Localizing the Problem to PCB level
The key to successful troubleshooting is to localize the problem to a general electronic parameter (i.e. current
source or DVM PCB) as much as possible. Certain questions should be asked such as "Does the problem occur
on all ranges or on a specific range only?". If the 620UK Ohmmeter does not come on when powered up, did
you check the power switch.
PCB Exchange/Replacement
If the malfunction is a faulty component, the repair of the AMPTEC 620UK Ohmmeter can be maintained by
replacing the proper internal PCB (Printed Circuit Board) that the faulty component is located on. AMPTEC
620UK Ohmmeter PCBs use ribbon cables with easy to disconnect connectors. There are no serviceable or
faulty component replacements necessary on the 620UK PCBs, it is a case of PCB replacement. AMPTEC
provides a “No-Charge” PCB replacement while the 620UK Ohmmeter is under warranty (1 year) and a small
charge for “non-warranty” repairs.
Use only the specified component or its exact equivalent. Spare replacement PCBs can be ordered from your
nearest AMPTEC RESEARCH Service Center or directly from the factory by referring to the AMPTEC Stock
Number listed in the Parts Lists section at the back of this manual.
A-6 Trouble-shooting or Diagnostic Test Procedure for AMPTEC 620UK Ohmmeter Printed Circuit
Board
(diagnosis or replacement)
The following steps will facilitate the proper repair personnel to diagnose whether the AMPTEC 620UK
Ohmmeter
Current Source PCB
or the
Digital Voltmeter PCB
needs replacement.
A-6.1 Current Source PCB Diagnostic Routine (bottom internal PCB)
* Place the AMPTEC 620UK Ohmmeter in the 20 Ohm range.
* Put output leads across a 10 Ohm resistance standard (0.005% or better).
* Measure the voltage drop with a DC Voltmeter, it should be 0.05V .
* Place the AMPTEC 620UK Ohmmeter in the 200 Ohm range.
* Measure the voltage drop with a DC Voltmeter, it should be 0.005V.
If any of these tests are not true then the Current Source PCB is faulty and needs replacing.
A-7 PCB replacement Procedure -
Use caution when pulling the PCB from the aluminum case, as there is umbilical wiring and ribbon cabling
that connects the front panel electronics to circuitry mounted inside the 620UK case. Slide boards out to gain
access to the main PCB.
Use the snake eye screwdriver (option “620UK-201) to remove the Ohmmeter’s 4 front panel screws. located
in the corners.
* Pull the front panel forward and carefully slide out the two PCB's.
* Disconnect all wires and cables that go to the bad PCB.
* Reinstall all wires and cables on to the new PCB.
* Follow the calibration procedure (below).
* Slide the two PCB's back in and replace the front panel and screws.
18
