Vintage Lighting Scrimmer Troubleshooting and Repair

[JD]

No problem. I'm going to dig out a hand written copy of the ramp generator circuit and scan it. As long as you can get the test light to light by pushing the button while the module is in failure mode, the the problem is in the ramp generator part of the circuit as that is the only circuit both channels share.

 

[WestportLights]

While both channels do go out, it is not at the same time. One channel always drops before the other, the amount of time between the two drops is seemingly a ratio of how long they stayed on. They stay on longer if you let the module's breakers stay off for a while (cooldown or capacitor discharge perhaps?). If you reset the failed module's breakers right after they drop out, the channels do not stay on for very long.

I'm talking a difference of 3 seconds to 3 minutes in the first channel going out after reset. and ~.25 seconds to 15 seconds for the second channel to go out after the first.

 

[JD]

Ok, below is a generic layout for the EDI ramp generator. You can see the 12 volt winding in the upper left hand corner. It feeds into the bridge rectifier and then goes through a diode before hitting the main filter cap, which supplies power to the rest of the circuit. Note how unfiltered power feeds down to 1/4 of the quad op amp. This part of the circuit is the "zero voltage cross detector" and produces a pulse whenever the AC waveform starts. The output waveform is a square wave with a 1% / 99% duration and a frequency of 120 cps. It goes through a 1k resistor, then a diode, and then into the 2nd 1/4 of the quad op amp. This part of the circuit produces the ramp and is the heart of the dimmer. There is a little notation that the thermal shut-down shorts the output when it kicks in (right after the resistor) which turns the dimmer off when overheated.

The upper right shows the four stages of ramp generation. Steps 1 and two happen real fast!
1) The ZVCT goes high, using the 2N4401 to discharge the ramp capacitor. (.1 mfd)
2) When the cap is discharged the ramp output goes way high. (about +14 volts)
3) The ZVCT goes low and the output of the generator drops to the high-end set point, 7.6 volts.
4) As the cap charges, the output curves down to the low end set point of 2.6 volts. Then the whole thing starts over!

So, what is not shown is that the ramp output feeds the other two sections of the quad op. These also get the control board output. When the two voltages cross, those sections produce a pulse which is buffered and drives the opto-isolators. Failures in either of those two circuits would only take out one dimmer channel.
If the .1 mfd ramp capacitor had any leakage or was open, you would not get any ramp. Caps can get flaky and noisy, so short of setting up a bench jig, that would be a cheep try. Next in line would be the quad op-amp. It may fail shortly after power is applied due to a substract crack in the circuit, which would explain why it works after power is removed. It's a cute little circuit to watch working on a scope!

EDIT: Just saw your post. If the duration can be that long before the second channel goes out, then it sounds more like a thermal problem with the quad op-amp.

 

[WestportLights]

Does the quad op amp have a different modern number? The one on it has:

UA3403PC
F7711

I can't seem to find it available anywhere.

 

[JD]

Does the quad op amp have a different modern number? The one on it has:

UA3403PC
F7711

I can't seem to find it available anywhere.

Here's one set of crosses:

Fairchild UA3403PC Replacement Parts & Analogues | All Cross Reference Guides

I suspect there are many more! You used to be able to get a replacement right off the rack in Radio Shack!

It also crosses to the generic NTE line, NTE987

http://www.nteinc.com/specs/900to999/pdf/nte987.pdf

Looks like they are about $2.50 at mouser, who lists them in stock-
http://www.mouser.com/Search/Refine.aspx?Keyword=NTE987

If you are ordering from mouser, you may want to browse for a few of the other parts as it's no use paying all the shipping for one IC. The carry almost every part on that board.

 

[WestportLights]

The only quad op amp that radio shack had was LM324

I have a ua3403 coming but it's gonna take me a few days to get one due to the weekend and shipping.

 

[JD]

Actually, the LM324 crosses to a NTE987 as well. Not sure of the quality of the RS parts these days, but you could replace the current IC with a 14 pin DIP socket (which I think RS has) and just plug it in there.

 

[WestportLights]

JD, You're my HERO! It's up and running now all thanks to you!

I went to Radio Shack and bought the components that they had in stock, figuring I'd special order online what they didn't if their stocking items did not fix the problem. Well? It fixed it. Here's what I replaced.

