Power Cab – Radio Upgrade, thanks to Mark Schutzer.

These basis of these notes and the modification photo are courtesy of Mark Schutzer who understands electronics much better than me, who has designed a Radio Repeater system and an on board charger for the Procab, Select NCE Articles, did the modifications first and passed on the instructions to me. Now thanks to Mark, I have a Radio Power Cab – Thanks Mark.

NOTE: Doing this modification will certainly void your Power Cab warranty.

This modification will require removing and installing some small Surface Mount transistors and FETs, so a small soldering iron and a very steady hand will be required. As the Radio Upgrade Kits are no longer available as a separate item from your dealer, you will have to use one of your radio throttles Radio board and parts to do this. These notes are for those NCE users. Others will have to return your units to NCE for the Radio Upgrade. This is the procedure for all throttles now.

When I bought my Power Cab in Aug 05, I asked NCE if the Power Cab supported radio operation as I wanted to add one of my Radio Upgrade kits from a Cab04P and they said yes.

To check this out, I just swapped my newest Procab’s rear housing that had the Radio board and the battery compartment with bits and wiring complete. I wanted to check it out first, that would save time if it did not work.

I tried the Power Cab plugged in and then removed the coily cord. I tried to turn on the Power Cab and it only showed a display as long as the “EMERGENCY STOP” was pushed. I tried the ON/OFF switch modification from NCE Files and this now had the display on all the time but not at the “Operating Display” (I think – Alzheimer's kicking in already). Removed the ON/OFF mod and was resigned to the fact that radio did not work. I mentioned this to Mark and just got used to the Power Cab as a plugged in Procab.

Recent (December 06) Power Cab discussion on the NCE Yahoo group, a member suggested he was returning his Power Cabs to NCE for the installation of the Radio Upgrade kit. Mark replied that I had tried it and it did not work. I posted what I had done and my above results. Tim from Empire Northern Models suggested it was possible and he had done some.

I emailed Mark and he tried to upgrade his Power Cab and got the same results as me. Mark again emailed me again with a “solution” that solved the puzzle. Below are the instruction and photos.

Adding the Radio Upgrade Kit, some Power Cabs work and some don’t (Mark’s and mine).

The problem with the Power Cab is that there is +3 volts on the +12 volt line when it's running off the radio and not even plugged into the cab bus. The +3 volts is enough to fool the radio module into turning off.

The reason some of them work is that there is a resistive voltage divider on the radio module that divides the +3 volts down to +1.5 volts. On some radio modules, this 1.5 volts is seen as a high logic level turning off the radio. On other cabs it's seen as a low logic level and the radio stays on. The bottom line is that it is right on the edge and can go either way, that's why some work, and some don't.

The best way to rectify this problem is to replace the Power Cab’s Q4 and Q8 transistors with FETs, that are located at the highlighted positions on the Power Cab’s circuit board as shown below.

Replacing transistors Q4 and Q8 with N channel JFETs (2N7002) is easy, as they drop right in on the same footprint on the Power Cab’s circuit board. After swapping in the FETs, the +12 volt line read +0.3 volts, plenty low enough for the radio to stay on.

The 2N7002 FETs are used on most NCE HO decoders to drive the function outputs, like the DA-SR, D13SRJs etc. As you only need two of these 2N7002s, a convenient source is an old, possibly blown up NCE decoder that you haven’t thrown out, or you did throw it out last week, or one that you are not using any of the function outputs like the “lights”. You can steal the FETs from the decoder. The 2N7002s will be marked with “72” on the package. Mark said there are 5 of these FETs on a DA-SR decoder. On my D13SRJ there are 8 of these FETs (3 legged small black rectangular “blobs”) and had “72UOA” written on them but on the early D13SR version 3.2 had FETs with “72sKC” on them.

These FETs are also available from stock at www.digikey.com under the part number 2N7002LT1 and cost $1.87 US for a quantity of 10 pieces. I'm sure you can also get them at any number of places online under the generic part number 2N7002. In Australia the 2N7002LTIs are available from Farnell In One Chester Hill, Sydney at 74 cents each.

Swapping out the transistors with FETs, you can plug in the radio module and it will power up correctly - right on!

To remove the Surface Mount FETs and transistors, hold them with a pair of tweezers and heat up the “single” leg and it will release and twist up. Then heat up the two “other” legs and you have got it, if it has not flipped out onto the carpeted floor. Will never find them, then. In each case not too much heat or “time”.

My removed FETs work great in my Power Cab.

Happy de-soldering and be careful.

Thanks Mark.