KIT FAULTS
& MODIFICATIONS
CURRENT
KIT VERSIONS:
OLDER KIT VERSIONS:
CURRENT
EME85F KIT VERSION
These
are EME85 Kits since 2002 with board letters EME85D, E, & F
that have the plated through holes. All these Kits were supplied
with Version 2.10 software & used the PIC16F628 & AD9851
chips.
1/ Any
problems associated with the PIC16F628 chip can normally be confirmed
by checking that it lights up the LCD display correctly, & that
the control board works correctly. This however will not test the
data & clock signals to the DDS chip that can be confirmed with
an oscilloscope. Most problems with the LCD not lighting up are
due to wiring errors & not the DDS chip. The DDS chip will not
prevent the PIC16F628 from working the LCD display
2/ If you have problems with
the LCD not lighting up, or the control board not working &
want to confirm if the DDS board is ok, then the EME85 board can
be tested by disconnecting the LCD & control board connections
& turning on the DDS. The PIC16F628 supplied with Kits
is programmed for a 10.5MHz output that can be checked on a suitable
HF receiver. This is only the case if you are using a 30MHz
xtal module & the menu settings have not been changed.
3/ Some pins around the AD9851
chip may appear to be shorted with solder. This is quite ok as the
pins are all ground connections & are connected underneath the
chip. If you have problems with the DDS chip not producing any output
then please check for unsolderd pins.
4/ When using the DDS as a local
oscillator for a receiver or transmitter, a simple one to one PLL,
( phase locked loop ) circuit with VCO, ( voltage controlled oscillator
) may be required. The DDS used on its own may produce an
approximate 1Khz audio tone to be heard from the receivers speaker.
This is due to the DDS output being rather complex with the frequencies
that are produced. Most modern Transceivers that use
a DDS, use one as a reference oscillator on a PLL. A simple
1MHz high pass, or bandpass filter on the output of the DDS may
fix this problem.
5/ A MAR-6 now replaces the ERA-5 in new
Kits. It has better low frequency gain compared to the ERA-5
& is much lower cost. The Standard bias on the MAR-6 is
normally 16mA which would give us gain compression due to being
overdriven by the AD9850/51 output. If we raise the bias the
MAR-6 to 30mA using a 270ohm resistor, we raise the P1db from +3dBm
to +10dBm output which is still under the maximum recommended 50mA.
Thanks to Lim Chin-Leong 9W2LC for this idea.
All later Kits are fitted with the MAR6 & 270ohm resistor.
6/ There has been a report of thecalibration menu settings not
being able to be set. Please disconnect the 4 x 3 Keypad & see
if the menu works ok. A faulty keypad with leakage was found to
have caused the fault.
OLDER
EME85 KIT VERSIONS
These
are the older EME85 Kits 2001 or older with board letters EME85,
A, B & C. All these Kits were supplied with Version 1.50 software
or older & used the PIC16F84 & AD9850 chips. These board
also had no plated holes or solder mask greatly increasing the possibility
of construction faults.
1/ If you are using a AD9850 chip you need
to program the PIC with the DDS_9850.HEX file contained in the dd_synth_v21
ZIP software file. The menu setting to set for either a AD9850 or
51 chip was disabled in Version 2.10. This was to fix the unexpected
problem of possibly destroying an AD9850 chip if you have set the
PIC software for a x6 multiplier which the 9850 does not have.
2/ If
you have one of the older Kits with software versions 1.50 or older,
then it is best to upgrade the software & use the later EME129
control board kit. We are no longer supporting the older software
versions so any problems associated with the older software are
no longer listed on the web site.
3/ One fault
that has been reported for this Kit is low output from the clock
module, causing erratic frequency jumping. The problem seems to
be the output from the clock module being low, & can be fixed
by biasing the clock input pin9 of the AD9850 to 2.5v. Refer to
the diagram
for modification. Thanks to Kam Ng for this one. Another remedy
for this could be to change to a different brand of clock module.
One brand was found to not quite reach 0v on the low clock cycle.
4/ Erratic Frequency
jumping when tuning was found to be a crook PIC16F84 microprocessor.
Reprogramming the PIC did not fix the problem, it had to be replaced.
5/ Low
output from the ERA5 amplifier could be due to the 150ohm resistors
leg on the ERA side being soldered to the bottom earth of the PC
Board. This pad should be recessed on the ground plane side, or
the leg of the resistor should only be soldered to the top track
side of the board.
6/ For
any other problems, check that there is no copper tracking between
tracks on the PC board. This has been a common problem around
the AD9850 chip.
7/ For incorrect output frequency compared
to what the LCD display says, Please go to the CAL menu
first & check the settings for the Xtal Oscillator Module that
you are using.
8/ For no or
low +5 volts on the AD9850/51 DDS IC check that the +ve connection
on the 10uF capacitor on the output of the 7805T regulator, is soldered
on both sides of the board. The connection is a feedthrough
from one side of the board to the other.
Thursday 7th August 08 
