Chromegatrol timing circuit repair

[pwadoc]

Hey all, I recently inherited a Chromegatrol (version 412-040) power supply and timer for Super Chromega D enlarger that is exhibiting the classic symptoms of a problem with the timing circuit: the enlarging bulb doesn't light and the unit emits a strange buzz. I opened the thing up and looked for obvious damage but it actually seems pretty clean inside. I ended up labeling all the connections and pulling the board so that I can check/replace all of the components (starting the with the big electrolytic capacitor), but I'm wondering if anyone who has done this repair has any suggestions for a specific culprit. I took a video of the behavior (http://ur.sine.com/temp/PXL_20210225_040409931.mp4) so you can see what's going on. I'm also puzzled about the big aluminum cylinder (in the bottom right of the first image) in the housing. Is it a relay? A giant capacitor? I think it's labeled on the schematic as DS1 and DS2 (never mind I realized these are the indicator lamps, so I have no idea where it is on the schematic), since I don't see anything else on there it could be, but the symbol is equally inscrutable. Any help or advice is appreciated!

 

[DWThomas]

The big can at the lower right looks like the connection end of a capacitor. A similar can appears in various equipment for starting or split phase running an AC motor. (I just replaced one in my 12" radial arm saw.) Since you mentioned buzzing, that cap could possibly be a culprit -- but I have no idea what the rest of your circuit looks like.

 

[pwadoc]

The big can at the lower right looks like the connection end of a capacitor. A similar can appears in various equipment for starting or split phase running an AC motor. (I just replaced one in my 12" radial arm saw.) Since you mentioned buzzing, that cap could possibly be a culprit -- but I have no idea what the rest of your circuit looks like.

Looking at the schematic (forgot to add that to the first post, should be there now) again, I think you're right. I missed the cap labeled C6. I've never seen one that size, but I'm gonna guess it's a #1 culprit for this type of failure. Thank you!

 

[DWThomas]

Looking at the schematic (forgot to add that to the first post, should be there now) again, I think you're right. I missed the cap labeled C6. I've never seen one that size, but I'm gonna guess it's a #1 culprit for this type of failure. Thank you!

Ah yeah, it appears that unit has a ferro-resonant constant voltage transformer which likely needs that cap working to operate. (My saw had both a start and a run cap and I got both off an Amazon merchant and replaced them for a total of about $23. The originals had 1973 date codes on them so I shan't complain!)

 

[pwadoc]

Ah yeah, it appears that unit has a ferro-resonant constant voltage transformer which likely needs that cap working to operate. (My saw had both a start and a run cap and I got both off an Amazon merchant and replaced them for a total of about $23. The originals had 1973 date codes on them so I shan't complain!)

Yeah, I think you're right. Also enjoying the complete lack of any isolation on a high voltage device intended to work around fluids.

 

[ic-racer]

You would not want an enlarger or its power source anywhere near fluids! The 'wet' side of a darkroom is traditionally separate in space from the 'dry' side.

 

[ic-racer]

To give you some encouragement to persist with your repairs. I made two of these D5500 power supply boards from ALL NEW parts. Including an integrated circuit that was available only from OMEGA (I bought the last ones they had). Yes, this was one of the most amazing things I have experienced. I called Omega Satter in 2009 and they had a box of UDN5714M (and integrated circuit unavailable anywhere) so I bought enough to fix two power supplies!
BTW; After replacing every component except the UDN5714M the power supplies were still non-functional, it was the UDN5714M that had failed in both.

Every component replaced with new, except the transformers an the R2 trimmer pot: