This is a replacement for the A21 Voltage Controlled Oscillator board mounted to the acquisition board in Tektronix TDS500 series oscilloscopes. (It may be used in other scopes such as the TDS600 series, but I haven't checked).

Parts substitutions are allowed, but just be sure to use C0G/NP0 capacitors and low temperature coefficient resistors (I suggest 50ppm or lower) for stability.

The CR101, MMBV105G is an obsolete part, so reuse it from the old board. It is far away from the electrolytic capacitors (which have leaked, hence the replacement PCB) so it should be fine to reuse.

If you find a suitable substitution, feel free to use it and let me know so I can update the build files.

A recalibration of the scope may be required (I suggest it if you can) but it is an arduous process to do, so just run with it as-is and see how you go.

[EDIT]

I performed a full performance test on the oscilloscope and it passed all tests with flying colours.

At least in my case no recalibration was needed at all. All results were much better than rated limits.

[UPDATE]

I've cleaned up the footprints a little for ease of manufacturing, and added a Pick and Place file too.

I have now fitted these boards to a number of scopes and they all work great.

I am still looking for a replacement for the MMBV105G, so if anyone has a suggestion, please let me know!