Film-Tech Forum ARCHIVE: LEPCO Dimmer fried, any ideas?

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Posted by Aaron Sisemore (Member # 145) on 02-01-2002, 12:13 AM:

About a week ago, the electrician was changing out damaged overhead light fixtures in one of the auditoria, and in the process accidentally drove a screw thru one of the hot wires. After clearing the obvious short, the power was reapplied to the lighting circuit, but the dimmer would not operate (lights stay on full and will not dim). The side lights are on another module in the dimmer and still worked.

Assuming it was a blown triac, I first tried swapping the triacs between the always-on side and the still functioning side light module, and nothing happened-pitch dark. Figuring that for some morbidly stupid reason both triacs had to be in-circuit to make things work at all, I hit the road and went around looking for another triac to replace it with, and was unable to obtain an exact unit, but got a crossreference to another type.

Installed the new triac to the once-working side light module and replacing a wire I had unintentionally disconnected from the overhead light module (why there was darkness after swapping triacs) I hit the power, and all the lights came up full... but would not dim!

The dimmer is a LEPCO (Lehigh Electric Products) dual module unit (large blue box with slide pots to control brightness and dim rate). Any ideas to get this thing working again after dropping $78 for three triacs (we have two more of these dimmers in other auditoria so I figured the spares were worth getting, just in case) before I get really upset and rip it out of the wall and replace it with a pair of Xetrol IVs??

-Aaron

Posted by Ken Layton (Member # 133) on 02-01-2002, 12:41 AM:

Not being familiar with your particular brand of dimmer, I can give generic troubleshooting tips.

It's possible that another component was damaged on the control board that operates the affected triac such as a driver transistor/ic, diac, or a burnt resistor. It's possible that a foil trace could have been burnt/blown off the pc board. Check for burnt/damaged connectors.

If I had a schematic of your dimmer I may be able to assist further.

Posted by Paul G. Thompson (Member # 655) on 02-01-2002, 12:42 AM:

Xetrol IV's? Nah. They are obsolete. But they were a very good dimmer in their day. Biggest thing with them now is they don't have half-light provisions. If you don't need that provision and you have some Xetrol IV's laying around, then go for it.

Posted by Steven Gorsky (Member # 603) on 02-01-2002, 01:40 AM:

I actually happen to have a copy of the "Installation, Operation, and Maintenance Manual for the Movie-Pak Dimming Systems Series C" which should be for that dimmer (if it is from the mid-80s), which I've been meaning to scan and send in, but it does not contain any schematics

It does however list the following as troubleshooting tips for when the lights will not go out:

1. If the system has the Panic function, check that the relay is not in the panic mode. Go to a remote station and pulse the Panic switch to the Normal position to release the panic relay. The panic relay can also be operated at the dimmerboard by pulsing between the 35+ terminal and the P and N terminals. If the relay is operating properly, it makes an audible click when it is pulsed. If no noise is heard, the relay may be stuck in the panic mode due to crossed wires going to the remote station or malfunction of the relay. To check for crossed wires, remove the wires running to the remote statiob and operate the relay manually as described above. If the relay now works, check the wiring to the remote stations.

2. Check the output on the fader control module card. When the Lower signal is pulsed, the output voltage between SIG and C on the control card should drop from 24V DC to 0V. If the output voltage does not drop, the control module is defective and should be returned for repair.

3. If the fader control card module is working, the dimmer is probably defective. Interchange the bad dimmer with one that is working. If the problem follows the bad dimmer, it should be returned to the factory for repair. To test a dimmer when a spare dimmer is not available, remove the plug from the control card module and if the lights do not go out the dimmer is bad.

Lehigh is still around, their website however doesn't have anything on this dimmer. However they can be reached at (610)395-3386, Monday through Friday 8am until 5pm, or by e-mail at service@lehighdim.com

Steven Gorsky

Posted by Steve Guttag (Member # 268) on 02-01-2002, 06:38 AM:

Excellent post Steve!

------------------
"Old projectionists never die, they just changeover!"

Posted by John Walsh (Member # 168) on 02-01-2002, 10:08 AM:

Not directly related; but I occasionally work at a theater with dimmers made by Panja Lighting. The theaters are small, with simple lighting needs. Well, to change the settings, you must use a laptop and plug into the serial port on the dimmer.

It is pretty cool, but this stuff is sure getting complicated.

Posted by Steven Gorsky (Member # 603) on 02-03-2002, 06:11 PM:

Thanks, Steve!

BTW, Aaron let us know if you find the problem.

Steven Gorsky