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Durst M70 - bulb or transformer failing?

kal800

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Gdynia, Poland
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Hi,

Have a problem. When I switched on my enlarger, its lamp emited rather yellow tinted light and blinked. I was able to make it bright and constant after couple of switching on and off cycles, but the problem occurs.

What are the symptomps of burning out halogen bulb - should I order a new one, or rather check the transformer?
 
A halogen bulb is an incandescent bulb with a halogen gas added which increases filament life. https://en.wikipedia.org/wiki/Halogen_lamp
Like other incandescent bulbs, they pretty much work or not - nothing in between. It could be the transformer, but I would first check the switch and the lamp socket. Especially the socket. These wear and don't always make good contact with the lamp terminals. Do the easy/cheap stuff first!
 
Check the socket. Halogen lamp sockets are are renewable item.
 
I removed the bulb and saw some black something which I scrapped away, but the socket itself looks clean. I put the lamp back again and the flickering seemed to be less, however it is still dim, yellow and not constant - the effect as it wanted to get on the revs but cannot. The strange thing is that it worked for a while when I took it home.
 
Check the voltage at the lamp socket? Trace the wires back to the power source? Measure the voltage at the power source to the lamp?
 
Transformer is OK - it gives stable 13,65 AC current. Voltage at wires connecting to the lamp socket is something like 4V, but after some more measurements it dropped to 2,8V. While I do not have advanced electronic head for color printing, it seems something is with the circuit board (two small integrated units, couple of condensors and resistors) which probably adjusts the current based on signals from color head and probe unit. If I wanted to place my bet, I'd say it is one of the condensers...
 
kal800 said:
Stupid question - the lamp is fed by ac or dc current?
Click to expand...
The contacts inside the socket usually can't be seen. Most power supplies for enlargers provide AC. I don't have a manual for the M70 but the CLS70 is 12VAC
 

Hi,
The M70 was available with or without the stabilized PSU, it seems yours has it - as has mine. The Micro colour head is only connected bulb side so it can switch the lamp on and off, nothing more (apart from supplying it with power) - the big multi-way plug/socket visible when the colour/vario head is removed has a link to allow the bulb to work when other heads are used, all other connections come to it from the analyzer and don't connect into the lighting part.

Good news is the stabilizer could just be removed if it cant be fixed cheaply/easily, (Not really required for B&W) I recall somewhere having seen a diagram of how it is fitted as it was available as a user upgrade, I think it's a sticker inside the lamp-house unit.
 
4vac is not enough to fire up that lamp. Perhaps the wires are fried? The socket fried? But something between the bulb and your source is bad. I'd suspect bad solder joints or burnt wires. Trace the wires from the bulb to the source?
 
Solved! @Steve906 - you were right. I got rid of the stabilizer module - it required no soldering - just a matter of disconnecting three wires and connecting the bridge. I will handle the model to any local electrician to fix it.

Thanks for any help!
 

Hi,
Glad to be of help.
If you fix the stabilizer there is one thing to note in that there is quite a delay from turning on the AC wall power to the lamp lighting, maybe half a second or more, this can cause problems when doing test strips or short exposures. The delay problem may actually be less without the stabilizer, I've never tried. I have been planning on making a timer that uses the same low voltage side switching as the micro-colour head to see if that helps.

Steve.
 
You're right, I noticed that delay, but I presumed it is due to its developing malfunction. When I removed it, the lamp is on immediately. New electronic timers (like RH Design or alike) have ability to overcome that lag - you are simply setting a amount of time between the power on and actual time counting.
 
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