Large Cap near transformer
Poly Caps
Transistor
Quad Op Amp



I also had to replace the fuse because the old one blew the second the unit got power, I assume it was on it's last leg but that sure threw me for a minute.

Yes, it was probably the quad Op Amp as you described. I likely could've done a cheaper repair by replacing one piece and testing, but warmup time on the soldering iron and removing the control board and replacing it several times was not worth reducing the $11.00 total cost spent at Radio Shack for the parts to 'shotgun' it.

I truly appreciate your time, knowledge, and expertise in this. I have learned so much by this problem that I'm almost glad it happened . . . well, maybe not. PM me your mailing address, I want to send you a token of appreciation

Also, I did contact several repair shops that were mentioned in an above post. Some no longer service this unit, one did not have the proper setup for bench testing, another said he could borrow a bench tester from another person, and one said they would attempt to fix on a 'best effort' basis. So, it's not like repair shops were jumping to help with this problem anyways.

 

[JD]

Glad I was able to help. Nice to put this antique knowledge to use sometimes.

 

[utilityman]

Glad I was able to help. Nice to put this antique knowledge to use sometimes.

Does anyone have a source or model cross-ref for the Heinemann Magnette 20Amp breakers in a 2.4kw scrimmer pack? My late-80s era Macro Electronics house lighting system uses the same part, but I've had little success finding modern equivalent. Going to try to call Eaton/Cutler Hammer, but not optimistic, since Macro doesn't have a part listed, although still talking with them.

or does anyone know the specs of the breaker? Heinemann PN is 0912 . 120/240v 20amp. Screw terminal in and out for wiring. I assume it is fully magnetic, based on reading more modern Eaton catalogs, so it can run continuously near full load without tripping and without need to cool down after a trip.

Any help greatly appreciated. I found a PLC site that listed one for about $70 that was probably used. I'd much prefer to have a modern reliable source.

-Brian

 

[STEVETERRY]

Does anyone have a source or model cross-ref for the Heinemann Magnette 20Amp breakers in a 2.4kw scrimmer pack? My late-80s era Macro Electronics house lighting system uses the same part, but I've had little success finding modern equivalent. Going to try to call Eaton/Cutler Hammer, but not optimistic, since Macro doesn't have a part listed, although still talking with them.

or does anyone know the specs of the breaker? Heinemann PN is 0912 . 120/240v 20amp. Screw terminal in and out for wiring. I assume it is fully magnetic, based on reading more modern Eaton catalogs, so it can run continuously near full load without tripping and without need to cool down after a trip.

Any help greatly appreciated. I found a PLC site that listed one for about $70 that was probably used. I'd much prefer to have a modern reliable source.

-Brian

Heinemann 0912 breakers were discontinued many years ago due to an excessive failure rate, and there is no compatible cross to another manufacturer that I know of. Some entertainment lighting manufacturers had to redesign their equipment to accommodate Heinemann or Airpax E-frame magnetic breakers when the 0912 was discontinued.

ST

 

[DavidNorth]

I would suggest contacting Steve Short at Lite-Trol. 516.681.5288

David

 

[FMEng]

Well? It fixed it. Here's what I replaced.

Large Cap near transformer
Poly Caps
Transistor
Quad Op Amp

From the described behavior, it was almost certainly the large capacitor. Electrolytic capacitors are prone to aging from heat. Those dimmers run warm. It would work for a bit until the leakage current increased too far, and a rest would allow it to work for a bit longer. Electrolytics are usually the first suspects when the equipment produces a lot of heat, or has big caps located close to a heatsink. Many times I have revived broken equipment by shot-gunning the electrolytics.

Right behind the electolytics, most failures are caused by mechanical failures such as oxide film on connectors, bad pots, and %$#@! muffin fans.

 

[mkurzunski]

Hi, I work in a theater that relies solely on one of these Scrimmers and it has been good to them for many many many years. I just found another one sitting under the stage of another theater I work at and I'm now trying to integrate it into the system. My big question regards data cable. There is an analog control in on the back as well as a "accessory" out. My understanding of analog was that you couldn't daisy chain, but then, what is the "accessory" out for?

I appreciate any help.

