Jobo LPL 7415 power supply issue, lightbulb keep burning.

[Jeremy Saint-Peyre]

Hello guys and gals,

I just got a Jobo LPL 7415 (and roughtly a complete lab) for 500$.

I keep having a major issue, each time i'm putting the timer switch on, the lightbulb burn... a quick flash and nothing.

Here is how it is build, i hope someone can help me out, i suck at "electrical engineering". The power supply fuse is good, i feel there is something weird with the power supply. I made a connection diagram, it's all the way down the post.

So, the light bulb and the cooling fan (the fan is behind the circle shaped piece) cable are linked between the enlarger and the power supply through the same cable :

Until there, nothing weird. On the other face of the power supply : the grey cable is the fan cable, (the white cable is the lightbulb/timer cable) it is plugged in the domestic electric network, as specified by the user guide, because the fan must be running at all time. When i turn the power supply ON, the fan work perfectly.

Now, the lightbulb/timer part : it is the white cable, but it need an other cable (a standard alimentation cable a grabbed) to allow it to be plugged into the timer :

then you can plug it into the timer :

Then i plugged the timer on the same power strip i plugged the power supply, lifted the timer switch and the lightbulb burnt.

here is how i plugged it all :

I don't get it, and i don't know it could be done an other way...

Thank you !

 

[AgX]

The circuitry is puzzling...

-) the English manual shows a power supply with only 2 cable connections (to the enlarger and to the mains)
-) your power supply seems european (german made housing), it got 3 cable connections
-) your sketch shows 4 cable connections at the power supply

 

[Jeremy Saint-Peyre]

- Yes, i got the english manual too, they say that depending on the country, the power supply can be different.
- Yes it is european, Swiss to be acurate.
- Only three cable connection : the Enlarger -> Power supply fit both Fan/Lightbulb calbe inside one :

 

[shutterfinger]

I would suspect the mechanical switch in the timer that controls the light to be bad. Attach a volt meter to the light out to the power supply socket and turn the timer on, the meter should read the voltage necessary to trigger the power supply or the voltage the bulb requires. If the timer test good then the power supply should be suspect then the light socket itself.

 

[John Koehrer]

burning the bulb out as soon as the timer is actuated suggest too high a voltage to the lamp.
I would check the voltage to see the output. It should not be the same as the network(240/220?) Many
heads will have a low(75-80) voltage obviously it depends of the lamp.

So to high a voltage to the lamp from the timer so the timer's at fault or it may even be the wrong lamp.

 

[AgX]

burning the bulb out as soon as the timer is actuated suggest too high a voltage to the lamp.

I understand the OP that with "burn" he means the lamp flashes for a moment, not that it blows.

I would suspect the mechanical switch in the timer that controls the light to be bad.

Yes, a instable switch. A 2-state switch not holding the the on-state.
(Though I have never experienced such.)

 

[shutterfinger]

I've had switches that the operating lever of the timer would put slightly more pressure on the contacts at turn on but not hold enough pressure to make good contact and switch contacts that were burnt that would not conduct enough current to operate the lamp. There is also the possibility a relay is used and the hold circuit has failed.
There is the possibility that the timer is solid state and a SCR, transistor, or IC is at fault.

 

[Jeremy Saint-Peyre]

Hello, and thanks for getting back, so to clarify : the lightbulb do blow instantly. It did blow the 200W original lightbulb.

The power supply is supposed to lower the voltage so that the lightbulb don't blow right ?

I took a picture of the below of both the power supply and the timer if that help :

 

[AgX]

As I thought, the power supply is german... even quite recent (230V).
Its label got an error: it says for the sec. circuit 0.1A but instead it must be 10.5A (though that is of no concern for your issue).
Another puzzling thing is that the power output is rectified. To me it makes no sense to built a 250W rectifying stage if at best one needs DC voltage for just for a fan (which seems to be driven on the mains anway). Maybe another labelling error.


So you lost several lamps during your endeavours. Are you sure you got lamps of right voltage (24V) ??
The original one might have blown due to end of its lifetime, the others might be wrong ones.

 

[Ian C]

I presume that you meant that as soon as the current is applied to the lamp, it flashes brightly and the filament melts in a fraction of a second, destroying the lamp.

If so, then obviously the lamp is receiving far too much voltage. This assumes that the lamp is the one specified by the maker. I think this is the 200-watt 24-volt EJL (MR16 reflector, GX5.3 two-pin base).

From your description, it appears that the power supply has become defective and is delivering too much voltage to the lamp circuit. To remedy the situation, either the power supply must be repaired, or it must be replaced with another power supply of the correct specifications and in good working condition.

 

[AgX]

I assume the power supply still being of the classic transformer type. These practically only can deliver too high voltage in case of melted through isolation at the secondary coil. I expect even the rather high rated fuse at the the primary coil to prevent this. But I am no transformer specialist...

 

[Jeremy Saint-Peyre]

Hi again everyone !

So, AgX, i think you figured it out, both the lightbulbs i tested the enlarger with -as well as the lightbulb thas was used by the previous owner- are... 12V lightbulb. I guess the man probably had a temporary solution for 12V lightbulb. But the lab wasn't used for ten years and the photographer is dead, it was kind of messy so i may have let something pass through my "vigilance"

If the delivered electricity is twice as high, as Ian C told : the filament melts in a fraction of a second, destroying the lamp.

I'll try with a 24V lightbulb, if it still melt, i'll consider having the power supply fixed.

Thanks a lot for the help !

Any recomandations for that in Europe ?

Thoughs on a LED lightbulb ?

 

[Ian C]

Since you used 12-volt lamps, there is likely nothing wrong with the equipment. Rather, you simply used the wrong lamp. Install the correct 200-watt 24-volt EJL lamp and the enlarger should work properly.

It’s prudent to buy at least one extra lamp so that you’ll have a spare lamp on hand when needed.

It’s also good practice to install and remove the lamp 5 or 6 times in succession about once per year. This will lightly abrade any corrosion that might begin to form on the conductors of the lamp and socket. Any such corrosion acts as an INSULATOR, increasing resistance and compromising the current flow to the lamp.

 

[Jeremy Saint-Peyre]

Thanks Ian C, i'll do that !