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Many times the symptoms of a problem are very specific, leading you directly to the part of the tester at fault. If this is the case, you can skip this document altogether.

This document is intended for a situation where the symptoms are fairly broad, nothing seems to work. Or perhaps you have tried all the obvious things to no avail.

BACK TO BASICS is similar to the procedure we use in the shop to bring up a brand new tester. At this point we don’t know if anything works.

If some step in this process fails to work, you must find and fix that problem before going on. This assumes that you have an adequate supply of spares. If you don’t have the spares, you should at least call our shop before going on to the next step.

  1. The “bias supplies” should be turned OFF. That would be the red “OFF” button on the bottom chassis. Also if you have an FEC200, turn OFF the “2KV” switch near the left side of the TOP chassis.

  3. Temporarily turn OFF the operating power. That is the small toggle at the lower right hand corner of the TOP chassis.
  4. Now we will unplug many circuit boards while we test the core system. You can pull the boards out of their sockets but leave them in the slots where they belong. You will unplug most of the boards in the card rack, leaving only the B500 and the B501. Also from the back of the tester remove the four B502 station interface boards. While back there, check to make sure that the B621 computer interface board is firmly plugged in on both ends. Finally from the front, slide the relay chassis part way out and disconnect the 44-pin connector from the front of the relay board.
  5. Turn the operating supply back ON (lower right of TOP chassis).
  6. Restart the MAXX program. If it is already running, quit it, then restart it to make sure that the software is not corrupted.
  7. Check the +5V, +12V, and +/-15V supplies to make sure they are correct within 5%. To be extra sure, you might want to check them on one of the now empty slots in the card rack (having already checked on the banana jacks above). The +5V is on the top pins of the edge connectors (pins 1 and A). +15V is on 3 and C and -15V is on pins 4 and D.
  8. At this point you should see the normal MAXX screen display with NO red error message. If you have no error message, then the core Digital to Analog and Analog to Digital sub-system is working.

    If there is a SELFTEST error at this point the problem would have to be associated with the B500, B501, B621 or the associated cabling.


    You can retry to SELFTEST by entering the command SELFTEST. If the problem is still present it will just fail again but if the problem has been resolved or was transient the error message will go away. Turning off the power causes a SELFTEST failure, so you must always reset it after restoring the power.


    Some of the boards that are unplugged at this point share some logic lines with the B500 and B501 boards, so they could, if plugged in, cause a SELFTEST failure. However, let us leave them out for now and bring the tester up step by step.

    Be sure to check the +5V and +/-15V supplies each time after reinstalling a board to be sure the board is not pulling the supplies down.

  9. Next time we will get the handler interface up and running. Do this one station at a time starting with station 1. With the power OFF (as always when plugging in the boards) plug in the B502 for Station 1 and connect it to the manual test station. Note: The (4) B502 boards are identical except that each is jumpered for its own station number. So you can re-jumper a board from another station if necessary.

    Restore the power and enter SELFTEST (always enter SELFTEST after restoring power to make sure that the SELFTEST is still working).

    Now enter DIAG to get to the offline diagnostics and choose #9 “CHECK THE STATION/HANDLER INTERFACE” diagnostic. Choose PART 1. In addition to observing the bin lamps cycling, also press the “Start Test” buttons on the station to be sure that the EOT lamp goes out then back on.

    If these tests do not work, the problem would be with the B502 board (try another) or with the B621 computer interface. I am assuming here that the manual station itself is ok.

    If Station 1 does work add the other stations one by one. If you have a bad B502 you can still run the other three if you remove the bad board.

    Now re-connect the 44-pin connector to the relay board and restore power and SELFTEST to make sure that the relay board does not cause a SELFTEST error. If it does, the problem is likely a blown 74HCT374 chip on the relay board. It is connected to the bi-directional buss that drives the B500 board.

    If the SELFTEST is ok, that is all we want to know for this step.

  10. Next, we will try to do the Polarity and Kelvin contact check. This does not require any bias supply except the 12V that you checked earlier. Reinstall the B368 board and after power up and SELFTEST, you should note that the SELFTEST does not fail. If it does fail, then the B368 must be pulling down a logic line. You can now turn on the station with the manual station and TEST FOR POLARITY AND CONTACTS ONLY. You can use a completely blank test program since this test is hardwired.

    You can watch the colored blocks on the screen labeled SHORT, NP, etc. Try all possible combinations of the polarity, shorts, opens, and any of the four leads disconnected. (This will show CONTACT).

    If all of this works it checks out the B368 polarity board and also shows that the relay section is working at least to a degree. You should move the manual station to each of the (4) multiplex positions to be sure that all of the multiplex relays works.

    If these tests do not work, it could be the B368 board, the B621, or the relay board(s). You can narrow this down a bit by connecting the diode directly to the 6-pin connector on the front end of the B368 board. We have sent you an adaptor to make it easy to do this. Disconnect the 6-pin plug already on the board and substitute the test adaptor. Please be sure to put the original plug back when you are finished. This tests the B368 board while bypassing the relays.

    If the polarity test works at the B368 but not at the test station, the problem could be the relay board(s) but it could also be the B621 computer interface or a bad connection between the relay board and the test chips. Please be sure that these connections are good.

    Aside from the 74HCT374 chip mentioned earlier, the most common cause of relay board problems is stuck reeds. You can power down and carefully check the reeds with an Ohmmeter.

    In an FEC200, you must remove the top (B509) board to get full access to the B508 board below. This is not too difficult. There are just two screws on the rear panel holding this top board in place.

    Often stuck relays will release if they are shaken or otherwise disturbed so you need to treat them very gently when checking or the problem may (temporarily) go away.

    Another hint regarding the FEC200 relays. When you disconnect the B509 multiplexor board, you can still test a diode by connecting it directly to the jacks on the B508 board which are now exposed. This of course bypasses and thereby eliminates the B509 from consideration.

  11. If you have all of the above working, that is quite a lot, but you still have to check out the programmable test supplies and signal conditioning and scaling amplifiers. We will start with the IF supply (VF tests) and the 1.6V readout range.

    ****IMPORTANT NOTICE**** In the following tests we will be checking some signal conditioning and scaling amplifiers. There is another way to check these directly that is not covered here. The DIAG offline diagnostic program contains routines that allow you to test these amplifiers against an external voltage or current calibrator.

    You should reinstall load the operating supplies or cause a SELFTEST failure.

    If everything appears ok so far, turn on the RAW BIAS SUPPLY, that is the lowest chassis in the tester. Do all the LED lamps on the panel come on?

    You can use a DVM to check the voltages on the barrier strip on the back panel of this chassis. The following voltages are unregulated and the values given are approximate. The barrier strip is labeled with nominal voltages. The “20W” supply is also nominally 600V. The actual voltages may be a bit lower. Please also note that the “37V” supply is a floating supply that has no common with the other supplies.

    Try measuring a suitable diode at each of the following currents. Test the part(s) in other orientations. Do you get reasonable readings? Just reasonable, we can calibrate it later.

    TEST 1 VF 50MA 1V
    TEST 2 VF 500MA 1V
    TEST 3 VF 5A 1V

    If these things work, the B534 is at least functional on all ranges, the 1.6V range on the B501 is ok and the B400 is partially but not completely checked.

    If this doesn’t work it could be either of these (3) boards or our old friend the B621.

  12. Now the IR test up to 500V. First you must reinstall the B552 and B507 boards one at a time in that order. After each board is reinstalled, make sure there are no SELFTEST failures.

    If ok so far, than put an accurate 1M resistor in the test clips of the manual station and join the following program to that station and turn on WATCH.

    TEST 1 1 IR 1V 1µA T5000 F2

    Use a DVM to measure the voltage during the 5 second test. Read between common and the high side of the resistor (you can try both sides). Note both the voltage and your DVM and the reading on the screen at the end of the test. These should be 1V and 1µA, but don’t worry now about exact calibration.

    If the readings are approximately right go on and edit the test to change the voltage current as follows. Record each set of readings.

    10V 10µA
    100V 100µA
    500V 500µA

    If the voltage per your DVM is not right, the problem would be with the B507, B400, or the B621. You could also have a specific problem with the relay section although you have previously proved that the board is not completely dead by successfully doing Polarity and VF tests.

    If the voltage is ok but the current is wrong, then the B507 and B400 are ok but the B552 is suspect along with the B621 and the relays as above.

  13. Now VZ up to 500V. Use the same setup as in step 12 but start with the following test. In all of these tests read the voltage with your DVM and also read the voltage displayed on the screen at the end of each 5 second test.

