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Old 11-21-2012, 05:42 PM   #1
mrbenjie
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CHEAP replacement fan for series 2?

I have a Series 2 and the fan has stopped working.

Checked with WeakKnees but they want about $20 + shipping for a fan, which feels like I am getting ripped off, since I know you can get computer fans for about $5-7.

What I don't know is the exact specs I need in a replacement, or a specific one that will work with this model.

Any ideas? Thanks much!
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Old 11-21-2012, 06:21 PM   #2
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Quote:
Originally Posted by mrbenjie View Post
I have a Series 2 and the fan has stopped working.

Checked with WeakKnees but they want about $20 + shipping for a fan, which feels like I am getting ripped off, since I know you can get computer fans for about $5-7.

What I don't know is the exact specs I need in a replacement, or a specific one that will work with this model.

Any ideas? Thanks much!
any 60 x 60 x 25 mm fan will do.

for example

http://www.amazon.com/Vantec-Stealth.../dp/B000234W04
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Old 11-21-2012, 06:28 PM   #3
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# of pins?

Most of these have 3 pin connectors, but Tivo fan connection on motherboard is 2. Will this work and if so, how do I connect it?

Thanks!
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Old 11-21-2012, 07:38 PM   #4
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http://www.ebay.com/itm/Y-S-Tech-NYW...item5aeae296a4
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Old 11-21-2012, 08:08 PM   #5
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You position the plug so that the red and black wires are connected and the end with the yellow wire hangs off the end. When I was swapping in fans, I was a big fan of ADDA fans. But that Vantec Stealth looks like a good bet.

One issue is that the TiVo puts out about 7V on the fan pins so that the fan doesn't run at full speed. Some fans won't run at that low a voltage.
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Old 11-21-2012, 11:16 PM   #6
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Quote:
Originally Posted by mrbenjie View Post
I have a Series 2 and the fan has stopped working.

Checked with WeakKnees but they want about $20 + shipping for a fan, which feels like I am getting ripped off, since I know you can get computer fans for about $5-7.

What I don't know is the exact specs I need in a replacement, or a specific one that will work with this model.

Any ideas? Thanks much!
Its a 70mm x 70mm x 25mm fan and you can use it even if the wires are 3+ since it only uses the red and black, the white is ignored.

The previous poster mentioning a 60mm x60mm fan is for the Premiere.
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Old 11-22-2012, 12:42 AM   #7
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Quote:
Originally Posted by stevel View Post
You position the plug so that the red and black wires are connected and the end with the yellow wire hangs off the end. When I was swapping in fans, I was a big fan of ADDA fans. But that Vantec Stealth looks like a good bet.

One issue is that the TiVo puts out about 7V on the fan pins so that the fan doesn't run at full speed. Some fans won't run at that low a voltage.
Are you quite certain that you are correct?

It was my understanding that it uses Pulse-Width Modulation, where it puts a full +12V across the line, but only for a short time, and then nothing, and then +12V again, lather, rinse, repeat, so that the average voltage is less than +12, but each pulse is a full +12, which overcomes the motor's mechanical inertia, then leaves it to coast, then gooses it again, over and over.
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Old 11-22-2012, 01:34 AM   #8
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Quote:
Originally Posted by mrbenjie View Post
I have a Series 2 and the fan has stopped working.

Checked with WeakKnees but they want about $20 + shipping for a fan, which feels like I am getting ripped off, since I know you can get computer fans for about $5-7.

What I don't know is the exact specs I need in a replacement, or a specific one that will work with this model.

Any ideas? Thanks much!
If you're really cheap (like me), you can possibly revive it.

If you have a similar size fan in your computer junk box, hook it up and make sure that the TiVo motherboard is still putting out current on that 2 pin header when a good fan is connected.

And similarly test the TiVo fan elsewhere.


The fan blows from the blade side to the "support" side.

On the support side, you can peel back the label, and possibly remove a plug, and then remove (carefully) the little washer thing that goes over the end of the blade assembly axle and pull the blade assembly off.

