Self-Service Guide for AGPIX32-D

The Bus Isolation extender basically isolates the power and the signals from the motherboard to the I/O boards under test (UUT). 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.

The AGPIX32-D and the AGPROIX-B share the same printed circuit board. The only difference is the connector on the top and the keys being cut around the gold finger area.

1. Read the AGP specification (version 2.0), to understand the gold finger pin out, A side (solder side), B side (component side), VDDq (1.5V for 4X; 3.3V for 1X,2X), gold finger key cut definitions and etc. Some information is also available on the FAQ section of Adex's web pages.

2. Read the AGPIX32-D user's manual for proper understanding of the theory of operation. Be familiar with the location of jumpers, MOSFETs, buffer ICs, switch operation, buzzer and LED operations, and etc.

Static Check (without applying power to the AGPIX32-D

  1. Check all fuses for continuity and proper value as listed in the user's manual.
  2. Check all isolated and non-isolated power short to ground.
  3. Check all isolated and non-isolated power short to +5V.
  4. Measure the resistance between the isolated power to ground for the following voltages, with positive meter probe on the voltage pins and the negative meter probe on a Ground pin (e.g.. B5 or A5 of the connector), the value should read about:
    ~ 30K ohm for isolated +12V (Pin A1 of the connector)
    ~ 12.9K ohm for isolated 5V (Pin B2 of the connector)
    ~ High resistance (in mega ohms) and drifting for isolated 3.3V (Pin B9 of the connector)
    ~ High resistance (in mega ohms) and drifting for isolated VDDq (Pin B64 of the connector)
  5. If the resistance are not correct, then the related resistors or capacitors are damaged. Contact Adex for detail.

Dynamic Check (with power on, but without UUT on top of the extender):

  1. Place the AGPIX32 into the system chassis (platform), switch off the on-board toggle switch and then power up the system.
  2. The green LED at L7 (VCC), should come on.
  3. With the toggle switch off (down position), check and verify all isolated voltages, all should all be near zero.
  4. Check bias voltages, they should be,
    ~ 0.45V at Q1.4 (bias for 5V N-MOSFET)
    ~ 11.7V at Q2.4 and Q3.4 (bias for 12V P-MOSFET)
    ~ 0.45V at Q4.4 and Q5.4 (bias for 3.3V N-MOSFET)
    ~ -0.45V at Q6.4 (bias for VDDq N-MOSFET)
  5. Switch the extender on, by toggle the switch to up position
  6. The Red LED at D1 should be flashing, and the buzzer should buzz about once per second (if jumper at W11 is in)
  7. Check all Isolated voltages, they should now, follow the non-isolated voltages.
  8. Check Bias voltage again, they should be,
    ~ 12V at Q1.4
    ~ 0V at Q2.4 and Q3.4
    ~ 12V at Q4.4 and Q5.4
    ~ 12V at Q6.4
    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 following:

    R9 (15K), R6 (430) and C4 (1uf) are used for the biasing of the Q1 ( 5V).
    R11 (820), R12 (43K) and C3 (1uf) are used for the biasing of the Q2 and Q3 (12V).
    R7 (420), R10 (22K) and C2 (1uf) are used for the biasing of the Q4, Q5 (3.3V) and Q6 (VDDq)

    If still not correctable, then contact Adex with symptoms for further assistance.

  9. Switch the extender off, place the UUT on top of the extender, and then switch the extender back on. Verify the biasing voltage and the isolated voltage. If excess voltage drop appears, then replace the fuse (eventhough it is good under static check), and try again.

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 or better.
  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 (pin 1 and pin 10 are grounded).

    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 may be damaged. However, there are exceptions, please check with the following, before replacing the buffer ICs.
  5. Exceptions 1:U10 pin 3,5,15,17; U5 pin 3,17; U7 pin 8,12; U9 pin 5,7,13,15; U12 pin 8,12; U14 pin 3,17and U16 pin 6,14 should all read zero (grounded pins).
  6. Exceptions 2: pin 19 of all buffer ICs should read about 4.7K ohm.
  7. Repeat this test again with the positive probe on the ground pin (pin 10 of the buffer IC) and negative probe on the signal pins. The resistance reading will be different from the above step, but should be consistent. If in double, compare the reading with other known good boards.

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. 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 (except the pins that should read zero). If not, replace the buffers. Please see the buffer pinout below for the input/output signal pair. 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. There are voltage pins close to the signal pins, near the corners, and when pulling the board up, the I/O board gold finger may short them out, causing damages to the corner buffers, if extender is not switched off. .

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 AGPIX32-D parts list and the QS3245 pin out for buffer pairs. Update your board with the component values on the parts list if necessary. User can download the AGPIX32-D user manual, AGPIX32DMAN.PDF, in pdf format . The file size is about 1,498Kbyte.

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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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