Olympus BH-2 BHT Manual - Halaman 6

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extinguishing the 6V LED. If the setting of the intensity control is decreased to the point where the clamped control

signal exceeds the threshold waveform, the 6V LED will completely extinguish. The operation of the remaining three

comparators is similar to this one, differing only in their threshold voltages.

Power LED

Resistor R203 and LED "A" function as the power‐on indicator for the microscope.

Errors in the Olympus Documentation

In the course of researching this document, two errors were identified in the schematic diagram published in the

Olympus Research Microscope Series BH2 (BHS) Repair Manual. Both of these errors are in the LED bar‐graph display

circuitry.

Bar‐Graph LEDs

The first error is in the wiring of the four bar‐graph LEDs, as shown in Detail 1 of Appendix 2 and Appendix 3 of this

document. The Olympus manual shows these LEDs wired with their cathodes connecting to their respective comparator

outputs and with their anodes wired to their respective current‐limiting resistors. The actual circuit configuration (as

observed on the main boards of functional BHTU equipment) has the anodes of the four LEDs connected to the filtered

DC power supply line and the cathodes connected to their respective current‐limiting resistors. This is a minor

discrepancy and either configuration would work equally well, but the actual as‐built configuration is shown in this

document.

Control‐Signal Clamping Network

The second error is in the wiring of the control‐signal clamping network, as shown in Detail 2 of Appendix 2 and

Appendix 3 of this document. The Olympus manual shows this network fed from the full‐wave‐rectified output of the

bridge rectifier, but in the actual circuit configuration (as observed on the main boards of functional BHTU equipment),

this network is fed from the filtered DC power supply line. This error is of greater consequence than the first, as the

circuit published in the Olympus repair manual would not guarantee that the LEDs remain off around the zero crossings

of the AC line.

Removing the Electrical Base from the Stand

To gain access to the electronics in the base of the BHT/BHTU stand, the electrical base must be removed from the base

of the stand. Be sure to take sufficient notes and plenty of photographs both before and during the disassembly process

to make sure that everything can be correctly reassembled later on. Before removing the electrical base, look at the

right‐hand side of the unit, just above the intensity slider, and note whether or not a light preset control and switch are

present. The earlier units did not include these components, but the later ones did.

Next, remove all the major components from the microscope stand (i.e., AC power cord, condenser, stage, eyepieces,

viewing head, and objectives). Doing so will make the stand easier to maneuver and will prevent inadvertent damage to

these components during disassembly and reassembly. Be sure to protect these components from dust and damage

while they are not installed on the stand.

After removing these components, cover the top of the arm (i.e., the nosepiece turret and the exposed mounting

dovetail for the viewing head) with a clean plastic bag and secure this with a rubber band to keep dust out of these

openings. This is especially important on BHTU stands which have an optical correction lens located just below the

viewing head to correct for the difference in tube length introduced with the reversed nosepiece.

With the stand in its normal upright position, remove the lamp house from the back of the base. The lamp house simply

plugs into the base, and can be removed by grasping it and pulling it straight back. Set the lamp house aside to prevent

damage. Do not touch the halogen lamp with your fingers, as oils from your skin will cause premature failure of the

bulb. If the bulb is accidentally touched, clean it with isopropyl alcohol.

Carefully turn the stand upside down, exercising caution to prevent impacts to the focus knobs and to the

condenser/stage holder. Using a 5/32" Allen tool, remove the four hex socket‐head cap screws from the bottom of the

Olympus BH‐2 (BHT/BHTU) Electronics

Revision 2

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