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Electronics => Repair => Topic started by: iXod on July 04, 2016, 12:12:18 am

Title: HP 34401A dmm repair -- general schematics question
Post by: iXod on July 04, 2016, 12:12:18 am

http://imgur.com/KWFIN1H (http://imgur.com/KWFIN1H)

Pins 12 and 13 have a little triangle next to the pin number; pins 1, 2, 15, 16 have what looks like an "n"; 3 and 14 have an "x".

What's the meaning of these marks?

Thanks.

Title: Re: HP 34401A dmm repair -- general schematics question
Post by: Dr. Frank on July 04, 2016, 06:39:44 am

Quote from: iXod on July 04, 2016, 12:12:18 am

http://imgur.com/KWFIN1H (http://imgur.com/KWFIN1H)

Pins 12 and 13 have a little triangle next to the pin number; pins 1, 2, 15, 16 have what looks like an "n"; 3 and 14 have an "x".

What's the meaning of these marks?

Thanks.

These triangles usually denote digital inverting inputs; in the AD7524 datasheet, it's /Chip Select and /Write.

These small 'n' may denote a guard ring around all these 4 analogue pins, but that's my speculation only. Never noticed that before.
I'll have a look into the original, 1990 vintage schematics, which look a bit different.

Frank