Then you can use some de-natured alcohol, or maybe lighter fluid, to clean the axle and the hole it went through of the old lubricant.

Then you can use a combination of light grease (ignition tune-up grease, fishing reel grease, etc) and light oil (sewing machine oil, 3 in 1, etc) to re-lubricate.

This assumes that the electrical part of the fan is still good.
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Old 11-22-2012, 06:46 AM   #9
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Quote:
Originally Posted by unitron View Post

Are you quite certain that you are correct?

It was my understanding that it uses Pulse-Width Modulation, where it puts a full +12V across the line, but only for a short time, and then nothing, and then +12V again, lather, rinse, repeat, so that the average voltage is less than +12, but each pulse is a full +12, which overcomes the motor's mechanical inertia, then leaves it to coast, then gooses it again, over and over.
What I wrote was correct for the Series 1 and Series 2 boxes. Maybe newer ones are different, but if the connector is only two pins, then I am pretty sure it's still accurate. But not "quite certain".
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Old 11-22-2012, 09:12 AM   #10
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bet.

One issue is that the TiVo puts out about 7V on the fan pins so that the fan doesn't run at full speed. Some fans won't run at that low a voltage.
I too had read that the motherboard only puts out 7V. I replaced my Series 2 fan with a Vantec unit and used the included molex adapter to connect it to the hard drive power connector which supplied 12 V. It was a tad noisier but not so much you could really notice. Kept temps lower.
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Old 11-22-2012, 10:44 AM   #11
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Quote:
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Are you quite certain that you are correct?

It was my understanding that it uses Pulse-Width Modulation, where it puts a full +12V across the line, but only for a short time, and then nothing, and then +12V again, lather, rinse, repeat, so that the average voltage is less than +12, but each pulse is a full +12, which overcomes the motor's mechanical inertia, then leaves it to coast, then gooses it again, over and over.
Quote:
Originally Posted by stevel View Post
What I wrote was correct for the Series 1 and Series 2 boxes. Maybe newer ones are different, but if the connector is only two pins, then I am pretty sure it's still accurate. But not "quite certain".
You may both be correct. Indeed, at some level, you both definitely are. The fans used by computers are brushless DC motors controlled by a small embedded integrated circuit. Without going into detail about the motors themselves, the fan speed is more or less proportional to the input voltage. The fan motor itself is synchronous, but the fan as a whole is not. If the motor itself were being driven by a PWM input, then the PWM would have to be synchronized with the motor's rotation, or the motor would not run very efficiently, or perhaps even stall or chatter, rather than rotate. PWM DC is also not a very good way to run a synchronous motor.

In any case, what is most relevant to the fan's speed is not the waveform, but the RMS voltage. If a signal is steady-state DC, then its RMS voltage and its DC voltage are the same. If the waveform is one that drops from time to time away from the peak voltage, then the RMS voltage also drops. Thus, if we have a square wave with a peak voltage of 12V, and the marks and spaces in the waveform are equal in duration, then we have an 8.49Vrms signal. Measured with an appropriate type of voltmeter, it will indeed read 8.49V. Under no load, if we simply take a capacitor and place it across the leads, it will read 12V, but if we load the signal, the measured voltage will drop toward 8.49V. If we look at the waveform, it is no longer a series of pulses, but rather a sort of lumpish pseudo-sine wave with about an 8.49V DC bias. In fact, what we have is an unregulated switching power supply. If we narrow or widen the spaces, leaving the positive marks unchanged, then the output voltage will increase or decrease, respectively.

No matter what the signal looks like, the motherboard will create the signal by simply producing a series of pulses on the line. They may well design the board with some filter capacitors on it, but since the fans don't really care one way or the other, I somewhat doubt it. Either way, when we speak of a 7V fan voltage, we are talking about the RMS voltage, and not really saying much about the actual waveform. The fan will be happy with either one.

