Automated Fixtures Fried control chip on a VL2500

[litemoves]

So... I just turned on a VL2500 Spot (2004-era). Just as it started to home, I heard the faint snap-crackle-pop of a failing circuit board, accompanied by the telltale smell of burnt plastic, and a decent amount of magic smoke wafting out the vents of one side of the yoke.

Sure enough, it appears that part of the pan driver IC (U31) on the Main Control Board has burnt up.

All heatsinks and screws were secure--in fact, I was checking the light for a lamp ballast problem, and had never touched the MCB, or even opened the yoke. I'm inclined to chalk this up as random chip failure from prolonged heat/age.

But here's my question: Assuming that all connections are intact and correct, is there any chance that, if I try another board, the same thing could happen?

 

[Wood4321]

More than 50/50 I would say.
If there is a problem in the wiring harness, such as an abraded wire that is shorting to ground, it will do the exact same thing as the first one.
I would do a thorough inspection of the wiring harness, especially where it travels through the yoke. I would also meter the motor and make sure none of the windings have shorted to ground inside the motor.

Usually driver chips don't smoke when they fail unless something caused them to fail..
Good luck.

 

[JD]

There is an old saying "If it doesn't pop in the first 72 hours, a chip will last forever." Now, needless to say, as with most of these types of sayings, real world proves them wrong. Still, there is some truth in that if a chip has a defect in it, it will go quite early in life. This is why many companies do a "burn in" on new equipment.

The older a unit gets, the less likely a chip failure was due to chip design or flaw. It is far more likely that something popped it. An over voltage, shorted harness, flaky motor. Look for something that tends to be more age related. For example, a harness moves and may have abraded. A motor moves, and may have worn out. Power supply may have bad caps and poor regulation.

Could the chip have just up and failed at that moment? yes. Is it likely? No.

 

[church]

There is an old saying "If it doesn't pop in the first 72 hours, a chip will last forever."

Every electronic component has a failure rate (the number of units failing per unit time) this is a function of the chip design and the process technology used to manufacture the device. In practice once you get beyond the "infant mortality" phase or the first 72 hours the Mean Time Before Failure (MTBF) of any circuit is a function of the circuit design, the operating temperature and the part stress (this is how close to the spec limit the part is operating). The infant mortality is often a function of the assembly activities: how hot did the device get during solder, any ESD etc. The MTBF can be calculated and the analytical models, techniques and databases for doing this are well understood - it is not cheap to do but it can be very beneficial. You can improve the reliability by of a circuit by reducing the "part stress" and/or temperature. For example we double the failure rate for power transistors for every 10 degree centigrade increase in junction temperature beyond 110C when performing a reliability analysis.

you can learn more about this at the link below.

http://www.epsma.org/pdf/MTBF Report_24 June 2005.pdf

 

[porkchop]

Meter out every connection you can that goes to that driver chip to ground. In my experience catastrophic chip failure like that usually is because something is shorting out.

 

[Wood4321]

Meter out every connection you can that goes to that driver chip to ground. In my experience catastrophic chip failure like that usually is because something is shorting out.

Good Call Brett,
But keep in mind that shorts in the harness are almost always intermittent. They often don't show themselves until the fixture moves. This makes it difficult to find a short on the workbench without removing the entire harness and doing a physical inspection.

 

[JD]

Normally, there is enough slack in the harness to pull it back and forth enough to inspect the usual suspect areas, such as the center shaft or pivot points. Bright light is also important as the clue will be a small metallic reflection often right as it enters a shaft.

 

[litemoves]

This is all great advice, thanks.

It looks like my first step will be checking the wiring for shorts.

Once that's done, does anyone know which pins I should be checking on the pan motor?

 

[JD]

This is all great advice, thanks.

It looks like my first step will be checking the wiring for shorts.

Once that's done, does anyone know which pins I should be checking on the pan motor?

Most motors in movers are stepper motors which have 4 wires going to them. Two feed coil "A" and two feed coil "B." When the motor is disconnected from the harness, you should not see any leakage to the case from any of the four pins. You should see a low resistance between two of the wires and low resistance between the remaining two, but again, there should be no leakage between the two sets. The readings you get should be pretty close resistance wise when comparing coil A and coil B. Beware if either coil reads as a short or is radically different then the other coil.

 

[litemoves]

Most motors in movers are stepper motors which have 4 wires going to them. Two feed coil "A" and two feed coil "B." When the motor is disconnected from the harness, you should not see any leakage to the case from any of the four pins. You should see a low resistance between two of the wires and low resistance between the remaining two, but again, there should be no leakage between the two sets. The readings you get should be pretty close resistance wise when comparing coil A and coil B. Beware if either coil reads as a short or is radically different then the other coil.

The pan and tilt motors have 4 pins but only use 3 wires (all others in the VL2500 use 4). My limited stepper-motor research tells me that it probably has three windings with a common return, rather than two separate windings? In any case, I have a brand-new motor to compare it to, so I'll just meter across the pins and see if they match the good one.