I was given a defective MD-4 Motor Drive for the Nikon F3.
The inserted accumulator pack had leaked and had corroded the contacts in the battery compartment.
I was able to clean that and the motor then worked with the alternative battery holder.
Anyway the battery check refused to work.
Two red LEDs are embedded on the back of the MD-4, next to them is a small push button.
If the battery voltage is sufficient, both LEDs light up as soon as you press the button.
But nothing happened here, the LEDs remained dark.
Research work
I worked my way through the service manual to understand how the battery check works.
A few sleepless nights also helped, then I got it:
There is a contact on a board next to the two contacts in the battery compartment.
If an accumulator pack is inserted, a small nipple on the pack presses in this contact.
The battery holder has no nipple, therefore the position of the contact remains unchanged.
In this way, the Motor Drive recognizes whether batteries with a higher voltage (accumulators) or batteries (AAA) with a lower voltage are inserted.
The contact in the battery compartment switches the voltage display so that it shows correctly in both cases.
Due to the visible corrosion on the contact, I assumed that it was not conducting and thus always signaled that an accumulator pack had been inserted. Since the battery voltage is lower, the battery monitor interprets this as empty batteries and the LED do not light up.
The leaked battery acid had probably spread to the back of the board with the connections for the battery pack and battery holder and corroded the contact.
To get there …
... I had to disassemble the MD-4
After loosening a series of screws mostly hidden under the leatherette, I could pull off the lower part of the case:
Here are the two LEDs with the push button on the left:
The board with the connections in the battery compartment is now accessible.
The arrow points to the contact for identifying the accumulator pack or battery holder:
Here is the back of the board.
The picture shows the dismantled plate from another MD-4 which I dissected for study purposes.
The arrow points to the contact:
I removed the contact.
You can see that it bridges a conductor track on the circuit board underneath.
On an accumulator pack the switch is open (no electrical connection) and on a battery holder it remains closed (electrical connection):
This picture reminds me of a colorful coral reef ;-)
The battery acid had raged, the contact is heavily corroded:
A bit pulling out and the solder joint the contact had been attached to broke. It just hung on its connection cable.
I suspected some corrosion damage, but I was surprised that it was that bad:
The contact was no longer usable.
I could have cleaned it and soldered it back in.
But to do that I would have had to remove the board and the mechanism behind it for the rewind function.
That seemed too risky for me.
This also eliminated the control for recognizing the inserted power supply (accumulators or batteries).
Since I only operate my motor drives with batteries anyway, I don't need this function and therefore not the contact.
So I permanently connected the gray connection cable to the underlying conductor track.
Here both they are already in place:
But how do I get cable and conductors together?
Soldering is not safe here, the location is too narrow for that. Collateral damage from heat would be expected.
Then I remembered two items I bought some time ago but had not yet used.
Self-adhesive copper conductor track and electrically conductive paste that acts like a solder joint after hardening, except that you don't need a soldering iron:
Perfect for this project!
I cleaned the spot from corrosion as best I could:
Through the opening for the contact on the board, I glued a piece of copper trace, which I applied to the conductor on the back of the board.
Unfortunately, this does not create an electrically conductive connection, since the adhesive on the copper track acts as an insulator.
So I had to connect the top of the copper trace to the conductor on the board.
This is where the paste came into play. That made the connection.
Arrows:
Red: copper track glued
Blue: Paste as an electrical connection between the copper track and the conductor on the circuit board
Green: conductor track
Here is the front of the board seen in the battery bay.
Where the contact used to be, the copper track is in position now:
I glued the gray connection cable with paste.
The motor drive now had to assume that the contact was closed and that a battery holder was therefore inserted.
The test
Yeah!
The battery control is working again!
The assembly of the MD-4 was also successful.
Function test passed on the F3/T.
The leatherette comes back in place later.
Mission accomplished!
***
Remarks:
After hardening on a piece of paper, the paste had a resistance value of between approx. 40 and 200 ohms at a distance of approx. three to seven millimetres.
Actually, a solder joint should be low-impedance, ie. less than 1 ohm.
I couldn't measure it in the motor drive, but I assume that this additional resistance reduces the luminosity of the LEDs and may indicate that the batteries are already exhausted, where this is not the case yet.
But that's not relevant, the battery indicator is only a helper.
