Here is some helpful information describing voltage measurements for the RD600 series timers that are often confusing or misunderstood.

I measure 24VAC between VCommon and every valve terminal

This is due to one of these likely issues in order of likelihood:

1. The common wire is not making a good connection somewhere. I’d check the valve box(es) for the common wire and make sure it’s a good clean connection to all the valves.
2. Measurement with the volt meter is being done on the incorrect terminals. You should put one probe on the valve terminal and the other on the VC terminal (I think you did this correctly, but just in case)
3. The system (both timer and terminal board) should be sent in for repair
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I measure 0 V on the 24VAC terminals

This is due to one of these likely issues in order of likelihood:

1. The cold meter is set to measure DC instead of AC.
2. Power is disrupted in some way; ever to the DIY Troubleshooting page item C
3. The transformer has failed: See item D on this page.
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