Re: Relocating/replacing capacitors and filing edge of board on Titan-SD


kelly dorf
 

HI Ben,
I posed your question to one of our engineers, and I got this lengthy answer:

And this is where my questions come in: first, would it be possible to replace these capacitors with smaller ones of the same specifications, or replace them altogether with a single keep alive? Second, is there any reason I shouldn't file the edge of the circuit board back about 1.5mm as long as I don't remove the through holes for the capacitor? It is always risky to file on ECB's. The filing itself can create static charge (especially with a Dremel tool), that can damage components and there is a risk of shorting or damaging buried wiring runs in the ECB. I did review the check-plots for the 050-0172-01 circuit board and there are no ECB runs from the capacitor's through-holes to the end of the board except for the ground plane and the 5 volt supply plane; there is always a chance that these two place will short together from the filing but a visual inspection of the board edge after filing should revile any problems. Replacing the capacitors with equivalent one's is acceptable but when this system was designed, we used the smallest ones we could get for the total capacitance necessary. Of course, technology keeps improving so it might be possible to find physically smaller ones at the same capacitance and voltage rating. I'm not sure about the keep alive working on the SD boards but in principle it should work. I know some boards have internal circuitry, but I'm not sure about this one. And last, what is the purpose of this metal piece that is screwed in on top of the decoder, as it does not appear to be contacting anything electrically: The Titan FX SD board runs hot because the ECB design used a linear voltage regulator to reduce sound system cost for the locomotive manufacturer. The metal plate acts as a heat sink that transfers the heat from the linear regulator mounted on the ECB to the ECB mounting screw to the metal support and down to the chassis. 

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