Chromega D Dichroic II overhaul

[Matthew Tapson]

I recently set up a small darkroom with a Focomat 1C and because I have major GAS and also shoot on Medium Format and a bit of 4x5 also picked up 2 Chromega D Dichroic IIs which I feel are quite rare in South Africa where I live and so I was happy to find them. I swapped one with my local camera store for a Canon A-1 plus some lenses and got it on a D5XL plus easel, Rodagon 50mm, El-Nikkor 80mm and Rodagon 105mm on a lens turret. The second one I paid a good price for, approx $150, and came on a D5500 but with no lenses or lens mounts. Both came with Chromegatrol power supplies. One had a D-D mixing box and the other a D-B mixing box so that's great. Interestingly, the swapped one has a very high serial number - 835 527 - but is in a much worse condition than the other which has a very low serial number - 57 627 - and is in very good condition, and also has black housing instead of the silver of the younger one. Unfortunately the younger one has two broken dichroic filters. It is also packed with dust, grime and grease. But both of them have very stiff filter adjustment wheels, so naturally I want to service the mechanisms. I haven't found any guides online showing how to do this so I thought I'd log my process here in case someone else finds themselves needing to do it.

I've started with the younger one as a practice run for the older one and it's really not too complicated. Here are some pics of the gear.



The two chassis. The D5 is in better mechanical condition, so with the lens mounts I'll also clean this one up. But would love to hear about the relative merits of the two - I can't find that much info comparing them.



The broken cyan filter. The Magenta has actually fallen out of the assembly and cracked in half.



This is what the mechanism looks like. No wonder it sticks.

I'll post some more pics as I clean and reassemble and possibly a diagram showing the general layout of the parts.

 

[ic-racer]

You probably know this but take careful notes of the placement of the washers and springs on the filter mechanism.

 

[Matthew Tapson]

You probably know this but take careful notes of the placement of the washers and springs on the filter mechanism.

Thanks your posts have been some of the few responses on this topic. Sounds like you've refurbed a few?

 

[Neal]

Please post photos of your progress. I love to see old enlargers renewed.

 

[Matthew Tapson]

Please post photos of your progress. I love to see old enlargers renewed.

Will do!

 

[ic-racer]

Thanks your posts have been some of the few responses on this topic. Sounds like you've refurbed a few?

This picture is dated 2009, so it has been a while. Those three long black springs all have to be in the right position. I believe there were spacers between the moving filter arms and they have to be spaced just right so the black lever arms sit right on the cams. Might be a good idea to replace th lamp socket too.

 

[Matthew Tapson]

Dismantling the enlarger head starts with removing both side covers. After pulling the lever that switches between white and filtered light, there are 4 screws in the corners of the sides that hold them on. The two Philips screws in the middle of the covers are for adjusting the position of the mounting thumbscrews, presumably for alignment, and don't need to be removed. The thumbscrews need to be removed as well. There is an extruded aluminium spar that forms the main structural support of the enlarger on the front top edge. On the back side is an assembly of the back plate with the cooling fan, the electrical connectors and the compartment that houses the lamp, a heat shield and the filter adjustment mechanism. As the spar is held in place by two of the cover screws it will be loose so remove the plate holding the fan, and note and disconnect the electrical connectors. I disconnected the lamp at this point, probably should have been done first. Take lots of photos as you go.


Side cover. This lever shifts the entire filter assembly into and out of the path of the light and also moves the scrim into the light path at its third position.


These screws release the back cover of the enlarger.


Here is a pic the connector layout.

 

[Matthew Tapson]

After disconnecting all the wires the plate holding the fan can be set aside. There is a piece of frame that this is connected to which runs the width of the enlarger, and this is also screwed to the vertical divider that the filter assemblies are attached to. The assemblies each have a spring - take a pic of where these are connected and disconnect them. I use a small pin that I have bent into a hook for small springs. After this, look for the screws that are on the opposite side of the vertical plate and which are screwed into the back of the brass spacer. These were tight so I used a spanner on the brass spacer to loosen the screws. Once they are loose, the whole filter assembly comes out.

 

[Matthew Tapson]

You can now remove the bottom cover of the enlarger by removing three screws. Don't remove the silver recessed screw at this point.



I now freed the heat shield behind the bulb that lights up the white/high/low indicator and the bulb itself and unscrewed and freed the profiled heat shield that sits between the main lamp and the dials for the filter adjusters.



The second one was stuck to the light seal foam strip so I damaged that seal but will replace all the light seals that seem worn out.

 

[Matthew Tapson]

We've now accessed the filter adjustment mechanism which needs to be stripped. On this first enlarger, it was binding on the shaft the wheels sit on due to all the old dried out grease, but the filter assemblies themselves were also binding on the brass rods that they are hinged on. So we will need to remove all the old grease and regrease these mechanisms. There is a specific arrangement of snap rings, washers and spring washers that I have made a layout diagram for. This diagram is proportionally correct. The only thing I have left out is the plastic bushes that seat the wheels on the shafts but this shows the arrangements of washers etc and the shafts themselves. Each cam is fixed to a shaft, the outer cam is on the longest and thinnest shaft and then the other two are on hollow brass shafts that sit one inside the other.





One thing I did, was note that alignment of the cams at a specific position - 000 for me. I drew a line across them and one on the metal behind. However, knowing I was going to use solvent on these I then scratched a mark into the outer cam in line with the black mark - similar to how you'd mark helicoid positions if taking a lens apart. The three cams can be aligned to each other by sticking something through the holes in the front so only the outer cam needs to be marked like this.

