Why don't you just replace the big oscillator IC just in case it
> co-incidentally has died whilst you were dicking around in there? They're
only
> a few quid in most cases. Try Swallow, or if it's obscure, telepart.

A. the number bares no relevance to any IC i've been able to find otherwise
i would have replaced it already i'll try badgering some old tv shops and
stuff to see if anyones heard of it.

> I've fixed horizontal white line field collapses on a number of monitors
by
> just replacing it.

B. it is loss of horizontal deflection, there is a single white vertical
line (when looked at from a horizontal orientation)

> Phillip Eaton (D-Type/Flip-Flop)

andy

 

[Guests]

Re: [ukvac] TECH : monitor field collapse

> B. it is loss of horizontal deflection, there is a single white
> vertical line (when looked at from a horizontal orientation)

Well it won't be the chip then, as the same output from the chip is
used for driving the flyback transformer, and there would be no line
at all if there was no EHT from the transformer. I would trace the
circuit back direct from the scan coils, and see if there is a scan
coupling capacitor that is either open circuit, or inserted backwards.
(Should be quite a big electrolytic).

It is very unlikely to be an active component failure (IC, transistor)
as there isn't any that wouldn't of also killed the drive to the
flyback (except maybe for something used as part of an E-W correction
circuit). So you are looking for cap, resistor or inductor failure
(or the scan coils themselves).

Dave.
(Who's lost the original mail, and can't remember which monitor we
are talking about anyway).



DATA Imported from archives: originally posted by Dave Roberts (daverob@cwcom.net)

 

[P-Man]

Re: [ukvac] TECH : monitor field collapse
> > B. it is loss of horizontal deflection, there is a single white
> > vertical line (when looked at from a horizontal orientation)
>
> Well it won't be the chip then, as the same output from the chip is
> used for driving the flyback transformer, and there would be no line
> at all if there was no EHT from the transformer.

i read this on the randy fromm site, the only time he mentions horizontal
deflection loss, he talks about HT loss also.. which i do not have, that is
what puzzled me.

> I would trace the
> circuit back direct from the scan coils, and see if there is a scan
> coupling capacitor that is either open circuit, or inserted backwards.
> (Should be quite a big electrolytic).

yep, probably in backwards, but this is the prob, the board isn't polarity
marked by the caps. if i can isolate the caps around the scan coil output
section, i can try isolate it to a small number of caps (fingers crossed).

> It is very unlikely to be an active component failure (IC, transistor)
> as there isn't any that wouldn't of also killed the drive to the
> flyback (except maybe for something used as part of an E-W correction
> circuit). So you are looking for cap, resistor or inductor failure
> (or the scan coils themselves).

at least it gives me new hope that it might just be a cap.

> Dave.
> (Who's lost the original mail, and can't remember which monitor we
> are talking about anyway).

its some japcrap black and white 13" monitor unbranded, unmarked, the tube
isn't even marked either.. POS thing in an early b/w space invaders
cocktail. Its different from the last b/w moitor i had in an SI cocktail.
this makes the whole process harder

 

[PaulSwan]

Re: [ukvac] TECH : monitor field collapse
Andy,

If it's the same 13" B&W monitor that is used in the B&W Taito Space
Invaders Cocktail, I actually have a some silicon for it that I bought
but never used, including the osc. IC and a few of the trannys.

Vertical collapse should be straight forward to trace if you have access
to a scope. First thing I'd do is get out a multimeter, pen and paper
and trace out the circuit from the scan coil back to it's drive
transistors. Once the drive transistors have been identified, I'd get
the scope out and have a look at what was going on around them to see if
the problem is before or after the final drive stage.

Schematics for other B&W monitors of that era may help as they are all
functionally similar.

Good luck!

Paul.