Omega D5500: How to Set Color Probe Offset

[ic-racer]

The service manual for the D5500 does not do a good job of describing the 'Offset' adjustment for the color probe.

COLOR PROBE: This is the small box attached to the light box with 4 screws. It has 3 sensors to monitor the color of the interior of the mixing box. There is a cable that connects the color probe to the power supply. There are six adjustment trimmers on the color probe. Three are visible and adjustable from the outside (the Gain adjustments) and 3 are only visible by removing the color probe (the Offset adjustments).

SYMPTOMS: On my units that were found to have maladjusted offsets, the head would 'hunt' for the correct value. Sometimes a filter would slowly cycle up and down during the exposure. Extensive troubleshooting isolated this type of problem to the color probe adjustment.

FIRST: The color probe gain setting is accurately detailed in the manual. This adjustment is carried out with the 3 trimmers accessible from the outside of the color probe. Before adjusting the 'Offset,' adjust the color probe gain, per the manual.

PROBE REMOVAL: To get to the 3 adjustment trimmers for the 'Offset' you need to remove the 4 screws and remove the cable. Be careful of the little UV filter. It is not affixed to anything and it could fall on the ground and crack if you are not careful. The UV filter is sandwiched between the photodiodes on the color probe's PC board and the housing of the mixing box.

PREPARE: You will use a DC millivolt meter for the adjustment. The color probe needs to be plugged in to the power supply with the cord. A piece of black tape is placed over the 3 sensors. Light will still leak under the housing, so I do this in subdued light.

MEASURE: The enlarger power supply is turned on but the lamp does not need to be on. Measure between the indicated resistors and ground (the aluminum housing is ground).

RECOMMENDED VALUES: The manual asks for around +10 millivolts. In the probes that caused me difficulty, the potential had dropped below unity (to a negative voltage). In one mixing box (purchased brand-new from B&H) I found it was set to about +110mV. After some experimenting it seems any value between +10mV and +100mV yields the expected performance. However, should the offset drift to a negative number, then the system won't function correctly.

SETTING: Use the appropriate trimmer to adjust the millivolt offset of each channel to the recommended value. (+10mV, if going by the manual).

FINISH: When done, package the probe back on the mixing box, making sure the little UV filter sits over the 3 sensors.

The following picture shows the color probe after removal from the mixing box. The measurement points are indicated in the photograph.

 

[BobNewYork]

Would the fact that the internal trimmers are off result in rapid shifting of the reading for the external ones? E.g. I would find that all three colours would go from 0 to +- over 25 in a matter of days and require adjustment of the external pots.

Bob H

 

[ic-racer]

I have a hunch. When I was evaluating my five color probes and mixing boxes I came across at least one little offset trimmer that caused the values to jump all over the place when I adjusted it. It only occurred to me later that the was probably a 'scratchy' pot that may benefit from some DeOxit or even replacement.

So, when I was checking over my probes' circuit boards I went through this list:
Resistors = Stable values
Wratten Filters = Stable
Photodiodes = Stable
ICs = Stable
Color of the inner styrofoam = Stable
Connectors = Clean, low resistance
Power Supply Voltage to the Probe = Stable
Trimmers = Potential for unstable values.

 

[ic-racer]

I am continuing my exploration of the color probes and mixing boxes.

I won't even get in to any discussion about the possibility of dichroic filters fading, but between all my enlargers, there were differences in the maximum coloration that the system could set. According to the manual, between 199 and 175 is normal. Just by looking at all my dichroic filters in three heads I can say that I see no visual differences in the dichroic filters.

I think there is no question that Wratten filters can fade, so I checked all the little Wratten filters that cover the photodiodes. Sure enough, there were some differences.

In the picture, the mixing box that the top set of filters came out of would only go to 150 Magenta. Whereas the bottom one would go to 199 Magenta. The projected color was the same in each case, but the system only reads 150 because the green filter has faded. In the system the lower the voltage the higher the CC of coloration read by the probe. So that faded green filter is letting extra light in, which raises the voltage reading of the green photodiode and thus the system thinks it is only getting 150cc.

