Self-Service Guide for EISAIX32-A

The Bus Isolation extender basically isolates the power and the signals from the motherboard to the I/O boards under test. It serves two purposes, one is to protect the motherboard from being damaged and the other is to allow repeated board test without having to power the whole system up and down. However, the user I/O board under test should be inserted or removed from the extender only while the extender is switched off. The extender could be switched on and off by either the toggle switch on the extender or by external TTL signal issued from external sources under software control.

The bus isolation extender itself, should be secured firmly onto the motherboard in either open or in-chassis test environment. This will prevent it from being accidentally lifted while the system power is still on. If this happens, the extender and the motherboard will be severely damaged.


  1. Check all fuses for continuity.
  2. Check all isolated and non-isolated power short to ground.
  3. Check all isolated and non-isolated power short to +5V.
  4. Check all isolated and non-isolated power short to isolated 5V.
  5. Measure the resistance between the isolated power to ground which should be about:
    ~ 2K ohm for isolated +12V (Pin B09, F09, White)
    ~ 2K ohm for isolated -12V (Pin B07, Blue)
    ~ 300 ohm for isolated +5V (Pin B03 and etc., Red)
    ~ 300 ohm for isolated -5V (Pin B05, Yellow)
  6. If the resistance are not correct, then either the related TVS or the Resistors are damaged. Replace them and try again.
  7. Switch Isolation Extender off.
  8. Insert EISAIX32 into tester system, with tester system power off.


  1. With isolated switch off, check all isolated voltages (should all be near zero).
  2. Check bias voltages, they should be,
    ~ +0.3V at Q4.1
    ~ +11.7V at Q3.3
    ~ -11.7V at Q2.3
    ~ -5V at Q1.3
  3. Switch Extender on, Red LED should be flashing.
  4. Check all Isolated voltages, they should now follow the non-isolated voltage.
  5. Check Bias voltage again, they should be,
    ~ +12V at Q4.1
    ~ 0V at Q3.3
    ~ 0V at Q2.3
    ~ +12V at Q1.3

If any of the above conditions are not correct, then the power control biasing components are damaged. Verify the switch operation, and then try to change the related components according to the schematic. If still not correctable, then contact us with symptoms for further assistance. Please read the user manual for detail board operation. If the above conditions are correct then proceed to check the buffers.


A simple way is described in the following text to check out the buffer ICs without having to power up the extender board. Even though this is not a fool-proof method, it will capture most of the damaged buffer ICs.

  1. Select a Digital multimeter that does not put out more than 6.0V when set to 20M ohm range (verify it with another DMM), such as Tektronix DMM Model 155.
  2. Place the Positive probe on the VCC pin of the buffer IC (pin 20).
  3. Place the Negative probe on the signal pins of the buffer IC (pin 2 ~ 9 and 11~18).

    The DMM should read a very high resistance, approximately 12M to 15M ohm (The reading may be different depending on the type of DMM used).
  4. The reading should be fairly consistent within each package. If any of the pins have a much smaller or much larger reading , then the IC should be replaced.
  5. Repeat this test again with the positive probe on the ground pin (pin 10).

We strongly suggest you replace any of the buffer ICs that have visible physical cracks or do not have the right reading, and then try the extender in your system again. If the extender still fails, we suggest you change the rest of the buffer ICs. This will save you time for further troubleshooting. One could also use logic probe or scope to check the buffers. The signal on one side should travel to the other side, when the buffers are turned on. If not, replace the buffers. Note: Not all signals are active at all times, during any particular bus cycle.

Usually the buffers at the corners, on both sides, are most likely to be damaged. This happens, when user forgets to turn off the extender while removing the user I/O boards. This is due to voltage pins being close to the buffer pins near the corners and when pulling the board up, the voltage gold fingers touch the buffer pins on the extender connector.

The isolation buffer ICs are very sensitive CMOS analog switches. Sparking or over current are usually the major causes that damage the buffers. When these buffers are damaged, they may short to VCC, Gnd, and become very resistive or overheat. We strongly suggest you be aware of ESD and handle the extender with care.

Please see the EISAIX32-A parts list and QS3245 pin out for buffer pairs. Update your board with the component values on the parts list if necessary.

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(C) Copyright 1998, Adex Electronics, Inc. 3 Watson, Irvine, CA 92618, USA. (T) 949-597-1772; (F) 949-597-1729
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