The boards below have been used over the years in FEC100 and FEC200 testers. These boards affect the accuracy of the readings, hence the term “Calibrated Boards”. Of course some other boards may affect the readings if they fail but are not calibrated in the usual sense. The boards are listed in the order that they appear in the card rack viewed from the front and starting on the right. The most recent versions of the boards are listed, but where they replace, pin for pin, those earlier boards are described also.
- B500 The B500 is a dual 14 bit Digital to Analog converter (DAC). It is central to the accuracy of the testers since it is used in all analog tests. It is the most precise board in the tester. Fortunately it is also very stable and reliable. Further it is easy, using a precision DVM to test the board in the field. If you follow the instructions at the end of this document to check the B500 you can determine if it needs to be sent for calibration. The B500 is used in most FEC testers and unless there is a label on it indicating otherwise, it is interchangeable from tester to tester. But be sure to run the procedure mentioned above!
- B501 The “standard” versions of both the FEC100 and FEC200 use the “standard” version of the B501 which has two differential voltage scales of 1.6383V and 16.383V. It is also a board which, is critical to the accuracy of almost all tests, but especially critical for readings of low voltage (<16V) zeners. THIS POSITION HAS SEVERAL VARIATIONS. Some of our customers asked to change the 16.383V scale to 24.574V. A version of the B501 exists with that scale. A jumper on the B499 (or B621) interface board informs the MAXX software if this board is used. Please be careful! If the board and jumper do not agree then the low voltage VZ readings may read either two thirds or 1.5 times the correct value.
For testers (either FEC100 or FEC200) that are converted to test Thyristors, the B501 is replaced with a B522. The B522 performs similar functions but also has a “Peak Voltage” capability, as well as different differential voltage scales. It too, requires a jumper to inform MAXX of this change. There are a few variations on the B522 which make it important to avoid swapping boards between testers. Please check with FEC if in doubt about interchangeability.
- B552 The B552 (or B478) measures IR or VBR/VZ at higher voltage readings than the scales on the B501. It is also used on impedance tests such as ZZT/ZZK or ZT/ZK. Both boards are interchangeable (with qualifications). The B552 board although providing the same scales as the B478 is improved sufficiently in accuracy and stability that we do recommend upgrading as the budget permits. The B552 also incorporates a 100mA over-current limiter for IR tests. This is nice to have but is not crucial in most cases. Some VERY early B478 boards did not have the 10nA IR scale that all B552 and most B478 boards have. We hope that all such B478 boards have been retired but advise that you check if you have some very old testers.
- B530 The B530 is used exclusively to measure the AC voltage or current for impedance tests. It replaces the earlier B391. Like the B552/B478, the boards are interchangeable BUT, we do recommend upgrading to the B530 as the budget permits. If you don’t measure “impedance” tests on a given tester then it doesn’t matter since the board is not used in that case.
- B400 The B400 is a critical board. It provides the reference for programming both voltage for IR tests and current for all constant current tests up to 4mA. All B400 boards are interchangeable (unless labels say otherwise). However we have improved the B400 over the years and we do upgrade any B400 boards returned for calibration or repair.
- B534The B534 board replaces the earlier B443 and they are interchangeable with similar qualifications. Further, the B534 may be slightly modified if used in a “thyristor tester” The change does not effect “normal” tests but is required to test thyristors properly. The B534 (or B443) board provides constant current biasing for VZ/VBR and for VF and other “Forward” tests. The scales are 0 to 40.00mA, 400.0mA, 4.000A, and 40.00A.
- B507 The B507 board provides biasing, both constant voltage and constant current for “Reverse” tests up to 500V. The only qualification regarding interchangeability relates to thyristors. All reasonably modern boards can measure thyristors but there may be some old boards out there that need minor changes for thyristors.
- B411 The B411 (not in the card rack, but in the top chassis) provides biasing for tests that need more than 500V. It seldom (if ever) needs to be calibrated. It may fail causing noticeable errors on high voltage tests but that is more of a repair than calibration. There are two versions of the B411 that are very different in form factor. You can’t mistake the difference. If it fits you can use it. Most B411 boards are used with a (shudder) vacuum tube. These tubes have a “wearout” mode of failure where they cannot pull the output voltage LOW enough. We have recently designed a solid state replacement for the tube that does not exhibit this failure mode. A very minor change to the B411 board is required to use the solid state “tube”.
- ABOUT THYRISTORS. As you can note from the above, several boards (where noted) may have minor modifications where used to measure thyristors. There were some wiring changes in the tester also. All wiring of new testers and most (but not all) board changes were incorporated in future testers after we started testing thyristors. When testing thyristors, if in doubt, please check with us.
- B500 FIELD CALIBRATION CHECK The DIAG (DIAGNOSTIC) utilities included in MAXX can check the B500 board pretty thoroughly against an external DVM and also against some other internals. Enter the command DIAG and follow the on-screen instructions. If you have questions or need help please contact us. IMPORTANT NOTE: The DVM that you use should be very accurate. The B500 is typically more accurate than inexpensive portable service type DVMs. We use an HP34401A, which is sufficiently accurate for the purpose. NOTE: The B500 and B501 (or B522) working together provide the basic Digital to Analog and Analog to Digital sub-system that all other analog tests use. The diagnostics included in MAXX together with an accurate external DVM allow the user to check this vital sub-system fairly thoroughly.
- RESISTORS ON RELAY BOARD There are some precision resistors on the B508 relay board in the FEC200 and the B503 in the FEC100. These 1M or 10M resistors affect the accuracy of programmed voltage or VBR readings on scales higher than the B501 or B522 boards provide. It is extremely rare to have these resistors fail but it is important not to forget them. Also, note that each resistor consists of several lower value resistors in series. The stability of the resistors used has always been good but the more recent ones are even better. Measuring the 10M resistors with a DVM must be done with great care (if at all). A shunt across the resistor causing a 0.1% error would be 10G Ohms. Holding the test leads in your hands could cause such an error!
FINALLY If you measure IR at very low levels and especially at high voltage, then leakage or dielectric absorption on relay boards, or test fixtures may cause IR to read high. If trouble-shooting such an issue, try making the test very long (seconds) to eliminate the dielectric absorption as the cause. Also check to see that the leakage is not in the test fixture. Sometimes we find relay boards that have been contaminated in some way may have high leakage. In such cases we clean and thoroughly dry the boards to eliminate the leakage.