Omega Chromegatrol Problem

[amellice]

Hello, I've Omega D6 with its Chromegatrol. It was working fine, but after not using it for a couple of months, the timer/print switch doesn't seem to work. When I turn it on, the enlarger fan turns on immediately, but when I have it in focus mode, the enlarger doesn't emit light unless I wait for a minute or so. Then if I flip to print and flick Expose switch, nothing happens. Unfortunately, I'm not an electrician and I'm not sure how to resolve this problem.

 

[ic-racer]

Look for another one on ebay.

 

[Willyekerslike]

Hi amellice,

Have a look at Ollinger's web site and the following in particular

http://www.jollinger.com/photo/enlargers/chromegatrol_repair.html

 

[amellice]

Hi amellice,

Have a look at Ollinger's web site and the following in particular

http://www.jollinger.com/photo/enlargers/chromegatrol_repair.html

It seems that he had a similar problem but not the same, KHB offered to fix it which is great news

 

[Ian C]

This is the Omega 404-841 Solid State Voltage Stabilizer used with the Standard Power Supply to regulate the voltage. The Standard Power Supply is used with the Chromega D and E (5” x 7”) dichroic-filtered lamp houses.

https://www.ebay.com/itm/Solid-Stat...033172?hash=item5945bbed14:g:MlwAAOSwbn1eR3B3

The price is reasonable. I don’t know whether it is in working condition or not. You might want to wait until a nicer-looking unit is offered. There is some rust on the black enameled screw heads. This one might work perfectly. I simply can’t tell from the photo. The seller likely has no way of testing it.

I think that you should at least examine the photos to familiarize yourself with its appearance. This is needed with the standard power supply for color work. It is unnecessary for B&W.

The 6-bladed connector with non-conductive pilot pin (both male & female) is known as a Jones connector.

If you choose to get a Standard Power Supply and want to do color work with a Dichroic D or Dichroic E lamphouse, then you’ll want one of these.

The other alternative is to buy a used Sola CVS (constant-voltage transformer) rated at 250 va (volt-amps = watts). Then you’d have to have someone wire it for you. That’s a simple job, but requires knowledge.

Another possible alternative, is to bypass the timer circuit of your Chromegatrol. It is essentially a 120-volt 60-Hz constant-voltage transformer with an enlarger timer circuit. If the timer circuit could be bypassed, you could simply power the Dichroic D head with the Chromegatol and use an external timer. Some wiring might have to be altered, but I don’t know how to do that.

Your comment, “when I have it in focus mode, the enlarger doesn't emit light unless I wait for a minute or so.” makes me suspect the 4 microfarad 600-volt motor-run capacitor of the voltage-stabilizing tank circuit. If so, that’s great. This is easily tested, and easily replaced. This is capacitor C6 in the schematic (top version). It has clip-on leads, making it easy to change. These are used as motor-run capacitors in most applications making them not too hard to find. Like all electrolytic capacitors they are polarized, just like a car battery. They must be installed into the circuit in the correct orientation.

Don’t monkey with this yourself unless you have experience. A capacitor that size could knock you for a loop if you inadvertently become part of the circuit if It’s holding a charge. You should be able to find someone to test it and replace it if necessary. Please don’t buy one unless you’re certain that the one you have tests bad.

Capacitor C6 is on the left side of the schematic connected to an isolated set of windings about the transformer core. The capacitor and windings are known as a ferro-resonant “tank circuit” and is responsible for the voltage regulation. The transformer and tank circuit together are known as a constant-voltage transformer.

Here’s one. It has a slightly higher voltage rating (good) and has the clip-on leads like the original, $24 and free shipping. Some are priced up to $100—a ripoff.

https://www.amazon.com/Capacitor-Ca...7NVSVYX6JKJ&psc=1&refRID=ZY9EE7QVT7NVSVYX6JKJ

 

[koraks]

Like all electrolytic capacitors they are polarized, just like a car battery.

No, a motor-run capacitor is not polarized as it's for AC applications. So orientation doesn't matter. It's a good guess to start looking there, though. But given that a schematic is available, doing some measurements particularly on the power supply of the timer circuit would be the first step I'd take. It's entirely possible that e.g. C2 has died, which could leave the timer/relay circuit unpowered.

 

[Ian C]

The comments in post #6 above made me look again. There are no polarity markings near the terminals of C1 as I view the top of the capacitor in my Chromegatrol. I was told it was electrolytic years ago. That was apparently in error. Now I know better. Thanks for catching that.

