Film-Tech Forum ARCHIVE: Xetrol Dimmer Delayed "UP"

This is topic Xetrol Dimmer Delayed "UP" in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=012119

Posted by Steve Kraus (Member # 476) on 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.

Posted by Gordon McLeod (Member # 33) on 03-07-2017, 10:25 AM:

Have you tried spraying contact cleaner on the circuit board contacts

Posted by Steve Kraus (Member # 476) on 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.

Posted by Louis Bornwasser (Member # 3063) on 03-12-2017, 02:22 PM:

Remember that control runs from instant to 30+ minutes; very sensitive.

Posted by Steve Kraus (Member # 476) on 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.

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Steve Kraus (Member # 476) on 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.

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Gordon McLeod (Member # 33) on 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

Posted by Steve Kraus (Member # 476) on 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.

Posted by Bob Ezra (Member # 841) on 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

Posted by Steve Kraus (Member # 476) on 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.)

Posted by Mark Gulbrandsen (Member # 72) on 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...

Posted by Buck Wilson (Member # 5885) on 03-23-2017, 03:32 PM:

4 wall sconces on 2 walls with 2 75watt bulbs each equals 1200w, seems pretty reasonable to me

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Steve Kraus (Member # 476) on 03-24-2017, 10:43 AM:

Mark, that would be at full tilt: 6 and 12 lamps, each with 100W bulbs. The main dimmer (the problematic one right now) has the panic button feature that brings them instantly up full. There are no work lights so smaller bulbs would not be effective. Our normal "UP" is a little below max. I have one critic who routinely hits the panic button when entering the room just for those few added lumens. When I see this I always take it back to normal. It's a little game.

Anyway....

And the winner is...

(If you're dying to know skip to the last graph.)

I pulled the control card to get proper readings of the two motherboard resistors. They checked out though the bottom one seemed like it might be open but I put that off to poor contact of the meter probes.

So I opened the good dimmer and proceeded to swap the triac power cubes. As expected, no change. But curiously, the lower resistor on that one looked discolored. I wonder if the unit overloads it or maybe aging control card characteristics (both of them) was responsible.

So the next step was to replace that resistor. A big job since these dimmers are 7' up on the wall of the electric closet so it takes at least 20 minutes to disconnect all wires and pull out the chassis.

So got it in the booth, hooked up a power cord and a 100W bulb. As I did not have a higher rated 220 ohm resistor I decided to spread the load over 3 in series adding up to the same amount.

Along the way I noted that no resistor in that spot produced the same result: Minutes would go by but eventually the lights would rise. Odd because I thought that resistor provided the gate power to one of the triacs. Any, replacement with the correct value did not solve the delay issue. Nor did experiments with higher or lower values. I left it with a single resistor as built.

Hmmm....running out of potential faults.

At this time I noted a curious thing. If you are in bright mode and hit the dim button, the dim relay clicks and electrically latches in. But if dim and you it the bright button the bright relay (which I had replaced) continues to respond momentarily. It clicks in with subsequent button pushes. (I checked if holding the button brings the lights up faster but it does not.) Something seemed wrong about that.

However this proved to be a red herring. I checked the good dimmer and it works the same way. Oh well.

But thinking about the relays drew my attention to the DIM relay which was still original. I replaced it. Problem solved. So, the delay on bright was caused by a faulty DIM relay. With a good relay in there and controls back to how they were there is still an 8-9 second delay before the ramp up starts but I think that's how it always was. Before posting I felt compelled to go back and recheck that I had not been spacing about which relay is which but, yeah, the dim relay caused the problem.

Posted by Mark Gulbrandsen (Member # 72) on 03-24-2017, 02:03 PM:

Not too surprising as there is a path through the dim relay for the up relay, and that set of contacts were obviously bad. While I have never seen that happen in a Xetrol dimmer before, I have seen it happen in Kelmar automations. Dimmers made in the last 25 or so years don't typically have relays....

Mark