# inaccurate clock



## Curtis (Dec 2, 2003)

I've noticed lately that the clock is off by more than a minute. It was off last week by almost two minutes. I did a system reset and that fixed it for a couple of days. It seems like the problem started with the switch to daylight savings time.


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## rbtravis (Aug 9, 2005)

You failed to tell us what model Directv Tivo you have? When was the last time you changed the battery (2032). The time displayed on the screen is a display sent by satellite. 
How do you set your watch? Do you use the NIST time standard? I use analogx's program and my computer (NIST) and Directv's time match.


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## Curtis (Dec 2, 2003)

rbtravis said:


> You failed to tell us what model Directv Tivo you have? When was the last time you changed the battery (2032). The time displayed on the screen is a display sent by satellite.
> How do you set your watch? Do you use the NIST time standard? I use analogx's program and my computer (NIST) and Directv's time match.


I have a Hughes DVR 80. I have never changed the battery.

I don't refer to my watch for the exact time although it's always correct within 10 seconds. I look at one of my weather stations that receives WWV time signals.


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## rbtravis (Aug 9, 2005)

The Satellite updates the clock on the main board. The clock from National Institute Standards Time updates both Directv & WWV time. I do not know how often during the day Directv updates its onboard clocks (I believe at least every half hour). That clock is maintained by the 2032 battery. Have you changed it lately?


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## Curtis (Dec 2, 2003)

I have never changed the battery. If it's not soldered in place I might give it a shot. I have a soldering gun but I'm wary of soldering something as heat sensitive as a battery.


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## rbtravis (Aug 9, 2005)

Its in a socket.


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## Curtis (Dec 2, 2003)

I don't know if it's the battery. The clock recalibrated itself on the hour. Seven minutes later I noticed it was exactly one minute slow. The tivo clock switched from 08:06:59 to o8:07:00 just as my WWV clock switched to 08:08:00. Thirty minutes later, there has been no further slowing. I think it's a software glitch.


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## rbtravis (Aug 9, 2005)

Battery is less than $3.00 at Walmart, it won't hurt to change the battery because it is socketed.


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## Phantom Gremlin (Jun 20, 2002)

A number of years ago there was *lots* of complaining about inaccurate time. If memory serves, the general cause was laziness on the part of DirecTV. Also it depended on what channels you were tuned to. E.g. people reported inaccurate time when tuned to locals, but good time when tuned to national channels like CNBC.

Inaccurate time still sometimes happens to my DirecTivos but it's just something I've learned to live with.

I doubt that the battery has anything to do with it. The box is continuously powered except during a blackout. Why does the box need to consult an on-board RTC if DirecTV is constantly sending the correct time in the bitstream?


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## JimSpence (Sep 19, 2001)

The problem in the past was that the TPs on the satellites weren't synchronized to the same time. This caused the onboard clock to update to inaccurate times. We could watch this happen by turning on the onscreen clock. DirecTV did fix this problem, but maybe it has returned. It is possible that the clock chip can lose time until the unit updates from the satellite. 

BTW, the battery on the mainboard is there to maintain the clock and other settings when the unit is unplugged.


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## Richard R1 (Sep 20, 2002)

I think we can exclude the battery as a source of this problem. I have this problem with all three of my DirecTV's, one Philips, one Sony, and one Hughes. Each scheduled show starts recording approximately one minute late. I timed it on my Hughes, and the TIVO time is slow by 1 1/2 minutes.

That's the reason I came here tonight, to see what other people are doing to fix the problem. I am surprised there has been so little commentary on this problem, since it has been going on for some time. I would agree with the earlier comment that it started about the time we switched to DST, which was about two weeks ago.

Do we just wait until Directv does something about it?

Edit: Doing a manual phone-in as well as a restart of the unit did not have any effect on the incorrect time.


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## rbtravis (Aug 9, 2005)

I am having no problems on my machines, but then contrary to popular views in this forum, I have replaced the Eveready 2032 batteries in my Directv Tivo's. I wonder if that is the reason.  Does your electric watch keep perfect time with out changing the batteries?


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## Trent Bates (Dec 17, 2001)

That logic doesn't work in this situation at all.
A watch with a single source of power will of course lose time with a spent battery because it's the primary/single power source.

