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Old 8th Feb 2019, 11:01 am   #2
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: HP T141 Display section repair

They likely are standard resistor values

The nice thing about standards as they say is that there are so many to choose from

HP standardised on 1% resistors in its instrument divisions. Other tolerances were used in special circumstances.

1% resistors have 96 values per decade for the +/-1% tolerance bounds to just meet up with no gaps or overlap. This way, every resistor made can be flogged as one value or another!

96 values per decade are too many for general use, so they picked the ones in the E96 family closest to the common E24 series

1.00
1.10
1.21
1.33
1.47
1.62
1.78
1.96
2.15
2.37
2.61
2.87
3.16

You can generate the E96 values by taking the 96th root of 10 and then keeping multiplying it into a geometric series. Round to two decimal places. For HP's preferred values, skip three out of every four up the E96 series.

2% resistors fit the E48 series
5% jobs got the E24 series (24th root of 10)
10% jobs got the E12 series.

For confusion, some resistor suppliers make 1% resistors (because accuracy is now a lot easier to achieve) but in the E24 2-digit numbers because some customers were confused.by the extra band on the colour code... oh, well.

Cheers
David
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