Unitron,

Your description of the action of the motor vs. the input signal is essentially correct, but as long as the mass of the fan rotor is fairly large compared to the width of the pulses, the effect is nearly indistinguishable from a steady-state DC input voltage. Since it is only a fan, at the practical level, we really don't care about the distinction. The fan's electronics don't care too much, either, except that a lower voltage PWM signal may be able to overcome the fan's inertia and static friction to start it spinning than a pure DC input, and a pulsed DC input may be more efficient than a steady-state voltage of a lower value.

Last edited by lrhorer : 11-22-2012 at 10:51 AM.
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Old 11-22-2012, 08:40 PM   #12
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I had also heard Tivo utilizes the fan by pulsing the DC signal except at start up.
I presume the Tivo runs the fan at full speed on start up to get it rotating, then at some point reduces the rms voltage via PWM.
I remember early Premieres having a problem with the fan chattering. Solution was to put a small capacitor in parallel with the fan.
Another thing to consider is the fan's lubrication. If the lubrication is insufficient, the fan might not be able to sustain rotation under PWM and could eventually stall.
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Old 11-23-2012, 06:21 PM   #13
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Its a 70mm x 70mm x 25mm fan and you can use it even if the wires are 3+ since it only uses the red and black, the white is ignored.

The previous poster mentioning a 60mm x60mm fan is for the Premiere.
i'm looking at one right now and it is 60mm x 60mm x 25mm. It's a superflo model AUB0612L with the original 2 pin connector
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Old 11-23-2012, 06:23 PM   #14
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i'm looking at one right now and it is 60mm x 60mm x 25mm. It's a superflo model AUB0612L with the original 2 pin connector
That won't fit a Series 2.
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Old 11-23-2012, 06:47 PM   #15
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That won't fit a Series 2.
It does fit and the fan which replaced it is a vantec stealth SF6025L also 60 by 60 by 25 but with a 3 pin connector using only the red and black and that also fits.

I just opened up a series 2 and used a ruler.

Okay -- having done a quick search on weaknees, I see there are 2 different replacement fans for most series 2 tivos depending on whether or not the back grill is flat or raised. My fan grill is a flat back surface and uses a fan with the dimensions cited. If the fan grill in back of tivo has a raised profile, then it may fit different dimensions. I can't speak to that as don't have a series 2 with a raised fan grill.

Last edited by poppagene : 11-23-2012 at 07:03 PM.
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Old 11-23-2012, 07:03 PM   #16
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Going by what I've got the lids off of currently:

S1 80x80x25

S2 DT 70x70x25

S3 OLED and S3 HD 70x70x25


http://www.allelectronics.com/

has some 80s and 60s right now, the only 70 is a Pentium4 heatsink/fan combo, but they're a surplus dealer, so a week from now they might have tons of them.
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Old 11-23-2012, 07:08 PM   #17
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It turns out that

http://www.tivopedia.com/


lists fan sizes by model.
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Old 11-24-2012, 10:21 PM   #18
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I had also heard Tivo utilizes the fan by pulsing the DC signal except at start up.
That is really just semantics. A PWM signal with a 0 space interval is the same thing as DC, or to put it another way, maxing out the PWM signal power results in a DC waveform.

Quote:
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I presume the Tivo runs the fan at full speed on start up to get it rotating, then at some point reduces the rms voltage via PWM.
Or one can say it starts out with the PWM signal at maximum power and reduces it later. It's is a bit more in line with the actual underlying electronic mechanism.

I rather doubt the TiVo is specifically designed with fan stall in mind. If the fan starts at high speed and later the speed drops, it is likely because the software that controls the fan speed (by reducing the input voltage) is not yet running. It's a failsafe mode that keeps the electronics from frying if the software never comes online, presumably because of a failed hard drive.

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I remember early Premieres having a problem with the fan chattering. Solution was to put a small capacitor in parallel with the fan.
I don't doubt that, at all.

