EEVblog > EEVblog Specific

EEVblog 1404 - The Amazing HP 9845B Computer

(1/4) > >>

The HP9845B 16 bit computer was revolutionary in 1979 and the early 1980's, find out why.
The 9845C colour version of this created the amazing war room images for the movie War Games

I wonder about that computer, at around the same time I used another HP computer that was much more user friendly.
It had a keyboard with a row of soft keys below the CRT. These keys was used to compose commands to the computer. This may not be anything special, but the computer uses a HPIP (Later named GPIB) connection to a harddisk unit to fetch the software needed to perform the command and the harddisk could serve multiple computers. I must admit that I did not really use that computer, a Univac 1100 computer was much more fun to use and I also bough my first home computer at about the same time (A NASCOM2 Z80 based one).
We also had a P-Code machine, that was another type of computer and it has gone completely out of fashion. It was fast at that point in time, but being a very advanced CISC it was sidelined by RISC computers and the base language never got popular enough to maintain it either.

Could someone with more EE skills explain the ferrite beads on capacitors?

My understanding:

 - (ideal) capacitors block DC and likewise form a low pass filter, but inductance lets higher frequencies through.
 - ferrite beads block very high (RF) frequencies, so it's a high frequency low pass filter.

So it's just blocking high, and low, frequencies but not a middle band? So it's a bandpass filter?

There must have been a very specific purpose for having them on every cap, since nobody else does it. And putting them _attached_ to each cap must be for one/both of two reasons:
 - Package convenience instead of populating two slots on the board
 - Extreme locality for minimum... I don't know the EE term... noise/interference between two coupled components.

Anyway, if I'm right/wrong, I'd love someone to give me some background information. Thanks!


Found my answer!

"3-lead capacitor, 0.22UF/ 50V, with ferrite beads on two outer leads. The three-terminal structure decreases residual inductance and greatly improves the noise suppression effect at high frequencies greater than several dozen MHz."

Also interesting is that they can form resonates if you select the wrong values:

I would have loved to put a scope on that thing and see how incredibly noisy it is between the heavy # of jellybean logic ICs and the non-angled traces.

Guarantee those are spacers.  Nice color and shape, wouldn't be surprised if they were stock necklace beads or something? :D

Dave, noticed a couple glitchy pictures, like around 3:49 the computer is on screen for 4 frames then the previous image for 1 then it's alright after that. Hope the rendering's not going funky on ya!



[0] Message Index

[#] Next page

There was an error while thanking
Go to full version