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Old 28th Sep 2020, 12:35 am   #41
Skywave
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Arrow Re: HP 8640B displayed freq. is wrong

Re: my post #27.

As a wrote in that post, it is difficult to put into clear wording the bit about the block connector which is located between the motherboard and the time-base board.

Attached is a sketch - that hopefully makes things clearer.

Al.
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Old 28th Sep 2020, 7:37 am   #42
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Default Re: HP 8640B displayed freq. is wrong

Al,

yes, I have vague recollections of that rather strange arrangement when I was working on mine. You said in the earlier post that your "cleaned and polished" the block connector - did you use anything specific to do the cleaning? Isopropylalcohol or something similar?

As I recall it was a way of allowing significant variation in the position of the two boards being connected without going to bother of using a multiway flexible cable. I think these connectors later evolved in the "zebra strip" used on LCD panels, where there are alternating bands of conductive and non-conductive rubber - picture enclosed.

All one can say in its favour is this type of arrangement can work, and obviously does while dirt is held at bay.


Richard
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Old 28th Sep 2020, 9:52 am   #43
Skywave
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Default Re: HP 8640B displayed freq. is wrong

I cleaned the contact wires on that block connector and the pcb tracks using metal polish (Solvol Autosol) followed by a wash with I.P.A.

I still feel that that chosen approach to making an inter-board connector by using that method was a poor design idea. A back-to back female edge connector would have been much preferable with suitable RF screening. O.K., so that would probably have meant using a custom designed part, but the 8640 is full of such custom-made parts, anyway.

Al.
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Old 28th Sep 2020, 11:01 am   #44
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Default Re: HP 8640B displayed freq. is wrong

Quote:
Originally Posted by Skywave View Post
but the 8640 is full of such custom-made parts, anyway.
It had to be, it was designed before parts of those natures entered the mainstream. You're looking at one of the fore-runners of a lot of RF technology that we take for granted.

Something like the 8640 is becoming harder to do again. Yes we have amazingly fast logic, but it's all locked away inside CPUs and other complex ASICs. It's remarkably hard to buy a single quick flip-flop. Some can be found at Hittite, but look at the prices!

Hittite are now owned by Analog devices. With Hittite's biblical name, I always thought they ought to have the slogan "Devices with which to smite thine competitors"

David
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Old 28th Sep 2020, 8:24 pm   #45
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Default Re: HP 8640B displayed freq. is wrong

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Quote:
Originally Posted by trh01uk View Post
Looking at the number of ways on those connectors, and the avoidance of exact board alignment, no doubt the original designer would respond to all this criticism with a "seemed like a good idea at the time" type of comment!

Richard
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David
I imagine there was probably a mention in one of the Journals about how great the design of the Square section connector was, together with the instrument it was designed for, it wasn't the 8640A/B as it predates it.

It is used in a few early 1970's counters in my collection, there is version that wire looms can be soldered to (picture from HP K20-5280A);
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Plus they can be used to connect & mount two boards at right angles (used in HP 5326/7 series, picture from 5326B);
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