Troubleshooting Durst CLS-301 Blowing ELH Bulbs

[jbmia]

Hi Folks,

Long time no post.

Having been side tracked with other activities and other gear, I have to admit I've neglected by Durst 138/139 CLS-301 combo. However, recently I came across some old 1920's 5x7 negs of local historical content (nostalgic old S. Florida), which I've cleaned up a bit and after a bit of dusting off the enlarger, baseboard, carrier, etc, I placed it into the negative carrier and proceeded to take a measurement with the Zonemaster II... then.. pop.. lights out. Somewhat quickly realizing that when one bulb blows both do, I replaced the ELH and seconds to a minute later, pop, another blew. Seems like alternatively on both sides. I went through 4 or 5 bulbs before realizing it was time to just stop, pull the CLS 301 off and put the condenser head back on. Never had an issue with the rig in the past.

For what's worth I have a complete back up unit and while it didn't blow bulbs on head #1, one side is entirely dark (unpowered)... I also tried the first power supply, #1, with the other head, #2, and it blew both bulbs in short order, so there are definitely issues with both powers supplies.

Questions:

- any ideas on what components of the EST-301 power supply (#1 blowing bulbs) might be causing the issue? The ELH is 120V / 300w so I'm guessing it's function is just power conditioning and on/off function only.. no voltage conversion...
- any suggestions on repair? I did ping Kevin at KHB, but haven't received a reply yet. Would be curious if anyone has any other service technician recommendations?
- Given the EST-301 was out of service for awhile, should I have brought it up slowly on a variac (like is done with vintage audio gear) ?

I know we have some very experienced folks on the forum here, so I appreciate any and all construction comments.

In the meantime, I've dusted off an old Sylvania #302 and I'm waiting on delivery of a 110/220 step up/down converter so I can use the LaFan with the Condenser head/#302 bulb.

Many thanks,

John

[ic-racer]

I have had good success replacing the sockets. If there is poor contact, the Triac keeps ramping up the voltage, until it makes good contact and blows the lamp.

https://www.photrio.com/forum/thread...acement.85653/

[Drew Wiley]

Ditto. Look for the simplest potential issues first. Look for any corrosion or poor fit in the sockets, and replace both bulbs with new ones. Test your incoming power voltage with a good meter for any serious fluctuations. Power supplies are meant to handle such issues, but don't do it quite so well as the components age. (I wasn't amused when a bored teenager shotgunned our local power pole transformer a couple months ago and drove our line voltage briefy batty). I've fiddled around trying to salvage these old power supplies, but find it easier to retire the power supply, just split off the fan circuit and run it directly 240V with a footswitch, and run everything else straight 120 line voltage with a simple timing control. There is a bit of rewiring needed inside the colorhead box itself to accomplish this; but a basic continuity tester is all you need to trace the respective wires.

If you didn't pick up the clue already, CLS301 heads made for the US market do predominantly run on 115 voltage. It's stepped-down inside the power-supply itself, which is designed to be easily reconfigured internally and with respect to sockets for which country it will be used in. To my knowledge, these US colorheads don't need actual 240 voltage for anything other than the fan behind the mixing box and the little lights illuminating the CMY adjustment dials in the head itself. Even the motors on the chassis for focus and head height are 115V. Frankly, the "stabililzed power" coming out of the controller is not as tight as my ordinary voltage coming right out the wall socket (except for things like that shotgun incident). I have dedicated 240 as well as 120 lines in my lab building, with especially good wiring.

[jbmia]

Thanks for the replies guys. Will take a closer look at the sockets and attempting to measure voltage ... much appreciation.

[Drew Wiley]

Look for any corrosion in your primary wall sockets and cord plugs too. Been there, done that. It made a big difference, especially here in our marine climate, where everything copper, brass, or aluminum gets a lot of atmospheric punishment. Even the fog is salty. But many inland cities get the same torture due to industrial pollution, plenty of agricultural sources of it too.