Someone who is familiar with this kit, would you lend some assistance?
I purchased and assembled the Mk.II version of Bob Parker's widely-praised ESR meter kit. Assembly went swimmingly.
The first test (with ICs removed) is to see what the power draw of the board is. It registered about 4.2 mA, whereas the instructions say that ~6.0 mA is typical. After installing the ICs and then doing the power-on diagnostic (holding the switch leads together), I get "F2" displayed on the LEDs. The instructions say that this means that there is a problem with the C10 cap charging too slowly, or not at all.
Following the clues of the troubleshooting section of the instructions, I've unsoldered the transistors Q9, Q10, and Q11 as well as C10. The transistors all check OK using my DMM in diode check mode (all junctions show approx.
0.6v bias in one direction only).I noted on first install that some of the transistors had some adhesive residue from the tape that held them in a roll (I presume they were purchased in a roll quantity). I ignored this on first install, but cleaned all of these transistor leads with contact cleaner before reinstalling them.
I checked C10 with my DMM in cap measure mode, and it is spot-on at 47 uF.
Likewise, I removed R19, R20, and R22, examined their resistance, and reinstalled them.
I can find nothing wrong with any of the components in this part of the circuit.
Both ICs have 5.02v at their power pin.
I've examined the solder job I did, many times, with several different power loupes; it's excellent. I've re-flowed all solder joints. I de-fluxed the board hoping that maybe the flux affected the circuit somehow. No joy.
I looked at some of the points in and around these components (Q9, Q10, Q11, C10, R19, R20, R22) using a scope, but I'm not sure what I should see. I looked at pin 4 of the u-processor: it transitions irregularly a few times a second. Is pin 4 the u-processor sense input of the charging cap? Should this voltage be a ramp (slow decay) of regular period?
To conclude I'll only add that I modified the board via Bob's follow-up instructions by replacing the 78L05 regulator with the micro-power, low-drop-out version (LP2950CZ-5.0) and changed R25 to 27K.
Some suggestions as to what I should see at certain pins, or where to look next would be greatly appreciated.
Thanks,