MT1000 Charger(NTN4633C) Completely Dead
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MT1000 Charger(NTN4633C) Completely Dead
MT1000 Charger(NTN4633C) failed completely. Fuse from bottom holder checks OK. Are ther any common internal compenent failures to check? Thank you
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Tom in D.C.
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Re: MT1000 Charger(NTN4633C) Completely Dead
1. The AC output from the transformer. Is it there?
2. The condition of the diodes in the rectifier string, whatever type it may be. Bad diodes will
read zero ohms both ways with the test prods. Good diodes will read a short in one direction and resistance in the other.
3. The condition of the three-terminal voltage regulator. It should have a high input voltage
and a regulated output voltage among the three pins.
4. Cold solder joint(s) on the circuit board.
Do the resistance checks with the POWER OFF. The voltage checks are done, carefully,
with the POWER ON.
At some point under 1, 2, or 3 you should have no voltage. Use a digital volt/ohmmeter;
that's the only reliable way to check voltage, current, and resistance these days.
2. The condition of the diodes in the rectifier string, whatever type it may be. Bad diodes will
read zero ohms both ways with the test prods. Good diodes will read a short in one direction and resistance in the other.
3. The condition of the three-terminal voltage regulator. It should have a high input voltage
and a regulated output voltage among the three pins.
4. Cold solder joint(s) on the circuit board.
Do the resistance checks with the POWER OFF. The voltage checks are done, carefully,
with the POWER ON.
At some point under 1, 2, or 3 you should have no voltage. Use a digital volt/ohmmeter;
that's the only reliable way to check voltage, current, and resistance these days.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
Re: MT1000 Charger(NTN4633C) Completely Dead
The MT1000 charger doesn't have a 3 terminal regulator, it uses a TIP-32A pass transistor mounted on the metal chassis.
There are 5 large screws on the bottom and on small one, remove the 5 larger phillips screws and leave the smaller one alone to gain access to the insides.
You'll see the pass transistor between the main circuit board and the power transformer it is a TO-220 device with an insulated tab to the heatsink.
The pass transistor requires a mica thermal pad between its tab and the metal heatsink, I'd check this first to see if the pad wore out and shorted the transistor tab to the heatsink.
Remove the tab mounting screw and pull the screw out and gently lift the tab away from the heatsink and inspect the mica thermal gasket.
Measure the resistance from the transistor tab to the heatsink, it sould be high or measure as an open.
Next measure between the 2 outer pins of this transistor and it should be 68 ohms, if lower than this then the transistor is damaged.
Other things to check:
Like Tom says check the power transformer first at points A and B on the circuit board, this should measure 20 volts AC on points A to B.
Next look for the large electrolytic cap in the lower right of the PWB measure the plus terminal to a ground area on the circuit board and it should be 27 volts DC.
Other things to check unpowered are the large resistor on the back side of the circuit board rear, this is a 2 ohm 7 watt resistor (R14).
Next look for the next largest resistor which is a BLUE leaded one near the PWB top just to the right of center and it should be marked 430 ohms, now look for the resistor that is directly below this one.
Measure this resistor to make sure it hasn't changed, depending on what mods were made to your charger this resistor could be either 22 ohms or 68 ohms.
Next look for a BLUE thermal protector, RV-1, near the bottom of the circuit board to the left of the large electrolytic cap and measure this from the circuit board backside, this is around 330 ohms. This looks like a large disk capacitor.
If all checks fine then like Tom says, look for cold solder joints.
Your charger could have had a some after market mods to it to lower the trickle current and to change the turn on state so that the charger doesn't come up in fast charge mode until a battery is inserted and the modifier could have made some poor solder joints.
Mike
There are 5 large screws on the bottom and on small one, remove the 5 larger phillips screws and leave the smaller one alone to gain access to the insides.
You'll see the pass transistor between the main circuit board and the power transformer it is a TO-220 device with an insulated tab to the heatsink.
The pass transistor requires a mica thermal pad between its tab and the metal heatsink, I'd check this first to see if the pad wore out and shorted the transistor tab to the heatsink.
Remove the tab mounting screw and pull the screw out and gently lift the tab away from the heatsink and inspect the mica thermal gasket.
Measure the resistance from the transistor tab to the heatsink, it sould be high or measure as an open.
Next measure between the 2 outer pins of this transistor and it should be 68 ohms, if lower than this then the transistor is damaged.
Other things to check:
Like Tom says check the power transformer first at points A and B on the circuit board, this should measure 20 volts AC on points A to B.
Next look for the large electrolytic cap in the lower right of the PWB measure the plus terminal to a ground area on the circuit board and it should be 27 volts DC.
Other things to check unpowered are the large resistor on the back side of the circuit board rear, this is a 2 ohm 7 watt resistor (R14).
Next look for the next largest resistor which is a BLUE leaded one near the PWB top just to the right of center and it should be marked 430 ohms, now look for the resistor that is directly below this one.
Measure this resistor to make sure it hasn't changed, depending on what mods were made to your charger this resistor could be either 22 ohms or 68 ohms.
Next look for a BLUE thermal protector, RV-1, near the bottom of the circuit board to the left of the large electrolytic cap and measure this from the circuit board backside, this is around 330 ohms. This looks like a large disk capacitor.
If all checks fine then like Tom says, look for cold solder joints.
Your charger could have had a some after market mods to it to lower the trickle current and to change the turn on state so that the charger doesn't come up in fast charge mode until a battery is inserted and the modifier could have made some poor solder joints.
Mike
Re: MT1000 Charger(NTN4633C) Completely Dead
Thanks for the replies guys - will try the above when schedule allows ASAP