EVB Kits have an automatic self-testing of the meter’s circuitry added to the microcontroller firmware, to simplify fault-finding if a newly-built meter doesn’t work properly.
What if it doesn’t work? In that case, the Meter’s firmware allows the microcontroller to do some basic testing of the electronics, to help you narrow down a problem to one area of the board. Before doing the self-test, it’s very important to first set VR1 to the centre of its adjustment range and make sure that the meter’s supply voltage is in the range of 8.5-9.5V.
Now switch the meter on by pressing and continuing to hold the button down, regardless of what the displays are showing. After five seconds, they’ll go blank for a moment, then show a test result for two seconds. The meter will then switch off by itself after you release the button. If everything is more or less OK, you’ll see “.8.8” on the displays (this shows that all the display segments and decimal point LEDs are working). However, if the microcontroller has detected a major problem, it will flash a fault code consisting of an “F” on the lefthand display and a character from 0-9 or an “A” on the righthand one.
Experience has shown that by far the most common cause of ESR meter kits not working properly is defective soldering. When a fault code directs you to a particular part of the circuit, carefully check (using a bright light and magnifier) for solder whiskers, non-soldered joints and track damage such as lifted solder pads. If you can’t see anything abnormal,
start checking for incorrect components and component placement errors such as transistors of the wrong type or with their leads in the wrong holes. If that doesn’t show up anything, you might have received a defective component in the kit,
though this is very rare. OK, here’s a list of what the fault codes indicate:
F0: Q11 is not discharging C10. Check around Q11 (BC338), R21 (10kΩ), R22 (470kΩ) and pin 4 of IC2 (Z86E0412).
F1: C10 is charging too quickly. Check that R22 really is 470kΩ and that R19 & R20 are 10kΩ. Make sure C10 is 470nF (0.47μF, code “474”). Check also for soldering and component placement problems around transistors Q9 & Q10 (BC558).
F2: C10 is charging too slowly (or not at all). Check around Q9, Q10 (BC558), R22 (470kΩ), R19 & R20 (10kΩ) and C10 470nF).
F3: Pulse amplifier output bias. <440mV (ie, at collector of Q8). Check R13 (100kΩ) & R14 (220kΩ) for correct values and check that D6 isn’t reversed. Check around Q7 (BC548), Q8 (BC558) and around pin 8 of IC2 plus associated components.
F4: Pulse amplifier output bias. >1V. Carry out the same checks as for “F3” code. Check also that D5 isn’t reversed.
F5: A test current source is permanently on. Check area around Q3, Q4 & Q5 (all BC328); R5, R7 & R9 (2.2kΩ); and pins
15, 16 & 17 of IC2.
F6: No output from pulse amplifier. This fault is usually due to the banana sockets being installed with +rt-circuiting them (see Fig.7). If that’s not the problem, check around C7 (33nF), R12 (1kΩ), D3 & D4 (1N4002), C5 (100nF) and C6 (47μF bipolar).
F7: Q3 not sourcing current. Check around Q3 (BC328), R5* (2.2kΩ), R6 (10kΩ) and pin 15 of IC2. F8: Q4 not sourcing current. Check around Q4 (BC328), R7* (2.2kΩ), R8 (1kΩ) and pin 16 of IC2. F9: Q5 not sourcing current. Check around Q5 (BC328), R9* (2.2kΩ), R10 (100Ω), IC2 pin 17.
FA: Q6 not switching on. Check around Q6 (BC338), R24 (10kΩ) and pin 1 of IC2. Obviously, the microcontroller can’t perform detailed tests on every component, so it’s possible that your meter is malfunctioning even though the self-testing hasn’t
shown up a problem. For example, if the meter is behaving strangely, “freezing” up or giving absurd readings on some values of test resistors, the most likely cause is a mix-up in the values of R6 (10kΩ), R8 (1kΩ) and R10 (100Ω). On the other hand, if the meter produces readings but there’s something wrong with the displayed characters, this is almost certainly due to one or more solder bridges between the pins of the large socket holding the displays, or around IC3. If the meter doesn’t stay switched
on when you push the button, check around Q2 (BC338), R3 (15kΩ), R29 (2.7kΩ) and pin 2 of IC2. If it switches off when you short the test leads, R2 (4.7kΩ) may be the incorrect value or Q1 (BC328) may have a low current gain. Finally, if you can’t get the meter into the test mode, zero it or switch it off, check for solder “whiskers” and open circuits around pin 3 of IC2, R4 (47kΩ) and D2.
Soldering How To..
http://www.youtube.com/watch?v=I_NU2ruzyc4
http://www.youtube.com/watch?v=3dkragEKSKI
http://www.talkingelectronics.com/projects/Soldering/Page1.html
