If the back plate is solid metal, it might be a heat sink. I wouldn’t drill into that! Have to open it up to see if that is the case. WHile a flat plate isn’t as good as a finned heat sink, it’s certainly better than no heat sink. Or maybe NCE uses a part good for 10+ amps IF PROPERLY HEATSINKED so with no heat sink it’s still good for 5 or something - though I’d seriously doubt that as the higher current version of a part would typically cost more than the lower current part + the cost of a heat sink.
You’ll get plenty of heat in the SB3 is it’s cranking out 5 amps - the entire current draw of the railroad goes through whatever they use as an output amplifier, so that part will get plenty warm at higher loads.
Finding pictures of the insides of any of the systems is tough, but it looks like the PB-105 and PB-110 boosters also are not ventilated, but the output stage tranistors do have individual heatsinks and they might also be attached to the backplate, allowing the entire metal chassis to be a heat sink. Obviously it works or there’s be a lot of people complaining.
After what some might consider to be a bit of a false start with the first Smart Booster, I have a real hard time that a company of NCE’s reputation would not be very sure that the replacement was going to be just fine? Surely heat dissipation would be a prime consideration of any booster design, so I would be really surprised if the new model needs drastic modification by the owner.
I just went down and looked at the enclosure for the NCE PH-Pro 5 amp command station/booster combination and there are no ventilation slots there, either. I have not heard of any owners of this system complaining that a lack of ventilation has resulted in a failure of the unit. So if NCE can manage to build one of those systems and keep it cool, what would lead me to believe that they could not build the Smart Booster and accomplish the same thing?
The thought had occurred to me that perhaps the metal enclosure panel might be some sort of heat sink. I believe the original SB3 enclosures did need to be modified by adding 1/2" OD holes because of the need for additional heat dissipation. This is how mine came:
When I sent that one into NCE for repair in December '08, they sent back a brand new replacement FREE. The issue was a faulty board which, according to Larry Larson @ NCE, were “problematic”. The replacement came with no additional holes drilled into the enclosure and I never had a problem with it.
I had problems with my 2 sb3’s before switching to the procab. Looks like they fixed the problems with the SB3a and are trying to get the old units off of the street with the discount upgrade. Good move on NCE’s part. Wish I kept my blown SB3’s but they wen’t to the trash dump in the sky. [;)]
The metal back is acting as the heat sink. Those two screws no doubt screw the output amplifier to the metal plate. The metal tab on such parts is often the ground side of the connection, hence a screw in the plate for ground connections. The other hole looks like a mistake or a design change. The drill bit marks above it and the slightly sloppy bottom edge leads me to lean towards ‘mistake’
