A poster on another forum had the exact same problem that I am having (with the same equipment) and summarized it better than I could, so I will just paste her summary below. Unfortunately, she never received a solution to the problem (by the way I have this problem with the serial connection and IR blaster connection. I have tried both separately.):
My Series 2 TIVO suddenly started experiencing the same channel changing problems the others described. One moment it was working fine, and then suddenly it's been unable to correctly change channels when recording programs. It was no gradual change either; it just suddenly started having problems.
I have a Motorola box, connected via serial port to TIVO for the channel changing. (I have tried IR in the past, but have had VERY poor success with channel changing using this method - especially for the 3-digit channels - so I don't consider this a viable option that would "improve" or "fix" the problem.) What I am noticing is that if the cable box needs to change from a higher number to a lower number, TIVO first changes the channel to the correct number, then almost immediately goes down 1 more number. Vice versa for the other direction - the channel ends up changing to a number that is 1 higher. However, if the cable box is already positioned at the correct channel (and I have used the cable box remote to do this, so TIVO does not know that the channel has been changed), TIVO leaves it there and records the correct channel. I can understand this last bit if TIVO had just been recording on that same channel, but not when I've used the cable box remote (unknown to TIVO) to change it. Seems like TIVO would still try to change the channel (I dunno... maybe it does, but the cable box knows it's already where it's supposed to be and ignores the signal to change channels???)
Occasionally, TIVO will record the correct channel, but it's really hit or miss. For example, out of a block of 6 programs on 6 different channels, sometimes (actually, most of the time) I might get only 1 channel changed correctly, and "garbage" (wrong channels) for the other 5. But other times, I might get 4 or 5 channels changing correctly. And it doesn't seem to matter whether the channels are single digit, double digit, or triple digit. (I know with IR I really had trouble with the triple digit channels). But more often than not, I am noticing that the channel changes are usually NOT working correctly for most, if not all, of my programs. Getting 4 or 5 out of 6 correct temporarily lulls me into thinking it's "working" better, but unfortunately that doesn't seem to last for long.
I have tried the following "fixes", but with little or no success:
1. Turned off the power button on the Motorola cable box and then powered back on.
2. Physically unplugged the cable box from the power outlet, then plugged back in.
3. Restarted TIVO from the menus.
4. Physically unplugged TIVO from the power outlet, then plugged back in.
5. Disconnected the physical serial cable from both the TIVO and from the cable box, then reconnected them again. (The only thing I did NOT do was replace the physical serial cable with another).
6. As a last resort, ran Guided Setup again on TIVO.
The only discernable improvement with any of these "fixes" is that usually the channel changing was not quite as severe... for a short time (i.e., less than 1 day), that is - then it went back to having problems with nearly every channel change.
I am assuming that the problem lies with the TIVO because when I use the cable box remote (had to dig that one up, since I normally only use the TIVO remote) to directly change channels, there is no problem whatsoever. But when I use the TIVO remote - which means the signal is first going through TIVO - the channels do not change correctly; they go 1 more up or down. This goes for entering the channel number in via the numeric keys or using the up/down channel buttons.
Is this problem then a symptom of other problems with my TIVO? Or should I try totally replacing the physical serial port cable? Could the serial port on the cable box (or TIVO) suddenly "go bad"? Or do I switch to IR channel changing... (but only if there's a way to make the IR option work better)? As it is now, my TIVO is virtually worthless for making recordings (which is what I rely the most on it to do, as I rarely watch live TV). Any help or ideas (beyond getting a new TIVO - which I can't afford right now) would most be appreciated.