Bachmann HO Scale GP9/7 Fatal DESIGN FLAW
- - - Only Applies If Running On 15" Radius Or Tighter Track - - -
This is NOT an issue on 18" or broader curves. If you’re running a Bachmann HO scale GP9/7 with DCC or DCC/Sound on 15" radius or tighter track, get it off the track right now! There’s an inherent design flaw with this locomotive that will FRY the circuit boards and permanently ruin your locomotive. Yes, we’re talking CATISRPHOIC FALURE!
Recently, our engineers fielded a number of complaints that appear to be symptoms of a burned out motor. After weeks of testing, we finally determined it has nothing to do with the motor. In fact, with units that suddenly stopped running or slowly needed more power until they stopped running, we completely removed the motors from the chassis and they all tested fine. The problem we found is as old as the hobby itself.
Bachmann’s thirst for low cost locomotive assembly methods backfired on this locomotive. Bachmann failed to properly insulate the motor body from the negatively grounded chassis. Anyone familiar with DCC systems will tell you the sure fire, fastest way to turn a perfectly fine running locomotive into junk is a split second short across the metal motor housing and the chassis. All this could have been avoided, but it would have added the cost of some Kapton tape and a few precious assembly seconds for each locomotive.
At first glance, the motor appears to be perfectly centered in the chassis, on its seemingly well engineered plastic motor mounts with a gap between the chassis and the metal motor housing that you could easily fit a piece of paper in between. Now, we all know motors spin. And, in HO scale locomotives, they spin pretty hard while the drive shafts push back against the motor as the trucks swivel, especially on tight curves. The idea was that if Bachmann engineered the motor mount to such high tolerance, there was no way the motor could ever touch the chassis. To do this, they engineered a tiny flange ridge on the plastic motor mount. Properly installed, this ridge abuts the cut metal edge of the motor housing. You can see where this is going.
The slight plastic bump ridge is no match for the spinning motor forces inside the tight fitting shell body of the locomotive. Eventually, the motor rotates just enough in its mount to repeatedly discharge a short across the DCC system through the metal motor housing contact with the negatively charged chassis. A more devious person might think this is a clever method of planned obsolescence, whereby you buy a low cost, low level Bachmann locomotive with DCC or DCC/Sound at a bargain price that quits on you within a few months so Bachmann can sell you another. Given that motor shorts as a cause for DCC system burnouts goes back to the beginning of time in the hobby, it’s tempting to think this may be true. It’s not like Bachmann has ever had a history of being deliberately devious, right?
Anyway, here’s the easy fix. Take the locomotive apart all the way down to the separated motor & chassis. Cover the metal motor housing with Kapton tape, paying particular attention to the sharp notched end of the motor that fits into the chassis body. Use just enough Kapton tape to cover the metal with a single layer. Too much, and the motor will not fit into the chassis, too little and poof goes your DCC system. Simple, right?
Well not really, unless you’ve taken hundreds of locomotives apart and put them back together like we have. The right way. So, they run well, again. It does takes some time, planning and a well-organized workbench. If you are careful, and keep track of where everything goes while you are disassembling the locomotive, you should be able to do it.
Don’t rush. Give yourself plenty of time. Tapping a few brain cells during disassembly will make reassembly easier. You will also need a complete set of small jewelers straight and Phillips screwdrivers. A hemostat - the tiny locking Pliers surgeons’ use – available at almost any hardware store now - is extremely helpful in reassembly. You’ll also want to have your best, narrow tip, low wattage, 25 watt or less, soldering iron on hand. You will find at least one cold soldering joint and/or break a micro wire off in the process. In a few hours, when you’re all done, you will have the reliable locomotive Bachmann should have built right for you in the first place. I’m sure the Bach-Man would love to hear how well it goes for you. Be gentile.