TECH: Hantarex MTC900 anode cap replacement

[chadsarcade]

[ukvac] TECH: Hantarex MTC900 anode cap replacement
One for all you Monitor techs out there:

I've got a Hantarex MTC900 monitor which works great when the ambient
temperature is warm, but when cold the anode cap arcs like crazy. The
anode cap itself seems to be quite inflexible and doesn't seal well
when it's cold. I know silicone grease (or "anode cap goo" ) might
well sort this but I'd prefer to replace the cap with a new one if
possible.

Now, a new flyback unit will obviously sort this too, but whilst
flicking through CPC for one I saw they stock a replacement HT lead
which looks the same and replacing just that would be the preferable
(easier and cheaper) option.

The problem is that the MTC900 has a rather unusual arrangement in
this area - the HT lead from the flyback goes to a sealed "lump" just
before the anode cap, and the focus wire exits from this "lump" and
goes to the neckboard, where the focus control is situated.
Presumably in this sealed "lump" there is some kind of voltage
dropping circuitry which derives the focus voltage from the HT. I
don't have the manual, but I'm told it mentions a bleed resistor but
gives no value.

The CPC catalogue describes their lead as having a 170M Ohm bleed
resistor.

So, the question is - are these things fairly generic? Will this
replacement lead be OK or should I just go for the full new flyback?

Thanks in advance,

Chad
--
chad.gray@virgin.net
http://freespace.virgin.net/chad.gray/

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[John Bennett]

Re: [ukvac] TECH: Hantarex MTC900 anode cap replacement
In article <8fbdae+7jb9@eGroups.com>, Chad Gray <chad.gray@virgin.net>
writes
>I've got a Hantarex MTC900 monitor which works great when the ambient
>temperature is warm, but when cold the anode cap arcs like crazy. The
>anode cap itself seems to be quite inflexible and doesn't seal well
>when it's cold. I know silicone grease (or "anode cap goo" ) might
>well sort this but I'd prefer to replace the cap with a new one if
>possible.

There's not an awful lot to an anode cap. If your anode area is arcing
excessively when cold (and damp?), then your first plan should be to
unclip the cap and clean the surrounding area thoroughly with a dab of
washing up liquid or cleaning solvent (used carefully) to remove
conductive "goo" from the vicinity. A fresh glob of silicon grease
smeared round the area will prevent the anode terminal from arcing
across the back of the tube to the conductive coating on the outside of
the tube.

If the problem is to do with tracking over the back of the tube, then a
new anode cap won't sort the problem. Neither will smearing more grease
on without cleaning away the old stuff, since the tracking will still
occur underneath.

--
Clive Mitchell

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

 

[Ravage]

Re: [ukvac] TECH: Hantarex MTC900 anode cap replacement
Clive,

Good tips matey... but have you seen a MTC900 anode cap? Its
obviously like a normal cap, but then it has a rim around it...
terrible ascii cart coming up....
_.,-' '-,._
| |

Probably egroups will screw that up, but the second line with the
pipes is the important bit. Tghis is like a 5mm rim around the cap.
Now Chad's (like mine) whole cap has gone brittle and nasty and very
inflexible.

I sill cant believe how this rim is supposed to make good contact
with the tube - stupid deign methinks... Will the magical goo
combined with the pull of the latched clip hold it in place? (Watch
out Chad, if the caps brittle the clip'll be frangible and snap easy -
thats what happened to mine :{ ) My monitor befre the clip broke
sounded like a wind-tunnel! Yikes!

I notice that on the 900/e, 9000 etc they abandoned this bizarre
design (no guesses why ;p).

Anyhow. Anyone got a photocopy or scan of the 900 or 900/e manual - I
See they're not on wiretap - along with WG46xx - monitors. If anyone
has these, pass me a copy and I'll PDF them for the net's benefit ;P

Cheers
Ravmeister

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[Guests]

[ukvac] Re: TECH: Hantarex MTC900 anode cap replacement


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

 

[chadsarcade]

[ukvac] Re: TECH: Hantarex MTC900 anode cap replacement
Hi,

> You cannot replace the lead on the transformer, as it is potted in
at
> the transformer end, and joining the two leads would not be safe...

On the MTC900 the lead is held in place at the LOPT by a screw
grommet - if you unscrew the clip the lead simply pulls out. The
anode cap itself can't be removed as it's moulded into a plastic lump
where the focus wire exits (unlike the "standard" LOPT types the
focus lead does not come directly from the LOPT on the MTC900)

The surrounding area is already spotlessly clean, but as Rav said in
his post, the anode cap itself is a rather daft design as well -
instead of the usual cone shape it's more like a jam jar lid, the lip
of which should make contact with the tube but it has puckered
slightly and doesn't have much give, so doesn't seal very well.

You can see the CPC part I was looking at here:
http://freespace.virgin.net/chad.gray/anode.jpg

Thanks,

Chad

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[Guests]

[ukvac] Re: TECH: Hantarex MTC900 anode cap replacement


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

 

[chadsarcade]

[ukvac] Re: TECH: Hantarex MTC900 anode cap replacement
Hi,

> But I'm a bit unsure about this plastic lump and focus wire
business.
> If it is just a bleed resistor then disconnect the anode cap from
the
> tube and either the EHT from the LOPT or the focus wire from the
> focus control and measure the resistance from the cap to the focus
> wire. If it is around 170M Ohm then use the CPC lead and you should
> be OK.

OK, I'll give that a try

> On the other hand the plastic lump could be an external tripler in
> this case there will also be an earth connection, as well as the
> focus control output. If it is a tripler then it can be easily
> replaced with a universal tripler which will come with a new EHT
lead
> and anode cap.

From memory I think there is an earth connection at the LOPT, the
anode wire looks to be screened and the screen is connected to a
screw on the LOPT. I'm not sure if the focus voltage is generated
from the HT in the "lump" or on the neckboard, the focus adjustment
is on the neckboard itself so it may be done there, in which case the
anode lead may just contain a bleed resistor and I'll be OK with a
CPC replacement...

Replacing the whole flyback seems like overkill but is sounding a
safer bet!

Chad

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