 

[JD]

Ahhh.. Data might be the wrong word as it is a wire per dimmer, 2 to 7.6 volts controlling. You can parallel dimmer channel control lines so that a given board channel controls many dimmer pack channels. In other words, if you made up a "Y" cable with a male Jones connector facing the board, and two female Jones connectors plugging in to the packs, Each channel would then control 2 dimmers, one on pack A and one on pack B. I remember the accessory jack on the Scrimmeretts, but not on the straight Scrimmers. On the 'etts it was to provide external mastering for the controls on the front of the pack. There were no local controls on the Scrimmers. (I might be forgetting something, I'll have to go to the shed and look at one.)

To my recall, the 12 channel Scrimmers had a 15 pin male Jones on them. If the "accessory jack" is a 15 pin female Jones, then chaining is exactly what it is used for.

 

[mstaylor]

Hi, I work in a theater that relies solely on one of these Scrimmers and it has been good to them for many many many years. I just found another one sitting under the stage of another theater I work at and I'm now trying to integrate it into the system. My big question regards data cable. There is an analog control in on the back as well as a "accessory" out. My understanding of analog was that you couldn't daisy chain, but then, what is the "accessory" out for?

I appreciate any help.

There is a manual listed in post 5, it says you can stack dimmers and either assign them the same number or use a unique number, depending on how you want to use it.

 

[JD]

There is a manual listed in post 5, it says you can stack dimmers and either assign them the same number or use a unique number, depending on how you want to use it.

The manual listed in Post #5 is for the SCRimmerette II. These do have a digital option. If your pack looks like the one in Post #1, then that is a good old fashion SCRimmer and is only analog, 2 to 7.6 volts. Patch-boards for control of these were hard-wire or diode matrix. (Still have some of those, but the boards need to be calibrated to use them because of the diode voltage drop.)

 

[mstaylor]

The manual listed in Post #5 is for the SCRimmerette II. These do have a digital option. If your pack looks like the one in Post #1, then that is a good old fashion SCRimmer and is only analog, 2 to 7.6 volts. Patch-boards for control of these were hard-wire or diode matrix. (Still have some of those, but the boards need to be calibrated to use them because of the diode voltage drop.)

Thanks John, when he said he had one too I thought that was the one he was referencing.

 

[JerseyMatt]

Hi everyone! New here!

Sorry to bump such an old thread, but my community theater uses one of these antiques and we have a dimmer cartridge that went dead on us (both channels out, and the problem follows the cartridge into other slots). I had done some basic testing (looking for burnt components/open traces, trying to isolate parts common to both channels, etc) trying to get it working before our last show, but I didn't have much luck. I called a few places trying to locate diagnostic info, they told me to call other places, and then I was given Alan Child's number.. I spoke to him and he told me unfortunately he does not have any service data on these, nor does he have a test rig to do repairs.

I sort of shelved it for the time being, but now our next show is coming up in a month and I really need these channels working. So I went searching for more info and came across this thread..

Now our unit is slightly different. It does not have the center column of circuit breakers, and the cartridges are model TDI-D2 (not 3 as the OP has).. But I would imagine they have the same general principles in play.. Is the schematic going to be similar?

Right now I can not tell you if the test button lit up the light (I know I pressed the button, I just don't remember if it lit up). When I took it apart, some of the wire-to-board connections broke off, and I have to pull another cartridge to see where they go. BUT, while I was inspecting the board I noticed that the transformer secondary connection had two of the three (really short, really fine) enamel-coated wires broken off one terminal. In attempting to repair it I broke the last one. So off the bat I need to source a replacement transformer. Can you point me toward a compatible part number or at least a spec (I assume it's the same 12v as the OP's)?

If the transformer was not the original problem, am I correct to think that the same components can cause the same issue in this pack as what the OP had?

Also, I was under the impression that this was a 0-10v system.. I know someone mentioned that some are switchable.. Does that apply to the one I have? I was about to try something that was based on a 0-10v, but now I guess do I have to rethink it? What is the tolerance?

Thanks for any guidance you can give me!

 

[JD]

Would need pictures to tell if that's the case. If the transformer is open, then that will kill both channels. As far as I know, all the EDI of that era was 2 to 7.6 volts as compared to 0 to 10. You're not going to find a "drop in" transformer, unless it is off another unit. Just too many years out of production. But, from what I remember, pretty much any small 12 volt transformer will do. There is a lot of useful information on this thread, if it is the same unit. There was one "older" style that used pulse transformers but the board looked radically different.