Antares Analytical Technical Bulletin for January 2002

Subject: Possible Loss of High Voltage on the MOA

Relevant Models: All Baird MOA-C, MOA GT, MOA C/GT, MOA-M

Relevant Matrix: Not applicable

Symptoms:

• No reading on the HG Meter when HG adjustment dial is at the last known HG peak alignment position.
• On the MOA-C or MOA-M the burn time goes to 50 seconds, though the MOA-C has been running with 30-32 second burn time consistently. This will happen at once …this is not a “as time goes on” symptom. The MOA GT and MOA GT/C should be running at a fixed 30 second burn time and will not show this symptom.
• On the MOA-GT, loss of H.V. will not cause this 50-second problem as when the MOA-GT is operating with SV2 switch (located on the lower right of the MOA motherboard) put in the CT position.
• Results of a sample analysis after a burn, read all “O” ppm. You run the same sample again in intensity ratio and all the results are 990 to 1010 (more or less) for all elements.

Possible causes of no high voltage:

• HV Fuse:  Check the fuse under the amber colored fuse cover (side panel near main power switch) to be sure it is good. Best results are with an ohm meter and fuse is checked for continuity

• High Voltage Interlock Switch
• Two things can cause this switch not to work ….  Open the rear cover of the optical cell.
• On the upper left side will be a small push type switch and this is the interlock switch for the H.V. supply. It is activated by pressure when the rear optical cell cover is installed and tightened down. Failure of the switch itself - To test: place leads across the switch contacts, push the switch in and look for continuity on your ohmmeter.
• Not enough pressure from the optical cover: - The switch is located between the top left and 2^nd left hold-down screws of the rear optical cover. Tighten both until enough pressure is supplied to activate the switch.

• Check output of High Voltage Power Supply

·         Verify the high voltage power supply is putting out 1005 VDC ….Put the MOA in the OFF position using the main power switch.

·         Open the front electrical panel (only performed by qualified electrical personnel). The high voltage power supply is located in the upper right corner of the electronics bay, surrounded by a protective cage

·         At the back of this cage, coming from the power supply, will be several wires, including two wires, twisted together, which end in a white, two pin, Molex type connector. The –1000 VDC is carried to the PMTs through this cable/connector.

·         Pull the connector apart and insert the leads into female side COMING FROM THE HVS supply … NOT the side going to the optical cell. The voltmeter should to the 1000 VDC scale. Be sure the leads and meter are not touching any part of the spectrometer chassis.

·         Switch the unit back on with the main power switch. –1000 VDC +/- 5 VDC should be measured.

If the –1000 VDC is present; the symptoms listed in part 1 have other causes. Contact AA for advice

Bad Fuse on the High Voltage Power Supply Board.

• The next step is to put the MOA in standby position. Carefully pull the HV power supply from it’s slot and check the six fuses on the power supply with an OHM meter. Replace any bad fuses and carefully replace the HV supply and turn the unit back to ready.

24 VDC Power Supply for the HV Power Supply Interlock.

• Located on the lower front of the electronics bay is a large 18 screw terminal strip (TB1) located behind a clear plastic strip. Remove the plastic cover.
• With a voltmeter set to 50 VDC scale check voltage between pins 1 (24 VDC) and pin 2(ground). Pin 2 MUST be used for ground for this test. Chassis ground is not sufficient.
• 24 VDC +/- 1.50 volts should be present. If not then check fuses F4 and F5 on the fuse panel. Replace any bad fuses.
• If 24 VDC is still not present this indicates a bad PS5 24 VDC power supply. Contact Antares Analytical for a replacement.
• If the 24 VDC is present and fuses are good then please contact Antares Analytical for further advice.

For further information or access to past monthly Technical Bulletins covering a variety of subjects, please visit our website (under development) at www.antaresanalytical.com

For more information, to be added to this list,  or help with other subjects including Tech Support please contact us at info@antaresanalytical.com

To be removed from our monthly Technical Bulletin email list, please reply to this email with REMOVE in the subject heading and we will never bother you again, unless you request.

This email is not Spam and is intended to give Baird spectrometers users a better understanding of their Baird spectrometer and help them get best results from your spectrometer at the lowest reasonable cost. We would like very much your comments, suggestions for future articles and complaints. Antares Analytical needs you, the customer, to tell us how we can better service you.