In any case, a drop in engine performance cannot be ignored ;-)
The inserted accumulator pack had leaked and had corroded the contacts in the battery compartment.
I was able to clean that and the motor then worked with the alternative battery holder.
Anyway the battery check refused to work.
Two red LEDs are embedded on the back of the MD-4, next to them is a small push button.
If the battery voltage is sufficient, both LEDs light up as soon as you press the button.
But nothing happened here, the LEDs remained dark.
Research work
I worked my way through the service manual to understand how the battery check works.
A few sleepless nights also helped, then I got it:
There is a contact on a board next to the two contacts in the battery compartment.
If an accumulator pack is inserted, a small nipple on the pack presses in this contact.
The battery holder has no nipple, therefore the position of the contact remains unchanged.
In this way, the Motor Drive recognizes whether batteries with a higher voltage (accumulators) or batteries (AAA) with a lower voltage are inserted.
The contact in the battery compartment switches the voltage display so that it shows correctly in both cases.
Due to the visible corrosion on the contact, I assumed that it was not conducting and thus always signaled that an accumulator pack had been inserted. Since the battery voltage is lower, the battery monitor interprets this as empty batteries and the LED do not light up.
The leaked battery acid had probably spread to the back of the board with the connections for the battery pack and battery holder and corroded the contact.
To get there …
... I had to disassemble the MD-4
After loosening a series of screws mostly hidden under the leatherette, I could pull off the lower part of the case:
Here are the two LEDs with the push button on the left:
The board with the connections in the battery compartment is now accessible.
The arrow points to the contact for identifying the accumulator pack or battery holder:
Here is the back of the board.
The picture shows the dismantled plate from another MD-4 which I dissected for study purposes.
The arrow points to the contact:
I removed the contact.
You can see that it bridges a conductor track on the circuit board underneath.
On an accumulator pack the switch is open (no electrical connection) and on a battery holder it remains closed (electrical connection):
This picture reminds me of a colorful coral reef ;-)
The battery acid had raged, the contact is heavily corroded:
A bit pulling out and the solder joint the contact had been attached to broke. It just hung on its connection cable.
I suspected some corrosion damage, but I was surprised that it was that bad:
The contact was no longer usable.
I could have cleaned it and soldered it back in.
But to do that I would have had to remove the board and the mechanism behind it for the rewind function.
That seemed too risky for me.
This also eliminated the control for recognizing the inserted power supply (accumulators or batteries).
Since I only operate my motor drives with batteries anyway, I don't need this function and therefore not the contact.
So I permanently connected the gray connection cable to the underlying conductor track.
Here both they are already in place:
But how do I get cable and conductors together?
Soldering is not safe here, the location is too narrow for that. Collateral damage from heat would be expected.
Then I remembered two items I bought some time ago but had not yet used.
Self-adhesive copper conductor track and electrically conductive paste that acts like a solder joint after hardening, except that you don't need a soldering iron:
Perfect for this project!
I cleaned the spot from corrosion as best I could:
Through the opening for the contact on the board, I glued a piece of copper trace, which I applied to the conductor on the back of the board.
Unfortunately, this does not create an electrically conductive connection, since the adhesive on the copper track acts as an insulator.
So I had to connect the top of the copper trace to the conductor on the board.
This is where the paste came into play. That made the connection.
Arrows:
Red: copper track glued
Blue: Paste as an electrical connection between the copper track and the conductor on the circuit board
Green: conductor track
Here is the front of the board seen in the battery bay.
Where the contact used to be, the copper track is in position now:
I glued the gray connection cable with paste.
The motor drive now had to assume that the contact was closed and that a battery holder was therefore inserted.
The test
Yeah!
The battery control is working again!
The assembly of the MD-4 was also successful.
Function test passed on the F3/T.
The leatherette comes back in place later.
Mission accomplished!
***
Remarks:
After hardening on a piece of paper, the paste had a resistance value of between approx. 40 and 200 ohms at a distance of approx. three to seven millimetres.
Actually, a solder joint should be low-impedance, ie. less than 1 ohm.
I couldn't measure it in the motor drive, but I assume that this additional resistance reduces the luminosity of the LEDs and may indicate that the batteries are already exhausted, where this is not the case yet.
But that's not relevant, the battery indicator is only a helper.
In any case, a drop in engine performance cannot be ignored ;-)
