The Ping))) sensor uses a crystal for timing.
Some of the cheap knock-offs actually use a MAX3232 chip (which is an RS232 serial port/usart) to detect the return pulse, just for the carrier detection. If the parallax is similar, these have a fairly wide range of frequencies they work at, since you never know the baud rate to expect, from 9600 up to 1mhz, although they are deliberately not very fussy about accidentally picking up nearby frequencies.
Since there's probably some other logic on the other chips, and everything is probably run off the one crystal, I'd recommend going to lower frequencies, otherwise you're overclocking.
Also, make sure to send a longer trigger pulse because all the logic will be slower.
From the picture, it looks like a 16MHz crystal, which must be divided down to the 40KHz.
So solder in a 14MHz, and an 11MHz, lengthen the 5 uS trigger pulse accordingly, and you should be good to go.
As an aside, you might also consider scanning further apart. If it's taking you 30 seconds, you're probably checking every degree; maybe try every 15 or 30 degrees (just make sure to give the servo time to move)