I bought an inexpensive Timex HRM 3 or 4 years ago. It's worked fine up until this year. When I started riding again a couple of weeks ago I noticed that the readings were intermittent, in that some of the time they seemed right, but other times they seemed to be about 1/2 of what I would expect.

I replaced the batteries in both the chest band and in the wrist watch unit.

Now I can't seem to get the HRM part to work at all. I press the button to cause it to try to read from the HRM, it shows three dashes, then just goes back to the time display.

(I no longer have the manual for it.)

Any ideas?