The DirecTiVo clock is powered by the mainboard whenever the AC is coming in. This is true with nearly every piece of equipment that has both a external source of power and a backup battery.

A much better experiment would be for you (as a person claiming not to have any problems because you've changed the batteries) to remove one of your "replaced batteries" with the unit plugged in and see if the time drifts over a short period of time due to that action.

If you can replicate the problem by removing the battery, then you have most likely found the cause. Replicating the problem is one of the best methods of troubleshooting.

If the units were actually designed in such a way that the battery was crucial in an AC powered situation, it would be a first (and a terrible design) as far as I'm aware.
I've run similar equipment intentionally without batteries and never has it caused time inaccuracies while powered by AC. (The 60Hz waveform of AC makes a really good time reference BTW.)

Having said that, the 2032 cells don't last forever. If the units have spent a lot of time (months to years) unplugged, the cells could be dead and they are only $3.50 to $4.00 in many stores.

For the record, other than the July 14th glitch a couple of days ago that only affected one of my units, I don't seem to have any problems. Two of my units have been in use since 2001 and the other since 2002. None of the batteries have ever been changed. (Furthermore, If I were to get one of my units out of the cabinet and test it, I wouldn't expect it's voltage to be lower than 2.95V.)

This is most likely a problem with the time signal on certain transponders being off. We in the Denver Metro area may not be using (or able to use) the transponders that others are having a problem with. To jump to the 2032 battery as the potential cause is really quite a leap.


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## rbtravis (Aug 9, 2005)

Do you have a schematic of the Tivo motherboard? If so please share it. Tivo is set to run off satellite time and as such only has to be accurate on the half hour which it is when it is reset by satellite. It is a clock chip and computer clocks do not run without power. Also the clock chip is not usually connected to the power supply due to different voltages. With the setup taking time signals from the satellite the time only needs to be accurate on the half hour. With no battery the clock will lose time. The clock chip does store the date also.


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## Curtis (Dec 2, 2003)

JimSpence said:


> The problem in the past was that the TPs on the satellites weren't synchronized to the same time. This caused the onboard clock to update to inaccurate times. We could watch this happen by turning on the onscreen clock. DirecTV did fix this problem, but maybe it has returned. It is possible that the clock chip can lose time until the unit updates from the satellite.
> 
> BTW, the battery on the mainboard is there to maintain the clock and other settings when the unit is unplugged.


Yep. I've come across another local DirecTiVo user that is having the same problem. If I switch both tuners to local channels, the clock jumps to one minute slow within a few minutes of switching channels.


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## Trent Bates (Dec 17, 2001)

rbtravis said:


> Do you have a schematic of the Tivo motherboard?


Yes. I've attached the section of it relating to the RTC circuit. (This is a very simple RTC circuit BTW.)



> Tivo is set to run off satellite time and as such only has to be accurate on the half hour which it is when it is reset by satellite.


It sets the time much more frequently than that. Where did you hear otherwise? I think you are making that up because you think it sounds good.

Back in 1997-2000 I knew roughly what DirecTV was sending in it's data stream. The data stream has changed a lot since then, but I remember time "packets" being sent multiple times a minute. Time data is tiny compared to audio/video.

I'd expect that the time is adjusted after an average sample of consistent time data is received. The clock isn't changed with each time "packet" that is received. Data corruption/loss would wreak havoc on such a system! It's adjusted when a set number of time "packets" agree in series.



> Also the clock chip is not usually connected to the power supply due to different voltages.


And they have no way of providing different voltages to various components? Really???
Every RTC circuit IS connected to the power supply for these purposes. Do you really think that your digital alarm clock couldn't keep time at all if you didn't have the backup battery in there?
The attached schematic shows otherwise by the way. Note pin 8. The MK41T56 IC accepts voltages from 3-7V on pin 8. It's being supplied 5V. Wow. How did they get 5VDC out of 120VAC?!? 



> With the setup taking time signals from the satellite the time only needs to be accurate on the half hour. With no battery the clock will lose time. The clock chip does store the date also.


That's faulty logic. Really, I think you should try it if you believe that a dead 2032 battery will affect your units while they are powered via AC. Just pull the 2032 cell out while the unit is on. You could even short the battery holder contacts and it still doesn't affect the oscillation frequency.

