SDG #119 Building the DC-DC PCB for the FY6900 Signal Generator

The FY6900 is a capable, low cost arbitrary waveform generator, but its stock internal linear supply ties it to mains power and adds bulk. This build documents a custom DC-DC converter board designed to replace that arrangement, letting the generator run from a single DC input while still producing the split rails the analogue output stage needs.

The interesting engineering problem here is not simply generating the voltages, it is doing so without wrecking the instrument’s output quality. Switching converters inject high frequency ripple and common mode noise, and a signal generator is exactly the sort of device where that shows up immediately on a scope trace. Component selection, layout, ground return paths and output filtering all matter far more than they would on a general purpose power board, which is why the design deserves a full assembly and verification pass rather than a quick bench hack.

Assembly covers reflow and hand soldering of the SMD parts, checking for shorts before applying power, and bringing the board up carefully to confirm each rail lands where it should under load. Measurement work then uses a differential probe to look at ripple and switching artefacts properly, since single ended probing on a floating supply is a good way to fool yourself.

For anyone considering a similar modification, the takeaway is that a DC-DC swap on test gear is realistic but needs verification with real measurements. If the generator’s noise floor and output cleanliness are unchanged, the modification is a genuine win in portability and thermal behaviour. If not, the linear supply was earning its keep.