No you cannot get into those ballasts. Its a nasty trick so you have to
replace them.
Now I'm intrigued. Are the tubes merely in series with only one set of
heaters active? I saw a system like this, it was a bodge and I never did
understand how on earth it ever worked as the voltage had to break down two
tubes not just one. If you try this sort of thing with neon's you either get
nothing or a kind of brightness oscillation effect which is not really what
was wonted.
I also remember some old Woolworhs strips with two tubes and they end
plugged into a bayonet. There was no choke and just a small little
encapsulated blob. It worked but not when the weather was cold!
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Roger Mills" wrote in message
...
On 23/11/2018 22:43, Roger Mills wrote:
I have an illuminated bathroom mirror which has two unsilvered vertical
strips with 15w T8 fluorescent tubes behind them. The tubes are powered
via a single 2-way electronic ballast.

The lights have suddenly developed a fault. When turned on, they light
normally but then go out after a few (4 or 5) seconds. If I then turn
them off and wait a minute or so, I can turn them on again - and the
cycle repeats. There's no way they'll stay on more than a few seconds.

Anyone come across this sort of thing? AIUI, the ballast is supposed to
deliver a high start-up current and then cut it to a lower level for
running. So could it be cutting the current to zero rather than to the
proper value?

Is replacing the ballast likely to fix the problem, or could the tubes
be at fault?

The ballast is a Kengo KEB-215. I can't find one of these anywhere, or
even one of another make with the same spec. The nearest I can find is a
Tridonic 22185216 - which is 2 x 18w rather than 2 x 15w. It's also
slightly longer, so I'd have to bodge the mounting brackets. Assuming I
can make it physically fit, is the difference in electrical spec likely
to be a problem?

Many thanks for the all the comments.

I think it was probably a bad connection on one of the tubes. I took both
tubes out and turned them the other way up - and it started working ok.

For future reference, can you get LED tubes which fit the same sockets? If
so, do you junk the ballast and just connect them directly to the mains?

With regards to checking the ballast for failed caps, etc. - the whole
thing seems to be pretty much encapsulated, with a few wires emerging from
both ends. I doubt whether it could be opened up non-destructively.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.