Chromega Troubleshooting Help

[reasonsandreasons]

Hey, all. I recently purchased a beautiful Omega D5 that came with a slightly-less beautiful Chromegatrol power supply/timer unit. The unit worked fine to test the enlarger both at the seller's and at home, but very quickly stopped working. Weirdly it identifies itself as a 412-045, which is technically the 230v/50Hz international model, but it has a US plug and again, seemed to work fine on standard US voltage and frequency, at least for a little bit. Taking it apart, too, there is no second transformer, which seems to be the only difference between the two models, at least based on my reading of the schematics. I also verified that the lamp's filament looked good, and probed the lamp socket with my multimeter to make sure there wasn't 24 volts there. Still nothing.

So, figuring that it was a US model and the issue was definitely on the power supply side, I started to troubleshoot. The timers in these things seem to go bad a lot more frequently than the power supplies, so I started there. Based on my reading of the schematic, jumping the cables that connect pins 4 and 5 of the timer relay (or the connectors those pins attach to, E9 and E11) bypasses the timer circuit and powers the enlarger lamp directly from the transformer. Lo and behold, that worked! The lamp lit and I was already planning the Arduino-based timer circuit I could make if the original was too far gone. But it seemed to only work once--since then I haven't been able to get the enlarger lamp to light, even by bridging the same connectors again.

And so, at the end of my very limited solo troubleshooting abilities, I wanted to come here to ask if anyone else had any idea what might be wrong here. I know the simple and expedient answer is to buy a new one, but they're somewhat rare and somewhat expensive and most importantly composed on entirely off-the-shelf, through-hole components. I'd prefer to fix this one if at all possible, especially considering that there aren't too many more where this came from.

Anyway, any hints as to where to start with this? More than happy to take readings on my end and do what I can to verify hunches or ideas from folks. If it's useful, there's a high-res version of the schematic here. Thanks!

 

[shutterfinger]

I would start with replacing the lamp socket.

 

[reasonsandreasons]

I don't have a replacement on hand, but on that suggestion I opened up the enlarger head to get a look at the lamp connections themselves. It looks like across the two pins the lap socket connects to there's a constant 25.11 volts or so AC, which would indicate to me that it was indeed the socket (as the lamp is 24v). However, when I bridge those two pins with a spare bulb to confirm that the socket is the issue, the lamp won't light. Is there any squaring those two results?

 

[shutterfinger]

What is the condition of the wires within 1 inch of the socket, soft and flexible, discolored, hard?
What is the wattage of the bulb?

 

[reasonsandreasons]

The bulbs are both old stock Omega 471-029 rated for 22.5V. I've attached pictures of the cables, but they appear to be in good shape for the age. They're flexible, but they have acquired a memory over the years, if that makes sense.

 

[shutterfinger]

https://www.interlightus.com/light-bulb/OMEGA-471-029
24V, 250 Watt, 10.42 amps.
A single strand of wire will show community and voltage but it will not carry the current load.
The wires at the connectors, especially the black, look weak. The black looks burned. The socket has discoloration at the black wire contact.
1. repair or replace the socket and wires at the connectors.
2. burnish the contacts of any relays in the power supply and timer or replace the relays.
You may have to drill out rivets and cut relay cases open. Some relay cases are bonded at the base and can be pried open.

P.S.
Heat from the bulb will eventually weaken the metal in the socket contacts resulting in them not conducting current even if making solid contact. The indication of this is that the bulb burns out quickly.

 

[ic-racer]

Of course pictures will be helpful to know exactly what you have seeing as you think they labeled it wrong.

From what I recall the Chromegatrol had two differentl circuits. I think the older one is probably non-repairable. Since the the transformer works, just use that with an external timer. Re-wiring the Chromegatrol to be a standard Chromega power supply will be easier than repairing the timer circuit in the device. The voltage regulation is built in to the transformer (ferroresonant transformer) and not in the electronics,

 

[Neal]

Dear reasonsandreasons,

I was in a similar situation and solved it with a junk box relay, a cheap regulated power supply and transformer from ebay.

Good luck,

Neal Wydra

 

[Doremus Scudder]

Whatever you end up doing, make sure you power the cooling fan, either separately (then you need to remember to turn it on and off) or in conjunction with the lamp power. IIRC, it takes regular line voltage.

Doremus

 

[reasonsandreasons]

Thanks so much for all the help, folks. I think I have a working solution:

• I used some spade connectors and wire to make a semi-permanent bypass of the timer circuit, which leaves the timer intact but out of the loop. That way if I want to come back in the future and actually repair the timer I can, but for right now it works fine as a stabilized power supply that can be used with an external timer. (It also still provides line voltage to the head just fine, so I shouldn't have an issue with that, Doremus.)
  
• I replaced the enlarger bulb socket with a modern shielded replacement, and, which should hopefully improve longevity (though if this one lasted forty years I don't know how much of a concern that was in the first place). I'm now getting 25.11 volts AC to the socket, which is good, and should be sufficient to power the bulb.

The one issue I still have is that neither of my bulbs work despite having solid filaments, but I think that's the result of a bulb-side variation of the issue shuttlefinger discussed in his P.S., as there's some charring on the leads. I've ordered a replacement bulb, and unless something deeply weird is wrong I should have a working enlarger once it gets here. Once I confirm that I'll update this post with my results and some documentation on the timer bypass, which should hopefully help save a few of these from the trash. It's a $5 no-solder solution, thankfully, so it's very easy to implement.