On February 6th 2005, I decided to change the back-up battery in one of the mk1 DX7's. I haven't done this before, so I opted to try the following method out on my 'worst' mk1 - it has MIDI problems (UPDATE 2007 I have since discovered that these MIDI 'problems' are in fact normal behaviour of very early DX7's up to serial number 26005).
I didn't actually need to change the battery - the 'Battery Check' was still showing 2.8V, and there was no sign of leakage or memory loss. But I think this was the original CR2032, judging by what appeared to be a date stamp of '83, and I didn't want to wait around for it to start leaking.
The correct way to change the battery involves dismantling many parts of the DX7 such as the side panels, keyboard etc in order to gain access to the underside of the motherboard. This should always be done by a trained technician. As I have an amount of electrical experience, I decided not to do this; instead I wanted to try from above, without pulling the thing apart.
Important: I am not giving instructions as to how to change the internal battery, as I am not qualified to do so. This should always be carried out by a trained technician or someone who can competently work on circuit boards. I have merely documented how I managed to change the back-up battery myself.
The back-up battery is a CR2032. These are widely available and can be bought very cheaply on Ebay. I decided I would install a battery holder as well (from RS), to make future changes easy ( the battery can be simply lifted out and replaced).
After making sure I'd backed up the sounds, and making sure the DX7 was unplugged from the mains, it was time to delve inside.
I removed the top-panel screws. Opening the lid exposes the electronics - The power supply / transformer etc are on the right, and the motherboard is on the left.
The battery is located roughly in the middle of the DX7, so this makes it easy to get to...
...but because it's soldered in place, it's not so easy to take out !!
This 20+ year old battery was soldered on two 'legs'. I realised it may be possible to get the battery out from above.
I carefully prised the +ve terminal away from the battery, taking care not to exert too much force against where it connects to the circuit board...
...this gave me access to the -ve side of the battery...
...allowing me to also prise this terminal away from the battery.
This left the two exposed terminals, easily accessible (note the polarity symbols printed on the circuit board).
I carefully soldered two 15cm (6") lengths of wire, colour coded for reference. UPDATE 2007: I have since reduced the length of the wires to around 5cm, as I found the battery was draining quicker than expected - probably due to resistance in the wires.
I then insulated the terminals with insulating tape, to help reduce accidental contact against other wires, if they ever come loose. The other end of these wires go to the new battery holder (below).
After soldering the wires to the battery holder, observing polarity, I put some more insulating tape around the terminals on the holder, simply popped in a brand new CR2032, and stuck it to the back-panel with Velcro. UPDATE 2007 - I have since covered the whole battery in insulating tape, as I was concerned that exposed 'metal' could create a 'short' if it ever comes loose.
Job done!!...nearly...
When I switched the DX7 on, as expected, all the internal sounds were lost. The LCD displayed a lot of garbage for the Voice names. Also, the parameters in the Function menu were all over the place ( e.g. the display said the DX was set to MIDI channel 43 !). The portamento was set to a high value, resulting in a long 'slide' up and down the keyboard. That was no problem; I just went into each function and 'moved' the data slider up and down, to get 'proper' readings for each setting.
I am pleased to say that after loading my sounds back in with Midilib, the DX7 is working fine, with a healthy 3.0v on the Battery Test page ! Next time ( in about 2027 !! ) I'll be able to simply lift the old battery out and put a new one in, without going anywhere near a soldering iron!
I have now carried out this procedure on four DX7 mark 1's, successfully. I haven't tried it yet on my DX7IIFD, but will photograph and post my attempt when I do later this year.
