Can anyone help? Run out of ideas of whats wrong

Suz, three things spring to mind.
Voltage - being DCC which is a form of AC, it needs to be read with an AC voltmeter & while a standard digital meter will not be accurate, it should read around 13v.
second point is loco wheel & track cleanlines, dirty wheels & track are more of a problem with DCC than DC - clean them with electrcial contact cleaner or Isopryol alcohol or something similar. Track at points needs to be clean especially if using the point blades to feed power - where they contact the rail, they have to be spotless.
third point - wiring - loose metal fishplate/railjoiners will give problems, suggest that a loop of wire is soldered across the fishplates.

I would suggest that if this is your first attempt at DCC, obtain the book - Aspects of Modelling - Digital Command Control by Ian Morton - should be readily available via the Internet if no local shop has it.
Can you indicate what type of DCC system you are using?

Suz X

I would recommend that you address the problem in two stages.
As Sol has suggested, check out the wheels of the locos as they need to be clean and also check the pickups that sit behind the wheels where they should be making contact with the wheel rims - they can be become lose and or dirty.
Once you have the locos traveling OK on the normal track - then focus on the points

Points are always problematic especially with small trains - large trains should run more smoothly since in theory they have more pick ups which can be spaced further apart so that have only one set of pick up wheels on the point at any time (If the DMU is stalling it may be because it is only be picking up from one set of wheels which would be about the same distance apart as the smaller locos).
Here are a few suggestions that may help.
- Does the train stall irrespective of the direction of travel?
- Does the train stall irrespective of which way the points are set?
If the answer is yes to both then dirty wheels/pickups on the loco are the likely suspect
If your answer is no to either then the points are most likely culprit

If you are able to watch the locos at eye level as they pass over the points, first ensure that all wheels are touching the track when it stalls - see if you can identify if it is the same spot every time - without touching the loco gently push the black/brown plastic that is used to change the direction of the points such that you are trying to push the points further - i.e not change them. If the loco moves again then your problem is most likely dirt between the fixed track and the switching blade ( the track that moves).

Hopefully this all makes some sense and is of some assistance.

Dave

Suz, the advice so far is OK and wheels are the likely culprit followed by the need for more power feeds around the layout. If its an 8x4 board or similar, then 4 feeds per loop should be enough.

A second problem may be pickups. Unfortunately the construction quality can be a bit off so pickups don't really touch the backs of the wheels very well. If you look closely under the loco, you will be able to see some fine "fingers" that touch the wheels one side. Make sure they do touch the wheels well and bend a little towardsthe wheel with some tweezers if they don't make firm contact. Also check that the wheels are very clean where they are supposed to touch as they have a tendency to pick up fluff and muck.

Even if they LOOK clean give them a good rub to remove invisible oxides and muck. Careful use of some acetone based fingernail remover or similar on the wheel backs (just a damp cotton bud) to clean them will help too. Keep this away from any plastic though of course.

The other problem will likely be the hornby points - they are very fickle as to reliability of contact between blades and the rest of the rails so really do need a little TLC to keep working. In future, consider buying Peco points which are a tad better.

Perhaps you could experiment and work by elimination: make a largish loop of track only with no points - test. Add a couple of points - test. change to two more points - test. This way you just may find the intermittent ones and can then replace or improve them.

Kindest regards

Richard

QUOTE (Sol @ 28 Dec 2008, 06:56) <{POST_SNAPBACK}>Voltage - being DCC which is a form of AC, it needs to be read with an AC voltmeter & while a standard digital meter will not be accurate, it should read around 13v.

Sol: An AC meter can be a LOT out, rarely just a little. Basically the ONLY way to get reliably within one volt is to measure the DC voltage across a function such as blue and white (with F0 turned on). A standard meter set to AC will be up to 50% out as the phasing error is related to the Waveform relativity betweeen meter (50/60 hz and the track power (in the thousands of cycles).

If a meter is to be used, totally ignore the voltage reading and use it to see change around the layout - its error will be constant so variance will be seen the same as if it read correctly.

Richard