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Quick question about the 71b - Printable Version

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Quick question about the 71b - Geoff Quickfall - 05-01-2008

Actually, two questions:

1. there are three slotted screws on the back of the older metal backed HP 71B's. Two must be removed and are placed vertically to one side. The third is attached to the circuit board inside via a nut. It does not have to be removed to separate the two halves of the computer. My question is, after searching the site and talking to Tony Duell is; what is the purpose of this screw and nut other than support. It does not control a trimming capacitor or anything else, so why so many admonitions not to move it?

2. My card reader is EXTREMELY finicky when it comes to differentiating "TOO SLOW versus TO FAST". Is it just practice or is there away to expand the window for the correct speed. I am running about 10% successful on my card read write operations.

Thats, it, got to go now.

Cheers, Geoff


Edited: 1 May 2008, 8:45 p.m.


Re: Quick question about the 71b - Raymond Del Tondo - 05-01-2008

Hi Geoff,

you have mail:-)

Cheers

Raymond


Re: Quick question about the 71b - Maximilian Hohmann - 05-02-2008

Hello!

Quote:
you have mail:-)

Why mail? I would have been very interested in answer no.2, because I have the same problem with my 75C...

Greetings, Max


Re: Quick question about the 71b - Geoff Quickfall - 05-02-2008

The mail was private but also included an explanation that practice was required to get it right. I must admit the success rate is increasing.

Part of the explanation also centered on a dirty reading head. Try using the abrasive card once or twice to confirm the head is clean after all these years. I also cut out a piece of construction paper the same width and thickness of the cards and then applied a liberal amount of isopropyl alcohol to it. I then ran this through the reader along with a dry one and the reader seems to function better, or it may be my technique!

Cheers. Geoff

Edited: 2 May 2008, 1:13 p.m.


Re: Quick question about the 71b - Diego Diaz - 05-02-2008

Hi there,

Seems that you're on the good path regarding your question nr. 2.

About your question nr. 1, these tree screws are itended por EMI screening/shielding.(Electro Magnetic Interference... you sure have read it before: "FCC rules, part 15, subpart J"... ;-))

The longer and most centered one (with a small nut inside the HP-71B) connects the mainboard GrouND to the plate on the bottom of the HP-71B, while the other two connect this plate to the display bezel and the keyboard template respectively. Thus the mainboard becomes into a "sandwich" (kind of) between grounded plates reducing both EMI emissions and sensitivity to external interferences.

Hope this clarifies it a bit.

Cheers!

Diego.




Thanks Diego, - Geoff Quickfall - 05-02-2008

When I took the HP71B apart to give it a good clean I asked Tony Duell in an email about the screws. He stated as have a few 71B postings over the last few years to not touch the centre one.

It just appeared that there was more to it then just a connecting screw. That it might be used in adjusting something! When I had it apart I noticed all it did was ground out the metal back to the circuit board much the way many contact springs due in digital watches.

Thanks for the EMI explanation. I feel better now as it was the 5 screw I started to undo when I got the computer!

Cheers, Geoff