    TEST 1 VZ 10µA 10V T5000

    The DVM volts will probably be ok since it depends on the same boards as step 12. The exception would likely be a very specific problem on the relay boards.

    If the tester voltage readout is wrong that would probably be the differential voltage amplifier on the B501 board. The B621 as usual could be bad or a specific relay problem. Even if the voltage is wrong, go ahead and edit the program to try the following values since they use different relays and a different readout board.

    100UA 100V
    450UA 450V

    The values readout through the B552 board. This board was partly checked out when doing the IR test, but to read voltage it must successfully switch in a series 1M resistor. It also depends on different logic outputs from the B621 board and different relays on the relay board.

  14. If you have an FEC200 tester the next step is to turn on and check the 2KV supply. We have kept it turned off until now because if it were out of control it could cause arcing which could in turn damage other components.

    Before turning the 2KV supply on we can check to be sure that the logic line from the B621 computer interface is telling it to be OFF. The 2KV supply is substantially contained on the B411 board contained in the top “operating supply” chassis. The logic line from the B621 that controls the 2KV on and off is a green wire jumpered to both pins 5 and 6 of the 15-pin “Molex” connector on the B411. That line should normally be at a TTL high level. If this is not true, don’t turn the supply on.

    If the control line is “high” you can turn on the “2KV” switch. You should make sure that the supply is not active. The voltage on the plate cap of the tube should be near zero and the voltage on the collectors of the (2) power transistors should be a steady DC voltage.

    If the supply appears to be active as indicated by a high pitched sound coming from the supply or by an approximately 3KHZ pulse on either of the (2) power transistors (on heat sinks), then don’t go on with the following tests until the problem is fixed.

    If the supply appears to be inactive (that is normal) then try the following test with a 1M resistor in the test clips.

    TEST 1 VBR 100µA 1KV

    The result should be reading of about 100V. If this does not work, the problem is probably the B411 board although it could be a bad output from the B621 board.

    Other possible causes could be approximately 16V unregulated supply for the collectors of the afore-mentioned power transistors. A very specific problem with the relay section could exist also. Remember that if we got this far successfully the relay section must be substantially ok.

    Also, please be sure that the cables from the operating supply to the rest of the tester are firmly plugged in.

    You can further check the 2KV supply with the following test using the 1M resistor.

    TEST 1 IR 1KV 1MA

    You should read about 1MA.

  15. This test although confirming that the 2KV supply will go to 2KV is mainly intended to check the reed relays (many of them) to be sure that they can stand 2KV (or a bit more) without breaking down. Remove the 1M resistor but jump the force to sense terminals together on each side of the test socket. Now use the following tests.

    TEST 1 VBR 100µA 2KV
    TEST 2 VBR 100µA 2KV F1

    Both tests should read a bit more than 2KV. They may vary a bit (not more than 100V) from time to time. The two tests check the relays for both NP and RP orientation. If the relays have low breakdown 1 or both of the readings will be steadily or intermittently significantly low. Don’t use the 2KV supply if this is happening. You will not only get bad readings but the arcing may damage other components in the tester.

    Note: A trim pot on the B411 sets the maximum voltage out of this supply. We normally set this to approximately 2100V.

  16. Finally we will reinstall the B530 board. This is used to readout the AC impedance tests only. This board as far as I know can only cause other problems in the set if it shorts out the power supplies. Otherwise it only controls the impedance tests. Try the following test with 1K Ohm in the test clips:

    TEST 1 EZT 1MA 10V <100MV

    You should read about 100MV. Then change the resistance to 100 Ohms and:

    TEST 1 EZT 1MA 10V 10MV <10MV

    You should then read about 10MV.

    If these tests fail, the problem is most likely with the B530, however, there is a small chance of trouble with the B621, B552, or B501.


If you have arrived here successfully your tester is probably working ok, although this document (by design) does not accurately calibrate the tester or prove every possible range or setting. As we said at the start, this is intended to deal with a major problem with multiple or confusing symptoms. It will get the tester back to functioning overall. You should then do a complete calibration, which may show up other more subtle problems.

By the way, did you notice how many times I wrote “B621" in this piece? We don’t have all that much trouble with the B621 (although we have had some). However, the B621 controls the complete interface between the tester and the computer, so it can affect just about all the functions of the tester.

The B621 board is used in testers built in 2003 and later. It replaces the B499 used in older testers. These boards are not interchangeable even though they perform the same functions.

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Last Updated September 12, 2007
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