 

[ic-racer]

That faded filter, though, isn't causing the intermittent issue with instability in the filter setting. I did confirm that when the system is 'unstable' the (yellow, in my case) gain setting value varies up and down. So, without touching the adjustment trimmer it varies between, say -25 and +25. The others are dead steady.

I tried using DeOxit on the two trimmers for the yellow channel, but, because of the trimmer design, I don't think any got in to the wiper.

I'm swapping between 4 mixing boxes, 4 color probes, 4 power supplies, 3 controllers and 3 heads. Because the instability seems to come-and-go, and the number of different combinations to try I have not isolated the problem to any single component yet.

 

[ic-racer]

I also duplicated a condition mentioned in another thread where someone posted that the motors would not stop in the WHITE setting. I may have a solution to that.
According to the manual, if the gain trimmers are set for too NEGATIVE a setting, the motors may not stop. So, I would propose that if the motors won't stop, try screwing the gain trimmers in all the way (to make a more positive gain setting).

 

[ic-racer]

Would the fact that the internal trimmers are off result in rapid shifting of the reading for the external ones? E.g. I would find that all three colours would go from 0 to +- over 25 in a matter of days and require adjustment of the external pots.

Bob H

After overhauling my five color probes and mixing boxes I am pretty sure all the problems I was having with unstable settings were related to one of the connectors between the color probe and the power supply. After treating with DeOxit all is well. All components checked out OK (except the Wratten filters).

 

[ic-racer]

Back to the faded filter problem.

After doing some research on the Wratten filters, it seem that the green filter they used in these color probes is NOT a "Special Dye" filter. This may be the reason the green filters have faded more than the others.

Omega D5500 Color Probe Green Filter = Wratten 99 (non-Special Dye)
Omega D5500 Color Probe Blue Filter = Wratten 47B (Special Dye)
Omega D5500 Color Probe Red Filter = Wratten 92 (Special Dye)

The Wratten 99 Green is like a 16 and 61. The 61 is available as a Special dye filter but the 16 is not.

 

[ic-racer]

BTW I did some experiments using various "Primary Green" Rosco filters I had laying around and the probe did not seem to function correctly, even after re-setting the white light gain.

So, this leads me to believe that an exact Wratten 99 is required for correct function.

My plan is to go ahead and get a Wratten 99. I will have plenty of material for my 3 heads and some left over.

So, I think the conclusion here is that for anyone with a D5500 that does not go to 199 on the Magenta channel, I'd replace the Green Wratten 99 in the color probe before considering replacing the Dichroic Magenta filter. Also, the Green Wratten may need to be replaced on a regular basis for normal function (since it is not a Special Dye filter).

As a side note, it seems the little filters are just about the size that a standard office hole-punch creates.

I'll be glad to send out a little disk of fresh Wratten 99 to the first 3 people that contact me (continental USA please).

 

[ic-racer]

Sometimes you are lucky...

On a whim I checked my local photo shop and they had a new 3 inch Wratten #99 in the 'bargain bin' for $16 UDS. Not bad

 

[BradS]

Thanks for posting these two thread on the maintenace and service of the Omega D5500. They're both very interesting and helpful.

 

[ic-racer]

Got the new Wratten filters in place in the color probes that needed them and now all my color probes show 199M when the Magenta filter is all the way covering the light path.

Next...I just completed a transaction for a new old-stock push-button keyboard conversion kit for the CLS controller (429-931). I guess they had problems with the membrane keypads, thus the need for the conversion kit. One of my membrane pads is pretty worn and has some cracks on the surface. That controller will get the new keypad. I'll post the conversion when the parts come.

 

[ic-racer]

Making the new Wratten filter disk for the color probe sensor.