Welch Allyn Micro Tymp 1, Service Manual

Page: 35 / 82

Section 3.1 Service
M I C R O T Y M P 1 T R O U B L E S H O O T I N G
To reassemble the printer, put the new head on and slide the shafts back in place. Push the gasket ring
on the end of the grooved shaft. Press the gears back on the end of the shafts – the flat gear on the
grooved shaft, the double gear on the smooth shaft – then press the pin into the gear. Slide the head
along the shaft until the hole in the top is lined up with the a cross groove. Push the top pin in making
sure it sits flush with the top of the head. Press the other pin in the side of the printer head, and plug the
flex into the 20 pin connector. Assemble the printer/charger to the point where the top housing and the
bottom plate are ready to be screwed on. The boards will be strapped in the housing with the wire tie
and the power cord wires (black, white, and green or brown, blue, and yellow/green) will be tightened
securely into the terminal block. Plug in the 4 pin wire jack that connects to the power supply board,
coming from the charge and data contacts (containing the red, black, blue, and yellow wires). Recheck
to see that the unit is assembled to this point before proceeding.
WARNING: Setting printer contrast requires working on disassembled unit while it is powered.
Care must be taken to prevent electrical shock.
To set printer contrast you will need a frequency counter or an oscilloscope. Using a frequency counter,
set it to the 10 khz scale. Using an oscilloscope set the volts/div scale to 1 and the time/div scale to 20
microseconds. Hook up clip leads/scope probe from the frequency counter or the oscilloscope by con-
necting the ground lead to the negative side of C1 capacitor. Clip the other lead to pin 8 of the
CD4069UBE chip, making sure not to short any pins (see fig. page 13).
Check the letter on the underside of the flex circuit where the flex goes into the head of the printer. It
will be an A, B, or C. With your frequency counter now hooked up, plug the printer/charger into a wall
outlet. CAUTION: After plugging printer/charger in do not touch any electrical components to
prevent electrical shock.
Place a handle containing data into the printer/charger and push the print button. With a screwdriver
adjust the potentiometer R2 (see fig. page 13) so that the frequency falls within the range of the letter
indicated on the printer (see chart below).
Letter A 9.8 - 10.0 khz
Letter B 10.9 - 11.1 khz
Letter C 12.0 - 12.2 khz
If using an oscilloscope, measure time from the beginning of the first pulse to the beginning of the
second pulse. Adjust the potentiometer R2 until the valve falls within the correct range. Frequency=1/
time, so invert the reading and multiply by 1000 to get khz. Unplug the power cord. Fully assemble
the stand and check operation.
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