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Another thing to consider is the fan's lubrication. If the lubrication is insufficient, the fan might not be able to sustain rotation under PWM and could eventually stall.
Here I am not sure what you mean. The fan is more likely to stall under a 7Vrms PWM input than a 7VDC steady-state input. To be sure, it is somewhat more likely to stall under a 7V input than a 12V input, regardless of the waveform.
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Old 11-25-2012, 12:20 AM   #19
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That is really just semantics. A PWM signal with a 0 space interval is the same thing as DC, or to put it another way, maxing out the PWM signal power results in a DC waveform.
Pulse Width Modulation starts with x number of equal length pulses per second and adjusts the duty cycle to get the desired overall power level while maintaining the initial "kick in the pants" of the voltage of the "on" part of the duty cycle.

When the TiVo first boots, the duty cycle is 100%. It's all "on" part and no "off" part at that point.


Quote:
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Here I am not sure what you mean. The fan is more likely to stall under a 7Vrms PWM input than a 7VDC steady-state input. To be sure, it is somewhat more likely to stall under a 7V input than a 12V input, regardless of the waveform.
If by 7Vrms PWM input you mean a 12V input with parts chopped out, i.e., 12V, but a duty cycle less enough than 100% to produce an rms "average" of 7V, I'd think the inertia-overcoming power of the 12V of the leading edge of the on portion of the pulse would better prevent stalling.

(pretend an instantaneous rise time, to keep things simple)

Of course this presupposes the designers chose the correct overall length, time-wise, i.e., the right frequency, for the pulses whose width they proposed to vary.
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Old 11-25-2012, 03:24 AM   #20
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Pulse Width Modulation starts with x number of equal length pulses per second and adjusts the duty cycle to get the desired overall power level while maintaining the initial "kick in the pants" of the voltage of the "on" part of the duty cycle.
It can be a fixed mark width with a variable space width, or a fixed period with variable space and mark intervals. Note the latter does allow for a greater range of voltage levels, but I have seen both in power supply designs.

Quote:
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If by 7Vrms PWM input you mean a 12V input with parts chopped out, i.e., 12V, but a duty cycle less enough than 100% to produce an rms "average" of 7V, I'd think the inertia-overcoming power of the 12V of the leading edge of the on portion of the pulse would better prevent stalling.
Yeah, I already said that. If the mark and space width are the same (50% duty cycle, as you put it), it's 8.49V, assuming a 12.0V peak.

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Of course this presupposes the designers chose the correct overall length, time-wise, i.e., the right frequency, for the pulses whose width they proposed to vary.
Yes, but that is not difficult. Anything from a few hundred Hz to a few hundred KHz should be fine.
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Old 11-28-2012, 11:58 PM   #21
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Thank you! It works :-)

Thanks all for the advice! (Lots of smart folks on this forum, clearly.)

I'm no electrical engineer, so instead of trying to follow all the posts in this thread, I just bought a fan and installed it from one of the links to see what would happen.

Put in a Vantec Stealth SF6025L (suggested by poppagene) for $9.78 shipped. (WAY less than some companies were trying to charge me.)

Fan is so quiet I didn't know if it was working or not. But the results tell me it is.

TiVo WAS overheating constantly, unless I set a paper towel with a few Tupperware trays on top of it, with frozen solid water bottles sitting in them (a poor man's heat sink). This would usually hold it for 8 hrs until I swapped out the next batch of frozen water bottles, so at least I could use the TiVo.

Now, has been running for over 24 hours with NO overheating, and system info indicates internal temperature is normal.... so, works great! (Still can't hear the fan at all.)

Did exactly as suggested (by stevel) re installing the fan (put 3 pin connector over 2 pin on motherboard so the yellow wire not connected), and seems to work fine running off the motherboard without having to get tricky.

Thanks again for the great suggestions!
:-)
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Old 11-29-2012, 12:17 AM   #22
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Glad you got that remedied.

Although the Tivo model was not mentioned, various Series 2 models use either the 60x60x25 or the 70x70x25 fan sizes.
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