As an EA-1 ages, or when replacing a circuit board, it may be necessary to adjust the range-counter adjustment potentionmeter. Even though each board is tested and calibrated before leaving the factory, small differences between balances may call for this adjustment.
To check the counter, range follow the procedure below: (The balance should be fully assembled with all covers on.)
1. Turn on the power switch and make sure that the pilot light is on. Let the balance “warm up” for 15 minutes.
2. Set all weight control knobs to zero and rotate the counter control knob to 000 on the counter. Bring the null indicator needle to the center line or null by operating the coarse tare and zero adjustment knobs.
3. Place a 100 mg. class S wight on the balance pan, close the balance door, and operate the counter control knob to a setting of 999. The null indicator needle
should come to rest at center or within a needle width to the left of center. If the instrument does not operate as outlined above, refer to COUNTER ADJUSTMENT PROCEDURE.
If class S 100 mg. weight is not available, place a small object, such as a ten cent piece, on the balance pan and make a mass determination as described under “Weighing Procedure,” except that the counter should be left at zero and the needle brought to null by manipulating the coarse tare control and zero adjustment knobs. If the number on the weight control knob to the right of the decimal point is between one and nine, reduce this number by one and then rotate the counter knob to set the countei at 999. The null indicator needle should be at center or not more than a needle width to the left of center. If the instrument does not operate as outlined above, refer to COUNTER ADJUSTMENT PROCEDURE.
TO SET RANGE – COUNTER ADJUSTMENT PROCEDURE
If, in checking the counter range as described above, the counter setting of 999 causes the pointer to be more than a pointer width to the left or at any point to the right of null, it will be necessary to adjust the range control potentionmeter. (An access hole is provided in the lower portion of the rear shroud of the balance.) Use a screwdriver and rotate the slotted shaft slowly until the pointer returns to the null position.
Reset the counter to 000, remove the 100 mg weight or advance the right weight control knob one number, and use the zero adjust knob to place the needle at null. Repeat the test and readjust if required.
Even though the “Range” remains constant for extended periods, it is good weighing practice to check it periodically and adjust if necessary.