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Author Topic: Xetrol Dimmer Delayed "UP" Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-07-2017 08:16 AM                    I have a couple of venerable Xetron Xetrol dimmers. They are in the adjacent electric closet and remoted to the booth. The remote buttons are similar to those on the units with indicator lamps. One of them takes its own sweet time responding to the UP button. Wait a while and then it comes up. I'm trying to find the cause. The issue is variable. Sometimes the ramp up begins right away; sometimes the long delay. Pressing the dim button and back to bright, more than once, while this is going on doesn't seem to do much. It's not a button issue nor, I think, a relay issue as the indicator lamps respond immediately. Just in case I replaced the UP relay on that unit. I have also swapped control circuit boards. That doesn't leave too much: Principally the triac "Power Cube," the power supply, and the big inductor. The dimming ramp down works normally. This unit has the external "Emergency Full Up" apparatus attached, if that makes any difference. That works normally. (Who'da thunk external gear was needed for that rather basic feature?) Thinking maybe it's a dirty contact on the ramping speed pot I worked that back and forth a bunch of times but so far as I can tell that control is working normally: After the delay the dimmer ramps up in accordance with that pot's setting, faster or slower. There are a few little odds and ends on the motherboard: A couple of resistors and a couple of small caps. I wonder if this might be where the issue is. Years ago I had to replace a Power Cube but I was totally dumbfounded when, on a different occasion, the unit failed and no amount of swapping of parts would get it going until I investigated those mother board resistors and found one open. Maybe someone has been down this road before as these were once common.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-07-2017 10:25 AM                     Have you tried spraying contact cleaner on the circuit board contacts  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-11-2017 06:35 PM                    I have now tried lightly sandpapering the contacts on the socket (as well as the board though that was already absolved by swapping boards). No effect. What I have noticed is that it is definitely related to ramping speed. If cranked up to very fast where it is nearly straight on, the response is swift. If set to a more modest speed, where the ramp-up is over just a few seconds, which is still pretty fast, the response is so slow you think it was never going to come up at all. In testing today it took maybe two minutes before it started the several second ramp-up. I suppose I should check the values of the motherboard resistors. I may try swapping the triac "Power Cubes" in case there is something funky going on there.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 03-12-2017 02:22 PM                        Remember that control runs from instant to 30+ minutes; very sensitive.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-12-2017 02:56 PM                    Yes, but the ramp-up I am seeing is what I am expecting it to be...once it starts. If it was ramping up over several minutes that would be one thing. But zero (apparent) output for two minutes and then a 15 second ramp-up isn't right. Guess I need to get out the thermal paste and try swapping Power Cubes. Maybe one of the triacs is funky. I'm sure I am getting both sides of the waveform. My "up" is a little less than full waveform but if I turn it up to full on (or use the emergency full up feature---which still flows through the Power Cube) the lights are certainly full so it's not like one triac in the cube has expired. And for the record these are ordinary incandescents; 12 100W bulbs on this unit.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-12-2017 09:25 PM                     Just recap the bastard and then reset the controls. The caps in those dry out and they behave strangely. Also, there is a unijunction transistor on the control board that is NLA, at least not easily available. If that is failing they will operate very inconsistently. Several months I recapped three of them and they all worked fine afterwards. Mark  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-13-2017 02:49 PM                    What caps, Mark? As you know I tried swapping boards and nothing changed. That's where the only electrolytic is.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-13-2017 03:33 PM                     If that substitute board works in another dimmer ok, then the issue is elsewhere. Next thing to do is to swap the Triac. Those can also become flaky, and also check your neutrals. They should not be shared with the feed. Beyond that stuff there is nothing to try. It's such a simple dimmer that the next step is known as a Kelmar House Light Dimmer swap out. And you;re using incandescent lamps I assume... Not all LED bulbs work with dimmers correctly. Cree lamps do work ok. Kelmar has an approved list and a special accessory load that will cause some others to function ok. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-14-2017 09:57 AM                     The triac probably is not the fault if they get flacky it is usually flickery If the lamps you are dimming they will have a different fade curve on the up cycle nothing will happen until the threshold for the ballast is reached and it kicks in also the load may be to small for the triac or SSR block to fire  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-16-2017 06:46 PM                    Same old every day 100W medium base light bulbs as I've been using for years. I'm leaving the ramp setting for fairly fast which eliminates most of the delay for now but it's rather inelegant. I agree the triac pair is unlikely to be the culprit as they ramp down just fine not to mention also are fine with the full-up emergency mode. I am somewhat suspicious of the two resistors on the motherboard, R7 & R8 or even the caps in parallel. Thought they were 220 Ω but a quick check showed a lot less but that's in-circuit and might be meaningless. I will take another reading with the control card pulled which should be sufficient for a valid measurement. And also compare with good dimmer. I can always just swap entire dimmers. The other one just does screen wash and it's not critical how long that would take to come up.  |  IP: Logged Bob Ezra Film Handler Posts: 75 From: Carbondale, CO, USA Registered: Apr 2001 posted 03-20-2017 11:33 PM                     I have replaced the innards from one xetrol to another and it was working fine. Now they occaisionally (twice during one recent show) surge up and down slighty. Is this the " The triac probably is not the fault if they get flacky it is usually flickery" that Gordon refers to. If the lights do this, is it the Triac and if it is where can I get a new one and what's involved in replacing it? Thanks  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 03-23-2017 07:52 AM                    I'm no expert but if you have a known good control board I would try that first. As for the power cube, some advice I got online years ago... Steve, I think the Silicon Power Cube brand has become absorbed through a series of acquisitions and mergers into the Crydom brand. Your pictures show what looks like a dual SCR module. From your description of the application, I'll bet that the Crydom B551SE-2T or B561SE-2T (or equivalents) will work for you. The datasheet is at The posted link is obsolete but you can see one here. http://www.mouser.com/ds/2/657/B_2T-1063166.pdf (if this link eventually fails just Google the part number). I believe the originals were rated 35A. If you need the capacity get the B561 (42.5A) otherwise the 551 (25A) would suffice. It's been years but I think I have the latter in one of mine. (My two circuits are pulling 600W and 1200W.)  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-23-2017 01:06 PM                     quote: Steve Kraus (My two circuits are pulling 600W and 1200W.) Ha? How did you measure that? I have 400 seat locations that don't even pull a quarter that much...  |  IP: Logged Buck Wilson Jedi Master Film Handler Posts: 894 From: St. Joseph MO, USA Registered: Sep 2010 posted 03-23-2017 03:32 PM                     4 wall sconces on 2 walls with 2 75watt bulbs each equals 1200w, seems pretty reasonable to me  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-23-2017 05:52 PM                     No one I know uses 75 watt lamps turned all the way up. Mostly 40 & 60 watters probably at about 30% and lower. Unless your room is all black inside. Most of my customers have since gone to Cree LED Lamps, so the wattage used now is really insignificant on their power bill. Steves room is perhaps 30 seats. Mark  |  IP: Logged

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