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2020 ST20Y - Power outage = Alarm 648: DC BUS SHORTED


Jan 10, 2019
State College
  • 2020 ST20Y
  • ~250 cut hours (yes, very low - arguably a bad purchase, but it is nearly paid off)
  • Power supplied by Phase Technologies PT030 w/ their surge protection kit (it is my limited understanding that the digital converters are helpful in isolating potential power problems downstream. Spikes, dips, irregularities, etc.)

    On Monday the power dipped enough at the beginning of a storm to shut the machine down. The phase converter fired back up effortlessly and has no signs of any problems. It is supplying the same steady voltage across all 3 legs as it always has.
    I was just finishing running a few extra parts for the run I was doing and decided to just leave the machine off for the day, knowing I could run a few more the next day or two when I fired it backup for a new setup.
    Yesterday I booted up the machine and as soon as I power up/restarted the machine is alarmed out. Alarm 648: DC BUS SHORTAGE
I pulled up the above guide and proceeded to check the regen resistance under "Regen Load"
I assume 4 coils = 4 resistor box.
I measured 5.7-5.8 ohms indicating the regen is not the problem.
I proceeded to check the resistance at the vector drive across t1 and t3 and am seeing .1-.3ohm (short).

Without doing any other testing, HFO is telling me that my drive is faulty/dead. I accept that life sucks sometimes and ask for quote while doing some research on repairs, etc.

HFO will not answer me as to if power outages can/do have the potential to cause this (I understand this may be a hard question to answer black and white, but they ought to know if sudden drops in power can take out a 6k component)
HFO also has not answered if this can be replaced by non-hfo tech and if a usb key is needed to do so. They list the part as needing to be installed by HFO tech on the parts website and cannot be purchased online, must go through HFO. Anyone know?

  • Does anyone have the unfortunate experience of having incoming power hiccups take out their vector drives?
  • Is it more likely that this drive had an issues and the stars aligned?
  • If incoming power problems can have a chance at taking out components, is there anything that can be done, purchased, devised to try to mitigate or eliminate this from happening in the future?
You seem to know something about multimeters so lets do this. If you haven't bought a vector drive yet, hang on.

First to get you amply familiar with how to not kill yourself. The 320V DC bus runs all the servo amps in these machines. It's deadly, blah, blah. After you shut off the power, there is a red indicator light that glows as long as the capacitors have a charge. It slowly fades out. Some people wire up a couple of old incandescent bulbs in series and use them with a jumper wire to discharge the capacitors after shutting down the power. I've done it. I don't recommend you do it. You're on your own.:D

The way 320V power works in Haas Vector Drive machines:
  1. AC power comes in from the source at the top of the cabinet.
  2. Goes through the circuit breaker.
  3. Goes through a big main contactor (relay)
  4. Goes to the transformer.
  5. AC comes out of the transformer outputs to the Vector Drive at terminals 4, 5 & 6.
  6. The vector drive has a full six-way bridge rectifier that turns the AC into DC (commercial part)
  7. The newly rectified DC connects to a bank of big capacitors (commercial parts)
That's all there is to making the 320V DC. It's all stone-axe simple. On the older models and probably the new ones, it's a commercial rectifier. It'll have a part number and can be bought if it's the problem. I'm not positive that this can be exclude this as a problem because the error might be reporting a few different types of failures. The rectifier is not my first suspect though. My guess is a shorted rectifier would pop the incoming circuit breaker, not throw an error.

From the rectifier in the Vector Drive, 320V DC is supplied to terminals 2 and 3. If you trace those wires you'll discover they go to each of your axis servo drive amps. The reason I drag you through this is that entire run of wire is the "DC bus." A short could be anywhere along that run. I would start by disconnecting the black and white wires labeled 325VDC to Servos from the Vector Drive. Restart the machine and see if the error is still there. If you still have an error, it's inside the vector drive. If you don't, one of your servos has the short.

The "Vector Drive" is nothing but a big version of the servo amps running the other axes except that it includes the DC power supply section. So the Vector Drive has a 320V DC bus. How does it run the power out to the spindle motor (terminals 9, 10, 11)?

There are three large IGBTs (Integrated Gate Bipolar Transistors) inside the Vector Drive case. These are also commercial parts. My money is on one of the three transistors having died. I don't know if you have the 20 or 40 HP vector drive so be aware these kits may be different:

This is a complete "repair kit" for the 20 HP drive. He also has a 40 HP model. You probably don't need all these parts. Each of these can also be individually tested if you open up the case and remove some screws. Take pictures with your phone (preferably of the inside of the vector drive and not yourself) as you go and it should be fine.

The white things in the third picture are the IGBTs. The big black thing with 5 terminals is the rectifier.

My guess is that if the bus has a short inside the Vector Drive, it's one of those IGBTs to blame. The Servo Amps behave much the same way, except the transistors are smaller and all soldered to the boards. If it's a servo amp causing the issue, it's a replacement item unfortunately.

In the case of servo amps or the vector drive, you can usually do the replacement but, there is no warranty and no return for self-repair. They don't want people misdiagnosing wiring and motor problems and blowing up good components. I kind of see their point but, it would suck to drop $6K on a vector drive and blow it up because a servo amp had a dead short and was the actual cause.

To put your mind at ease: my 2004 VF-2 crapped the vector drive about two months out of warranty, with lower hours than your machine. That's why I know so much about the innards. I wasn't giving up that money without a fight. My failure was a 123 error which was related to the electronics drive side of the unit and not the bus like yours.

Oh, also: I had the pleasure of working on a VF-5 when we had regular, summer brown-outs. Lonnnnggg power dips and the occasional outage. It never took out a vector drive. I think you just had bad luck.
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I am having a similar issue , error 468 dc bus short.
On removing the regen wires from the vector drive the error goes away and machine will power up as per normal but no regen .
I removed regen and checked for resistance - 7ohm which is within spec for the 3 coils , tested each coil and all wiring for any shorts to earth - nothing.

Issue has to be inside the vector drive regen circuit - what to check next ? internally in the vector drive. - does anyone have a wiring diagram for a 20hp vector drive ?