What are the functional and other diiferences between the UP3 and UP5 panels. Are they completely interchangeable?
The only real difference is the UP5 has the ‘side jack’ for an extra connection for downstream devices that do not need the railsync signal. So, a throttle would work there, or a DS64, but a booster or a BDL168 would not.
–Randy
I have both on my layout. UP5’s replaced UP3’s years ago. Other then the extra side jack on UP5 there is no functional difference between the two. Both are just places to plug throttles, etc. in.
On the actual UP5 circuit board there is an extra resistor to help protect the steering diodes. The resistor can be added to a UP3 for a few cents and a couple of minutes work. Personally, I just left my UP3’s as is because the diodes can be repaired just as easily if damaged. No damage after about 15 years of use.
Martin Myers
Thanks Martin and Randy.
“Steering” resistors? Meaning?
Steering DIODES. There are 3 power sources to feed the throttles plugged in to the front of the UP. One is the Railsync linesof the Loconet cable plugged intot he back, a second is track power connected tot he two screw terminals on the back, and the third is the 2.1mm jack on the side where you can plug in a power supply.
Since diodes only conduct in oen direction, it’s an old trick, each power source feeds through a diode. That way, if one has a higher voltage thant he other, it can’t feed back and cause damage, the diodes won’t allow the power to flow. It’s possible but rare that a momentary short when plugging a throttle in could cause too much current to flow in a diode and burn it out, that’s why the UP5 added a current limiting resistor to the mix, even under a dead short the current is held to a level the diodes can withstand. I only have UP5’s since all my Digitrax equipment was purchased after the UP5 came out, but I’d trust Martin on this that the chances of actually causing the UP3 to fail in this manner is rather remote. I keep looking at UP3’s but since they are perfectly fine to use, even used ones on eBay go for as much as a new UP5.
–Randy
Is there a simple way to checkout diodes on a UP5? We have one that appears to prevent shutdown of our DCS200/PM42’s when supplied with 12 v from a wallwart, no shutdown problem when 12 v disconnected.
It’s rare for diode to fail in a shorted state, but that would be the only way 12V power fromt eh pwoer jack could get on the Railsync of the rear jacks going to the command station. Even most cheap meters have a didoe test function (I know the $5 Harbor Freight ones do), so you could just test each diode (with everything disconnected of course). You could also plug in the power suppyl and nothign else, no Loconet cables, no throttles, and measure the voltage on the outermost pins of the jacks on the back. You should see no voltage there if the UP5 is fine. If you check the front jacks, with the power supply connected, you shoudl see the 12 volts less about 1 diode drop on the outer pins. ANother way might be with a DT throttle, when first plugged in they show the voltage. Use one without batteries. WIth the 12V connected but nothing else to the UP, plugging the throttle int he front should show 11 volts or so briefly before it goes dead for lack of Loconet. Plugging it int he rear jacks should do nothing, because there should be no power there.
Oh and super sanity check - make sure the UP5 was not put together backwards. The FRONT side is the one with the LED in the middle. If you plug the Loconet in here and try plugging throttles int he other side, you’d have all sorts of problems, including 12V always on the Railsync lines going ot the command station.
–Randy