FETAudio FDA-2A Manual - page 8
FDA-2A Manual.doc
Rev. 1.0
Page 8
31-Aug-2012
D. Tuning and Testing Procedures:
1. With all the parts in place except the 3 wires, L8 and L15, insert the NOS daughter board
in place (U18).
2. Connect AC 9V (or a regulated power supply with current limit set to 200mA at 12Vdc)
to J55 (do not connect J58 and J59 to AC 18V), check the voltages at U1 big pad (5V), U6
and U7 (LM317T) metal body (not the big heat-sink that it attached to) relative to
ground (DGND at U18 daughter board). The voltage at all 3 locations should be at about
5V +/- 0.1Vdc. If the voltage is outside the range, cut off the power immediately and
check for wrong component used or open/short soldering.
3.
Solder L8 and L15 if the regulated voltage at U1 and U6 are at 5V.
4. Then check the voltage at U8, U10, & U17 (AMS1117-3.3). The voltage at the little heat-
sink of the regulators should be 3.3V +/- 0.1Vdc.
5. Plug in the Front Panel Control Board (V7.1) via J1 on both PCBs using the 10-pin flex
cable provided. D1 (USB/I2S) and D5 (if set to Power LED) should be “ON”. Press the
toggle switch (at J2 or J14) to see if the LEDs D1 to D4 is “ON” one by one. The sequence
is from D1 D4 D3 D2 D1 D4 … and repeat.
6. Inject a digital SPDIF1 signal to J4 (lower RCA socket), the LOCK LED (D6) should be “ON”
if SPDIF (D4) is selected. This shows that the digital section is locking to input signals.
7. Then remove the power at J55.
8. Connect AC18V (or a regulated power supply with current limit set to 300mA at 24Vdc)
to J59, check for voltage at J21 for -20V to G points. The initial voltage should be around
-15.5V to -16V. Adjust VR8 until the voltage is -20V +/- 0.02Vdc. Remove the power
applied to J59.
9. Connect AC18V (or a regulated power supply with current limit set to 300mA at 24Vdc)
to J58, check at J21 for +20V to G points. The initial voltage should be around 15.5V to
16V. Adjust VR7 until the voltage is +20V +/- 0.02Vdc. Remove the power applied to J58.
10.
Solder the 3 wires provided from J19 to J21 at the bottom of PCB.
Make sure that the
wires are connected from -20V to -20V, G to G and +20V to +20V points.
11. Connect power to all J55, J59 and J58.
Check the +20V and -20V are still at about the same voltages as before. If not, the IV
section is not work properly. Cut the power immediately and do trouble shooting. The
common mistake is transistor orientation wrongly mounted on the heat-sink.
12. Output DC offset adjustment:
13. Check the offset voltage at C246 (C83) inner hole relative to Ground (G point of J14). It
should be around -0.45Vdc. Adjust VR1 until this voltage to below +/-1mVdc. Repeat at
C247 (C84) and adjust VR2 to within +/-1mVdc offset.
14. After warm up for 30 minutes, repeat above steps 11 to 13 to ensure the offset is below
1mV by adjustment again if necessary. For normal use, the offset of +/-5mV is ok as all
output has couple capacitor to block any DC from going to the output sockets.
15. Re-adjust +20V and -20V regulated voltages if necessary
16. Check the DAC AD1955 analogy pins DC offset voltage at two sides of C56 and C67
(100pf SMD capacitors). The DC voltage relative to DGND should be at about 2.7xV
(close to 2.8V).
17. Check the VREF voltage of AD1955 at the J17 “Square” pad. The voltage should be close
to 2.39Vdc.
18. If all the DC adjustments and check are done, proceed to AC measurements below.
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