Invisible wrote:
> Actually, I have three of them. And you know what? They're all slightly 
> different...
> 
> If I compare any pair of boards, there is a difference. So it's not like 
> one board is different to the other two, they're ALL different!
> 
> - Boards B and C have two RAM chips on them. Board A has bays for two 
> chips, but only one is present. (All three boards are spec'd as "4 MB".)
> 
> - Board B has a different brand of RAM chip. (But *all* the boards have 
> different *models* of RAM chip.)
> 
> - Boards A and C have pins on the AGP connector which aren't connected 
> to anything. But on board B, those pins are physically missing rather 
> than just unconnected.
> 
> - Board B has less writing printed on it between the two RAM chips. The 
> actual components mounted there appear identical, but just fewer markings.
> 
> - Each board has some kind of 3-pin component with what looks like a 
> heat sink soldered to a very large metal pad on the board. Oddly, only 
> two of the three pins are connected to anything; the middle pin is cut 
> off at the base. On boards A and C, there are three metal pads on the 
> board that end in rounded tips, and the middle one appears to be a 
> continuation of the large pad the heat sink is soldered to. But on board 
> B, there is a gap between the pads the pins are soldered to and the 
> circles at the end, and there is no middle pad (but the circle is still 
> there).
> 
> - Some of the code numbers on both the S3 chip and the Holtek chip are 
> different on each board, while others are identical. (I'm guessing these 
> are serial numbers, or at least revision numbers.)
> 
> - Hello, I didn't notice this: Board B says "SP368G REV:2" on it, while 
> the other two boards say "SP368G REV:3" on them.
> 
> So there we are. *Clearly* I have too much free time...

...business as usual, eh? :-} Some things never change...

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> So my next question is... why does a digital device require so many 
> millions of resisters and capacitors?

Can't say for all designs, but I know on our LCD electrical designs it is 
mainly for noise-reduction and filtering.  If we didn't filter the digital 
signals, especially the ones on long tracks, we would be above the EMC noise 
limits allowed.  In a car in particular, the FM receiver circuitry is 
usually right next to the LCD, so the 85-110 MHz band is extra important, I 
imagine most consumer devices have similar requirements.

> (Maybe millions is an exaggeration, but there sure is a lot of them 
> here... Big ones, tiny ones... I assume the tiny ones *must* be mounted by 
> machine?)

It's done by a "pick&place" machine:

http://www.youtube.com/watch?v=M7w5OUXwTZs
http://www.youtube.com/watch?v=6NamGXOgb5s

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>> So my next question is... why does a digital device require so many 
>> millions of resisters and capacitors?
> 
> Can't say for all designs, but I know on our LCD electrical designs it 
> is mainly for noise-reduction and filtering.  If we didn't filter the 
> digital signals, especially the ones on long tracks, we would be above 
> the EMC noise limits allowed.  In a car in particular, the FM receiver 
> circuitry is usually right next to the LCD, so the 85-110 MHz band is 
> extra important, I imagine most consumer devices have similar requirements.

Well, I'm looking at a graphics card, so presumably it's to isolate any 
noise from the AGP bus from the (much lower frequency) video signal?

>> I assume the tiny ones *must* be mounted by machine?
> 
> It's done by a "pick&place" machine:
> 
> http://www.youtube.com/watch?v=M7w5OUXwTZs
> http://www.youtube.com/watch?v=6NamGXOgb5s

That's pretty insane...

Presumably the through-the-hole stuff is done by a human operator. 
(Indeed, I worked on a production line doing that once...) The 
surface-mount stuff is machine. Or that would be my guess anyway...

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> Well, I'm looking at a graphics card, so presumably it's to isolate any 
> noise from the AGP bus from the (much lower frequency) video signal?

Hmmm, my graphics card is churning out (1920*1200 + 1600*1200)*60*24 bits 
per second.  Is the AGP bus higher than that?

> Presumably the through-the-hole stuff is done by a human operator.

I don't know, all our components are surface mount.

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scott wrote:
>> Well, I'm looking at a graphics card, so presumably it's to isolate 
>> any noise from the AGP bus from the (much lower frequency) video signal?
> 
> Hmmm, my graphics card is churning out (1920*1200 + 1600*1200)*60*24 
> bits per second.  Is the AGP bus higher than that?

An antique graphics card can't do that. IIRC, this has a maximum 
resolution of 1024x768, and it's analogue output only.

>> Presumably the through-the-hole stuff is done by a human operator.
> 
> I don't know, all our components are surface mount.

This one has several radial electrolytic capacitors.

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> An antique graphics card can't do that. IIRC, this has a maximum 
> resolution of 1024x768, and it's analogue output only.

I'm sure it's not that low (my first computer 20 years ago could do that), 
but anyway the bit-rates that are input to the DAC (or to the DVI socket on 
newer cards) are quite similar to what is happening on the AGP bus.

Also don't forget the board also needs to protect against ESD, any incoming 
EMI, and also surpress any EMI that might affect other components inside the 
case, or any components outside the case.

> This one has several radial electrolytic capacitors.

I would be surprised if there were not an automated way of mounting them.

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Invisible wrote:
> So my next question is... why does a digital device require so many 
> millions of resisters and capacitors?

Because electronics are analog. The resistors and capacitors is what *makes* 
it digital.

-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

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Invisible wrote:

> 
> ...business as usual, eh? :-} Some things never change...

Interestingly, I had an HDTV tuner board where one of the capacitors (a 
big electrolytic one) was knocked off the board during packaging and 
shipping.

I called the company to inquire about the missing cap. They talked to 
the engineers and concluded that it wasn't necessary for the proper 
operation of the board..

It worked fine, BTW
-- 
~Mike

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Darren New <dne### [at] sanrrcom> wrote:
> Because electronics are analog. The resistors and capacitors is what *makes* 
> it digital.

  And I thought it was the transistors.

-- 
                                                          - Warp

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Because electronics are analog. The resistors and capacitors is what *makes* 
>> it digital.
> 
>   And I thought it was the transistors.

Them too. Transistors are just resistors you can control the resistance of. 
Transistors aren't digital without the resistors. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

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