Repairing a K2000R synthesizer: battery backed memory

[Robert Graham Jr.]

Hello all!

I am repairing my K2000R synthesizer. When I turn the unit on, it states it
is initializing battery backed memory. But the batteries are fine. Still, I
do get a low voltage indication at times. At first this was an intermittent
problem. Now it is a consistent headache.

I replaced the diode pair that permits the battery to power the memory chip
when the power is off. There is also a transistor that I changed which a
part of this circuit. It brings the +5V power line up when unit is switched
on and cuts off power from the battery. There is a capacitor that permits
changing the battery without losing what is in memory. Also there are the
memory chips, the battery sensing chip, and the battery pack of three AA
1.5V batteries. Oh yes, there is the cable that attaches the battery pack
to the board.

I removed the battery pack container and measured the voltage across the
external terminals with NEW batteries installed. Even though each battery
measured 1.5V separately, I measured 3.7V across the terminals with the
three AA batteries inserted. This slowly dropped to 3.3V. Interesting.
Particularly when the battery pack is not connected to the board! I then
plug in the battery pack into the board and after the battery reading
stabilizes (the capacitor is charged), the voltage reads under 2V. I unplug
it, and the battery voltage jumps to 4V. I think there is a connection
problem here. Otherwise this is not making any sense to me.

Any ideas? I am teaching myself how to repair this problem. I appreciate any
help!

Thank you!

Bob Graham

 

[Bob Urz]

Hello all!

I am repairing my K2000R synthesizer. When I turn the unit on, it states it
is initializing battery backed memory. But the batteries are fine. Still, I
do get a low voltage indication at times. At first this was an intermittent
problem. Now it is a consistent headache.

I replaced the diode pair that permits the battery to power the memory chip
when the power is off. There is also a transistor that I changed which a
part of this circuit. It brings the +5V power line up when unit is switched
on and cuts off power from the battery. There is a capacitor that permits
changing the battery without losing what is in memory. Also there are the
memory chips, the battery sensing chip, and the battery pack of three AA
1.5V batteries. Oh yes, there is the cable that attaches the battery pack
to the board.

I removed the battery pack container and measured the voltage across the
external terminals with NEW batteries installed. Even though each battery
measured 1.5V separately, I measured 3.7V across the terminals with the
three AA batteries inserted. This slowly dropped to 3.3V. Interesting.
Particularly when the battery pack is not connected to the board! I then
plug in the battery pack into the board and after the battery reading
stabilizes (the capacitor is charged), the voltage reads under 2V. I unplug
it, and the battery voltage jumps to 4V. I think there is a connection
problem here. Otherwise this is not making any sense to me.

Any ideas? I am teaching myself how to repair this problem. I appreciate any
help!

Thank you!

Bob Graham

Obviously, something is drawing more current than the batteries can
deliver. I would be looking for a shorted or leaky cap somewhere.
Do you have a schematic? Your going to have to load shed to find out
where the high draw section is somehow.

Bob

 

[Robert Graham Jr.]

Hello!

I found out that the problem was a corroded terminal inside the battery
pack. Thanks for replying to my problem.

Bob Graham

Obviously, something is drawing more current than the batteries can
deliver. I would be looking for a shorted or leaky cap somewhere.
Do you have a schematic? Your going to have to load shed to find out
where the high draw section is somehow.

Bob

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