Need Help!- Brushed VF-2 Servo Distribution Board Regen??

[DaOne]

Can someone tell me what the purpose of this resistor is? I fully understand what its for on the spindle (brake) but why is there one on this board? It appears as if its controlled via clamping the 160 volt buss through the resistor via an IGBT. Anyways I think the IGBT is bad because the resistor is always applying power to the resistor no matter what the condition even when the power is turned off. It also blew the 2 white wire wound resistors that are 300 ohm. Haas wants $500 for another board with exchange. There isn't $100 worth of components on this board so I think I am gonna fix it myself. Just trying to understand why there is this circuit there to begin with.

[DaOne]

Nobody knows anything about this board? I have ordered all the parts for it. I will post the results. After reading though the forums I see that quite a few others have experienced the same problem I have now. If this fixes the issue it will hopefully save others a chunk of $. I am almost sure that I know what caused the failure. I just wish I knew why this circuit is in place to begin with.

[DaOne]

Parts came today. Soldered in place and all is great. Good as new! If anyone runs into this issue the fix was replacing...

(2) 300 Ohm 5 watt resistor
(1) IXGH24N60AU1
(1) LM339N

[Donkey Hotey]

Thanks for posting up the details. I don't know if anybody has tried to repair one of those boards but, I'm sure the regen resistor does the same thing that it does for the spindle: provide electric braking for the axis it's attached to. As you figured out, if that IGBT shorts, it will overheat the resistor.

[DaOne]

Originally Posted by Donkey Hotey Thanks for posting up the details. I don't know if anybody has tried to repair one of those boards but, I'm sure the regen resistor does the same thing that it does for the spindle: provide electric braking for the axis it's attached to. As you figured out, if that IGBT shorts, it will overheat the resistor.

Well the way the circuit is configured there is no way it can provide a brake. Basically when the IGBT is switched on it applies the direct 160 buss voltage directly the the regen resistor. Basically it becomes a parallel circuit. Like I say I have no idea what this would accomplish other than a small space heater? The IGBT wasn't fully shorted but did have a big leak. It also leaked out the gate and fried the LM driver chip. Since the relays were not switched on due to the low voltage on the buss the buffer resistor on the board became the only path of current. Since they are only rates for 5 watts they cant handle powering the regen resistor for very long before they fail as well. Now i am on to fix the A axis board. its drawing quite a bit of current while idle. (More that all three other axises even when my 4th axis is disconnected) The board appears as a fancy H bridge DC motor controller so I should be able to track it down with a scope. I really wish replacement parts for such an old machine didn't cost so much. I don't think the price has changed any from when they were the latest and greatest.

[Donkey Hotey]

I'm no electronics expert but, I think that's exactly what the IGBT is there for. My guess is that the IGBT switches the motor from the DC buss coming in, over to the regen resistor during slow down (the DC motor is back-driven by the moving mass, becoming a generator). I haven't actually worked on one of these but, that would be my guess.

The connection and symptoms you're describing sound similar to an IGBT failure in a vector drive; the regen resistor gets to glowing on top of the cabinet whenever the servos are engaged and the vector drive throws an error. That sounds like the same symptoms you're describing but, with an axis amplifier.

[DaOne]

Originally Posted by Donkey Hotey I'm no electronics expert but, I think that's exactly what the IGBT is there for. My guess is that the IGBT switches the motor from the DC buss coming in, over to the regen resistor during slow down (the DC motor is back-driven by the moving mass, becoming a generator). I haven't actually worked on one of these but, that would be my guess. The connection and symptoms you're describing sound similar to an IGBT failure in a vector drive; the regen resistor gets to glowing on top of the cabinet whenever the servos are engaged and the vector drive throws an error. That sounds like the same symptoms you're describing but, with an axis amplifier.

Well the board I am talking about is a power supply for all the axis boards. They all share the same power source. Its purpose is to output approximately 160 volts to all the axes boards (Servo motors), Provide 16 and 4 volts for the logic on the axis boards, send a monitor reading for buss voltage (servo motors) to the panel, send over voltage alarm signal to the console, chop power to the axis boards when in an alarm condition and (shunt excess power to a resistor???). If it was going to be used as a brake it would be a separate output from the axis boards so it doesn't interfere with the other axises it shares power with. I feel this one is in place as some sort of over voltage protection.