Stratix III. Problems with JTAG and Fast AS

A nCE pulldown of 10K is according to Altera AS programming circuit examples and supposed to work correctly. But there may be a problem if the line is picking up interfering signals. A small capacitor (e.g. 100 pF) in parallel should also help in this case.

P.S.: Not detecting the JTAG chain indicates severe JTAG hardware problems and usually won't be caused by interfering signals or slightly to high resistor values. It would be a different case, if you notice configuration problems with large images. If the chain discontinuity is a permament problem, you first should check individual JTAG signals with Quartus JTAG debugger and an oscilloscope. However, if all input signals seem OK and TDO simply doesn't response, there may be a more general problem of power-on-reset and device initialisation. But I'm not using Stratix III and don't know about particular issues.