 

[Matthew Tapson]

The process of taking this lot apart entails removing the snaprings starting on the opposite end to the cams. I started by removing the mechanism the outside lever controls.



Take note of how the wheels are aligned to the values on the counters. There are hard stops at 000 and 170. The stop is a raised portion of the wheel that butts against a small post that you can see in this image below. I don't think that you need to preset this in any specific way, but I chose to set all the counters to zero before loosening off the blind nuts on the collars of the thumb adjustment wheels.

Now you can undo that recessed silver screw and remove the counter mechanism.



In this pic you can see the first set of spring washer/washer/snapring to the right of the support column thing. There are two of these columns which can be unscrewed now. Take photos of everything. To the left of each column is a snapring/washer (in this visual order).

As your release each snapring set, the shafts will be released and you can slide them out as this happens. Arrange your parts nicely like below and take photos the whole way so you can put everything back in the right order.

 

[Matthew Tapson]

That's the disassembly done on that part. Next up is cleaning everything. I had benzene handy so used that to clean all the old grease off everything. There was some minor corrosion in places like the brass shafts too that I used 1500 grit wet/dry sandpaper to clean up. I banged the adjustment wheels in my ultrasonic cleaner. I was very careful with the fragile looking plastic bushings. I imagine if these break or crack it would be a problem. After thoroughly cleaning off the shafts and cams and wheels, I disassembled the filter assemblies and scrubbed those down too. I was careful not to touch the filters themselves but did rinse the whole lot under warm water after cleaning off the dried grease.

 

[ic-racer]

I'd try to glue those filters back together. Unless you have found new ones?

You could add black pigment to epoxy so no light peeks through the cracks or missing pieces.

 

[ic-racer]

BTW: excellent job. There is no service manual, so far this thread is the next best thing.

 

[Neal]

Good stuff!

 

[Matthew Tapson]

I'd try to glue those filters back together. Unless you have found new ones?

You could add black pigment to epoxy so no light peeks through the cracks or missing pieces.

No, I haven’t found new ones. I didn’t consider gluing these though, that would definitely be worth a try. Thanks for the tip I was thinking it might end up being just a non filtered head, with a filter holder underneath. But first prize is definitely getting it fully fixed.

There was a bunch of glass from a lamp inside the enlarger so I have a feeling when the lamp exploded a piece of glass damaged the badly cracked filter. Just a theory though

 

[aconbere]

No, I haven’t found new ones. I didn’t consider gluing these though, that would definitely be worth a try. Thanks for the tip I was thinking it might end up being just a non filtered head, with a filter holder underneath. But first prize is definitely getting it fully fixed.

There was a bunch of glass from a lamp inside the enlarger so I have a feeling when the lamp exploded a piece of glass damaged the badly cracked filter. Just a theory though

I found a few filters on ebay recently, only picked up a magenta. I think with a little patience you’ll find them for not too much.

 

[Matthew Tapson]

BTW: excellent job. There is no service manual, so far this thread is the next best thing.

Thanks, I enjoy taking things apart

 

[Matthew Tapson]

I found a few filters on ebay recently, only picked up a magenta. I think with a little patience you’ll find them for not too much.

Ooh, good idea. I’ll keep an eye on that.

 

[Matthew Tapson]

I decided to start stripping down the second enlarger. I basically followed the same steps and it took just a few minutes to get to the filter wheels again. Here is the assembly from the second enlarger which is like chalk and cheese compared to the other one. I was almost tempted not to strip it but the Cyan (I think) wheel on the left was quite stiff so I went ahead and found the same sort of dried sticky grease inside.



I cleaned up all these parts and then started to reassemble the first enlarger again. I use Molybdenum grease for photographic stuff - this tube is from Tamiya. I have to say that working with Snaprings is an exercise in frustration. Combined with the spring washers that frustration is drastically heightened. Trying to compress the springs and get the snaprings into their grooves with only two hands took a while but I got it done with the only damage being to my fingers. Doing the second one was not quicker or simpler and I damaged the same spot on my finger again in the exact same way. I'm sure there is quite a basic spring washer compresser that slips over the mechanism and makes this process much easier. Anyway, both filter adjustment mechanisms are lubricated and reassembled and seem to be working smoothly. I'll do the filters next, probably tomorrow and then hopefully reassemble the rest of the enlarger quite quickly.

 

[aconbere]

You’ve almost got me thinking I should strip mine for a quick clean. Mostly my gears all move smoothly but they’re a little bit funky. The far left when moved likes to transfer adjustment to the filter next to it, and all of them are a bit sloppy.

A minor annoyance but it would make working in the dark room a smidge more comfortable.

 

[Matthew Tapson]

Yep that transfer was happening between the first two on my first re-assembly too. I think it’s due to the middle shaft binding to the outside shaft ie lube is dry - I think I didn’t use enough grease on the plastic bushes. It’s not too much of a mission to do the service and fun getting to know the machine. There’s a chance you’ll need to replace some light seal strips - I found a kind of self adhesive felt pad at the hardware store that I will use.

 

[aconbere]

Yep that transfer was happening between the first two on my first re-assembly too. I think it’s due to the middle shaft binding to the outside shaft ie lube is dry - I think I didn’t use enough. It’s not too much of a mission to do the service and fun getting to know the machine. There’s a chance you’ll need to replace some light seal strips - I found a kind of self adhesive felt pad at the hardware store that I will use.

I have so many light sealing materials from camera repair already.

 

[axestrata]

as a novice, working with snaprings and spring washers is simply maddening. Anyway, incredible work!

 

[Matthew Tapson]

as a novice, working with snaprings and spring washers is simply maddening. Anyway, incredible work!

Thanks!