The point of *you* performing this test is that you feel that new batteries make a difference AND you aren't reporting any problems. 
I'm already the other part of the test since I'm not reporting problems either and I've never changed my batteries. Others in this thread are already the third part of the test since they are reporting problems.
If those with problems replace batteries and the problem persists OR goes away, it won't disprove your theory because there are many other possible causes.

BTW, The typical draw on the 2032 battery from the MK41T56 IC is 450*nA* which is about 10 years.

Seriously, I'm not trying to be a jerk about all of this, but it gets tiring to have someone spout incorrect information that will end as a wild goose chase when someone is trying to figure out why their recordings aren't starting on time.

I know that you are usually trying to help and that's why 99% of the time I keep my mouth shut. I suggest that you keep in mind that not everyone here is clueless about this stuff.


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## rbtravis (Aug 9, 2005)

Tivo uses an M41T00 which according to the manufactures spec's :
"Typical data retention time is in excess of 5 years
with a 50mA/h 3V lithium cell (see Data Retention
Mode, page 13 for AC/DC Characteristics). The
M41T00 is supplied in 8 lead Plastic Small Outline
package."
© 2002 STMicroelectronics - All Rights Reserved

The chip is located at U55 on the tivo motherboard.

The entire data sheet is here:
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/6100.pdf


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## Trent Bates (Dec 17, 2001)

So, they replaced the MK41T56 with the M41T00 later on. MK41T56 could run over 10 years on a 3V cell while M41T00 can run over 5 years. 
Pinouts are the same. Vss (4) and Vcc (8) are still there for 5V supply while Vss (4) and Vbat (3) are there for the 3V battery. Oscillator runs at the same frequency as well.

None of this suggests that the battery must be in good shape or present to keep the time accurate. It shows that both the MK41T56 and the newer M41T00 are supplied 5V from the mainboard to power the RTC and that a 3V battery is used to retain the clock when the 5V power is removed from the circuit.

To be clear about this: The drain on the battery is present when 5V is not present on pin 8.


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## bitmap (Feb 17, 2002)

So to summarize, its not the clock chip, but the DTV signal which is off.

I've noticed the same thing, and at one point, had set my systems to update with ntpdate at two minutes before every half-hour, but of course they always drift again within minutes. As evidenced by the major time warp a few days ago, separate satellites can send different times streams, so tuning to another channel can cause a jump of some minutes in certain cases.

Once I started using endpadplus, to add a few minutes before and after each recording, I stopped worrying about the clock being right, because realistically, its nothing I can fix.


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## Richard R1 (Sep 20, 2002)

The incorrect TIVO clock seems to have been corrected sometime in the past 12 hours or so. Earlier Monday evening, during the 7:00 - 10:00 CDT time period, each of my shows were still missing the first minute or so. This happened with Chuck, 24, and Castle. (Right now, someone is probably asking why I just didn't start my recordings one minute early -- I have another known problem, a defective tuner 2 condition on my Hughes DVR2 which effectively leaves me with only one good tuner. If consecutive shows are set to start one minute early, the next show will start recording on the bad tuner).

Anyway, around 4:00 AM Tuesday, less than two hours ago, I observed the TIVO time was virtually correct -- maybe off by only 2 seconds or less. There seemed to be no difference between local channels or national ones.


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## rbtravis (Aug 9, 2005)

Richard R1:
CCS corp can fix your tuner:
http://www.ccscorporation.net/dss.htm
fixed rate to fix anything wrong with your TiVo including tuner repair except Hard drives
the green thing to do


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## Richard R1 (Sep 20, 2002)

rbtravis said:


> Richard R1:
> CCS corp can fix your tuner:
> http://www.ccscorporation.net/dss.htm
> fixed rate to fix anything wrong with your TiVo including tuner repair except Hard drives
> the green thing to do


Yes, I plan to send it to them soon. I have been looking for the original box in my garage, but haven't found it yet. Perhaps I should get out there again.....


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## Curtis (Dec 2, 2003)

Richard R1 said:


> The incorrect TIVO clock seems to have been corrected sometime in the past 12 hours or so.


My local channels still have a clock that's one minute slow.


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