On Tue, 20 Dec 2011 17:20:01 -0500, "Robert Green"
wrote:

"Jennifer Murphy" wrote in message
.. .

My multimeter arrived today. I cannot get to the wiring underneath the
dollhouse because there is paint and glue drying. ;-)

Welcome to the wonderful world of electrical troubleshooting. I have about
20 meters (maybe 30) because they are indispensable for electronics work.
Some hook to PC's for recording work, some are small and lighted that I keep
in my car. I keep one in my camera bag, one connected to the battery
powered sump pump and even have a AA-A battery charger that reads the
voltage of each cell as it charges. My wife says it's a sickness but I
believe you can never have enough multimeters, flashlights or rechargeable
batteries. (-:

I tried to get a voltage reading at the light sockets inside the doll
house. I could not get a consistent reading. The space is very cramped
and the sockets very small (3/8").

For testing like that I might make up a test prod from a dowel about the
size of the bulb with a screw in the center to simulate a bulb, but that's
probably a bit much for you just starting out.

I don't have the tools for that ;-(

It takes a delicate hand to
read a micro-socket when it's on a test bench. Mounted in a doll house
might be much harder and close to impossible without the right probes. One
the backside of the socket there are often screw terminals. That would be a
good place to check the socket voltage.

I can't get to the back side. The sockets are mounted in the ceiling. On
the first floor, it's about 1/2" thick and completely finished. On the
second floor, there is an attic, but it's sealed. I don't want to start
taking it apart.

I seemed to get a better reading on
DC than AC. The DC readings jumped all over the place, but it looked
like between 0.9 and 1.1 v. The AC readings jumped around even more. The
most consistent reading was 6v at one socket.

Is there a way using this meter to tell if the current is AC or DC?

That's a good question. Measuring an AC voltage using a high quality,
accurate voltmeter, that set to measure DC volts, should, by definition
result in a reading of zero volts. The reason you read a small residual DC
voltage when measuring an AC voltage might be because of small inaccuracies
in your meter. Any true AC voltage has absolutely no DC component. I would
test it using a diode - even an LED would work - that will pass current in
only one direction. But that's little advanced. I suppose you could test
the circuit by reversing the probes. If it's DC, the + and - signs should
reverse themselves when you switch the probes. With AC, it shouldn't have
any effect.

I thought I got a +/- change one time, but it's so difficult to get at
the sockets, that I can;t be sure I'm getting good contact and not
shorting the probes.

Next, I did a continuity test of the bulbs themselves. Of the 12 bulbs I
removed from the house, only one passed the continuity test.

Excellent work! With an old dollhouse and the possibility that the bulbs
are getting more voltage than designed for, it's very likely the only
problem is burned out lightbulbs.

I ordered a bunch of 2.5v #14 bulbs. They should be here tomorrow.

I then tried a resistance test on the bulbs. The one that passed the
continuity test showed 11 ohms of resistence. The rest showed infinite
resistance.

That sounds right. Infinite resistance means the filament is broken and the
bulb is dead. You should be able to confirm that with a magnifying glass.
If they were run at double their rating, the filament damage should be very
obvious and might include blackening of the bulb's interior.

The filaments all look OK. A couple are somewhat blackened.

I then took the good bulb and tried it in several sockets. After
fiddling with the button switches, I was able to get it to light in
several sockets. It was very dim.

You may also be experiencing problems with dirty switch contacts and dirty
or corroded bulb sockets. The center button connector of the socket should
be nice and shiny in each socket. I bet they're not.

The switches are definitely at least a little suspect. They are the
push-button type. They are a little loose in the housing and if I jiggle
them, the lights flicker. I can't see into the sockets, but the house
has been stored in garages on the east coast (humid) for many years. I
might go get a mirror on a stick and see if I can see into the sockets.
But if they are corroded, there ma not be much I ca do without taking
the while thing apart, which is too much for this Christmas.

When everything dries, I will try to get under the house and see if I
can get better readings.

I don't think you have to do a complete rewire - if it were 110VAC passing
through those wires you would have seen the bulb go supernova and possibly
pop. There's got to be a transformer somewhere.

Yes, I'm quite certain that it's not 110 and probably not AC.

By getting the bulb to
light in several sockets you've conclusively proved they can not be wired in
series (in a chain like old Christmas lights where if one bulb went dead,
they all died). That's important to know.

Yep, I was glad to discover that.

Trace where the AC wires comes into the dollhouse and find the transformer
(apologies if you've already done this - I just started reading this
thread.). If it's well wired to the cord and the cord's in good shape, I
wouldn't rewire the unit. Switches can often be "decrudded" by operating
them a few dozen times to scrape off the oxidation.

The AC cord is one of those really old fabric-covered types. The place
where it goes into the base of the house is just a hole in the wood with
no fitting or stress relief. There is no obvious wear that I can see,
but it all seems a little unsafe to me.

I think the next step is to clean the sockets, cycle the switches, install
the replacement bulbs and take it from there.

I managed to get under the house. The whole bottom is covered and glued
shut. I'm starting to think that this wasn't that well made. I'm tempted
to cut the cord and go without lights for now. If the little girl really
gets into it (right now she's more into Buzz Lightyear), I'll consider
taking it apart and installing LEDs and a battery pack.

Anyway, thanks for the thoughtful and patient help.