AR3000 / AR3000A memory modification
Firstly, do not attempt this modification unless you are experienced with electronics and know what you are doing. This modification describes how to add another 400 memory channels, 4 VFO's and 4 search banks to your AOR AR3000A.
If you study the circuit diagram of the AR3000A, you will notice the CPU has a 32K * 8bit static ram for storage of settings and memories etc. In the standard AR3000A, the first 16K of this memory is unused, so all my modification does is press this into service. Address line A14 of the uPD43256GU static ram chip is tied to +5v, allowing only the top 16K to be used by the CPU.
Looking at the picture below you can see the addition of a 10K chip resistor. The original +5v line to pin 1 of the uPD43256GU is cut, and this chip resistor soldered across the cut. A wire is then connected to pin 1. Using the spare switch cut out in the rear of the receiver case, you can fit a slide switch which will allow the required memory bank to be selected.
ONLY SWITCH BANKS WHEN YOU HAVE POWERED OFF THE RECEIVER
If you switch memory banks whilst the receiver is running, then you will experience erratic operation. Once you have performed this modification, you must switch to the new bank, i.e. wire shorted to ground, and press the reset button. This writes empty memories to most banks, and fills bank 1 with test frequencies. You should put at least 1 frequency in memory per bank, because if you switch between banks whilst in Memory mode, the receiver gets confused. I am not sure why this happens, as the entire bank of memory is paged with the new bank, so all settings etc are transferred.
Disassembly of the receiver is quite straight forward. Firstly, unplug the 13.8v power connection, antenna and any other connections to the rear panel. Place the receiver so the speaker grill is facing upwards, and remove the two screws by the front feet. Look at the back panel, and remove the 4 screws that hold the lower and upper halves of the case together. Carefully remove the bottom case as there is a connection for the loud speaker which you will need to unplug. Remove the upper half of the case. Place the receiver down and remove the tuning knob, along with volume and squelch knobs. Find the four screws that hold the plastic front panel on and remove them. Carefully pull the front panel off. In the keyboard switch matrix, you'll find a piece of plastic that looks like a small gate. hook this out and place with the rest of the casing.
Next, you have to remove the display / CPU board. Do this by removing the three screws either side of the front panel. Once you have done this, you'll have to prise the sides slightly whilst pulling the front chassis out. Be very careful, as the wires connecting the CPU to the radio are short.
Look at the photos below which shows in detail the modification.
On the back panel you will see there is provision for another slide switch, just above the computer control switch. Using a knife and file, remove the aluminium back cover from the hole. carefully drill out the two screw holes as well. Find a switch that fits and screw this in place.
Connect the centre pin of the slide switch to a suitable grounding point. I used a small piece of wire that runs back to the CPU board and is grounded there. Select one of the switched pins on the back of the switch and connect the wire that goes to pin 1 of the SRAM chip. I have the switch so in the down position it is bank 1 (i.e. normal factory bank) and the up position is bank 0.
Don't forget, you must perform the reset of the CPU after you have selected the new bank for the first time. If you do not do this, then you will see that many memories contain 0.000.0 as the frequency with a step size of 0. Whilst you have the lid off, you might like to replace the poor quality BNC antenna socket with a good quality N-Type socket. Other modifications you can perform include, adding a 10.7Mhz IF output, and putting a WX-Sat bandwidth IF filter in.
Reassemble the receiver and test. If all is well, you'll have 800 channels, 8 search banks, and 8 VFO's to play with.
(below) Original schematic
(below) Schematic with modification