The schematic shows a + sign along one lead of capacitors C1 and C2 indicating that they are electrolytic. Capacitors C3, C4, C5, and C6 lack a polarity designation, and so, are non-electrolytic.

http://www.jollinger.com/photo/cam-coll/manuals/enlargers/omega/chromegatrol-schema.jpg

I assisted Paul, a friend with a dead Vivitar VI about 1996 or so. He’d left it on in “focus” mode and forgot it. Several days later, he discovered it still on, but giving no light. The large aluminum-can type capacitor in the power supply had overheated making the oil inside expand and damaging the seal. The oil leaked out and made quite a mess. He cleaned the outside of the capacitor and we took it to Grainger Industrial Supplies for a replacement. I think it was about $7 at that time.

Paul installed the new capacitor and switched the timer to “Focus”. The lamp lit and everything worked normally. The last I heard, the Vivitar VI was still working normally. This was in the voltage-stabilized power supply, which I think, was a constant-voltage transformer, as is the Chromegatrol, but without the Chromegatrol's built-in timer.

 

[koraks]

Well, don't blame yourself Ian, the schematic is just confusing in this respect. All caps are drawn as electrolytics, while only some of them are. Your observation that C1 & C2 are electrolytics and the others are non-polar is consistent with how I read the schematic.
I would recommend replacing both C1 and C2 as they are likely not in good condition anymore. Electrolytics don't live forever and often have to be replaced after 15-20 years. C1 in the schematic is rather critical because it's part of the RC network that determines the time constant for the LM322. I wouldn't be surprised that in these boxes, if all components are original, the 'seconds' are in fact significantly shorter than actual seconds. Additionally, C2 is critical in smoothing the supply voltage for the timer circuit. As I pointed out above, its failure may lead to the problems outlined by the OP.

Likewise, CR5, a 1n4752 zener diode limiting the timer supply voltage at 33V, is also critical. Personally I find this approach towards a power supply for the timer circuit rather unfortunate as under certain conditions, the zener diode is actually pushed significantly beyond its maximum power rating. If it fails open, it will blow up the timer circuit involving a real fire risk.

Furthermore, it seems that the timer circuit is powered directly from the input AC without galvanic separation, which is from a safety standpoint again a suboptimal approach (to put it mildly), but functional as long as it is guaranteed that the circuit is electrically isolated from the user under any and all circumstances (which is in fact a little tricky in a darkroom setup where there's inevitably water around).

The exact purpose of running capacitor C6 is not entirely clear to me; it could be there for light temperature stability reasons, effectively smoothing the AC somewhat, or maybe protecting against momentary voltage surges. If it is suspect, I would be inclined to simply disconnect it (not short it!) and verify if the circuit works that way. If so, it can be replaced to bring the circuit back to its original design state.

Frankly, looking at this schematic, I'd be very much inclined to just run the fan from a 1:1 isolation transformer and replace the timer/switch circuit with a modern digital timer and discard the fundamentally compromised original circuitry.

 

[Ian C]

Capacitor C6 and the windings it’s connected to form a ferro-resonant “tank circuit” making this a constant-voltage transformer. This is a simple—no moving parts—voltage stabilizer. It’s an old idea, but still works well in some applications, such as color photo enlarging.

See Constant Voltage Transformer in the following articles:

https://en.wikipedia.org/wiki/Voltage_regulator

https://ustpower.com/comparing-auto...guide-constant-voltage-transformer-operation/

I have discussed with the OP the possibility of using the Omega D 412-020 Standard Power Supply. It is a 120 vac to 22.5 vac step-down transformer (same values as the Chromegatrol) with dedicated 6-blade single round pilot pin Jones connector that can be used directly with the Chromega Dichroic D lamphouse. It also accepts the 404-841 voltage stabilizer shown above in post 5 to keep the voltage to the lamp stable for color work.

 

[ic-racer]

Just checking in. Find a new unit yet?

 

[Larry Weaver]

Hi. I know this particular post is aging a bit, but it seems like the right topic and spot for a data dump.
In an earlier post (and many other threads) there was the normal question about exactly HOW or where to wire a regular timer into a Chromegatrol.
Many of you have been really helpful to me on this very subject. I completed a written description of the changes I made, and I updated the schematics with the wire color codes, and put in a photo or two, and some terminal numbers. Stuck it in the PDF file here. So I am hoping that anybody who wants to repair their Chromegatrol, or have it repaired locally, or just bypass the timer will find this info specific enough to be useful. Thanks a million!
LW

 

[choiliefan]

First thing I'd do is clean the contacts in the switches to eliminate a possible cause. These contacts are brass and develop a waxy green goo from oxidation and age. Perhaps some tuner cleaner will fix this problem.