Jobo LPL C7700 broken power supply

Synou · Sep 24, 2022

Good morning everyone!

So here is my issue today… I bought a Jobo C7700 enlarger to be able to print up to 6x7 medium format negatives.

I plugged the little guy in and was happy to see that it was turning on! But after about 30 seconds on “bulb/continuous” mode on the timer the enlarger turns off.

At first I blamed my timer but I tried on some other enlarger and it works fine.

I then blamed the power supply and looked for some bad contact inside but it seems fine… I’m at a loss and maybe wondering if I should try to make my own power supply? (Which I have no clue how to do haha)

Anyways, if any of you have some insights or know how to fix I’d be grateful!

Some infos:
Output from my plug in the wall is 230V (Netherlands)
Light bulb is: 12V 100W

Some photos of everything.

Thanks!

MattKing · Sep 24, 2022

Welcome to Photrio.
I added LPL to your thread title because that will be more easily recognized by many who are outside of Europe.
That is the correct bulb - has it by chance burned out?

Synou · Sep 24, 2022

MattKing said:
Welcome to Photrio.
I added LPL to your thread title because that will be more easily recognized by many who are outside of Europe.
That is the correct bulb - has it by chance burned out?

Thanks for the precision on the name and for your welcome!

Well I have to say I don’t know much about those Halogen light bulbs. Would it still turn on for a little while before dying again every time if it had burned out?

Every time I turn it on, it makes light for 30~45 seconds then turns off. And I have to wait about 2~3 minutes before I can turn it on again. If that’s a normal « dying bulb » behavior then I’ll buy a new one!

AgX · Sep 24, 2022

The power supply is made for 220V, thus delivering now nominally 5% higher voltage to the lamp (if its output is not regulated).
This basically is a point to consider.
But your model is a regulated one.

Howeever this is not to explain what you experience and which also has nothing to do with the lamp.

It rather makes me think of a safety thermo-switch going into action, in one of the appliances.

Synou · Sep 24, 2022

AgX said:
The power supply is made for 220V, thus delivering now nominally 5% higher voltage to the lamp (if its output is not regulated).
This basically is a point to consider.

Howeever this is not to explain what you experience and which also has nothing to do with the lamp.

It rather makes me think of a safety thermo-switch going into action, in one of the appliances.

Thanks for your insight! Yes the output voltage in the Netherlands is 230V, I didn't think it could cause a problem... And I definitely don't know how to fix it. If it's a thermo-switch I have no clue where to look haha

I was thinking of making a brand new power supply with a new transformer, but I can't find a 230V to 12V 100W AC transformer. (To my understanding it is what I would need).

AgX · Sep 24, 2022

Such voltage difference at the output will reduce the lifetime of your lamp, but others lived well with these old power supplies, maybe yours is even regulated than there will be no problem at all. (A unregulated supply would only contain a transformer and at best a switch and a fuse.)

Synou · Sep 24, 2022

AgX said:
Such voltage difference at the output will reduce the lifetime of your lamp, but others lived well with these old power supplies, maybe yours is even regulated than there will be no problem at all. (A unregulated supply would only contain a transformer and at best a switch and a fuse.)

So you think my best bet would be to change the light bulb before trying to change the power supply?

AgX · Sep 24, 2022

The other way round... What you experienced cannot be explained with any incandescent lamp.
(In theory it even may be a loose wire connection at the lamp socket. So you might check the lamp's feet and the wires at the socket.)

My first aproach would be checking the rest of the installation for a thermo-switch or electronics running havoc.
You already checked the timer at a different enlarger which most likely excludes it as culprit.

brbo · Sep 25, 2022

My LPL C7700 came without a power supply. I’m using it with a power supply taken from an old PC (personal computer).

MattKing · Sep 25, 2022

My LPL 7700 enlargers both came with LPL labelled power supplies (designed for US and Canada).
The 220 version of that power supply available through KHB, the Canadian distributor, is pictured here on KHB's website:

Obviously that at least looks very different from the one that Synou has.
Is there a possibility that the one that Synou has isn't well matched to the enlarger?

AgX · Sep 25, 2022

The one in question is a german-made, regulated one.

I have not even read in german literature of LPL enlargers, I only know them from two of the Jobo catalogs.
So I guess the market was small. Maybe LPL did not bother to offer a dedicated power supply or for whatever reason Jobo decided to supply such theirselves.

From the indicated data it is a perfect match.

I would disconnect the four wires to the electronic board and instead reconnect them so that the transformer is connected to the mains just via the switch and the fuse.

There is quite a chance that then the system would work fine. Though from a glance at that board there is nothing irregular.
In Germany, at least where I live, we still(!) got a very stable net and unless the OP is located in a industrial zone or so, he likely wil not need the regulator board.

In case that is the solution and the OP got an electronics tinkerer/expert at hand he may have him look at that board to find the fault.

Synou · Sep 25, 2022

brbo said:
My LPL C7700 came without a power supply. I’m using it with a power supply taken from an old PC (personal computer).

Oh I’m curious on how this works! Did you use a transformer after the power supply? If you have some photos or more details I’d be interested!

brbo · Sep 25, 2022

All ATX power supplies have 12V rail, so you don't need anything else. There are a number of guides on the net that walk you through it if you are as electro-illiterate as I am. A 300W ATX supply should be enough for this enlarger, but you should check the specs.

Even if you don't have an old PC lying around somewhere, getting a used PC power supply or even a new one should be very cheap compared to buying the OEM part. The PC power supply will probably have a fan (fanless are more expensive), but mine is very quiet and introduces no vibrations...

AgX · Sep 25, 2022

But there is no sense in looking for a switching DC power supply or a new transformer als long the OP still got an apt one at hand which he did not try yet.

Synou · Sep 25, 2022

AgX said:
The one in question is a german-made, regulated one.

I have not even read in german literature of LPL enlargers, I only know them from two of the Jobo catalogs.
So I guess the market was small. Maybe LPL did not bother to offer a dedicated power supply or for whatever reason Jobo decided to supply such theirselves.

From the indicated data it is a perfect match.

I would disconnect the four wires to the electronic board and instead reconnect them so that the transformer is connected to the mains just via the switch and the fuse.

There is quite a chance that then the system would work fine. Though from a glance at that board there is nothing irregular.
In Germany, at least where I live, we still(!) got a very stable net and unless the OP is located in a industrial zone or so, he likely wil not need the regulator board.

In case that is the solution and the OP got an electronics tinkerer/expert at hand he may have him look at that board to find the fault.

So you are suggesting that I try bypassing the green pcb or the big brown rectangle? I’m sorry to be so slow at understanding recommendations haha, but I really can’t find what is wrong with my power supply…

Isn’t the green pcb what makes my output 12V? I have no idea what is the purpose of the brown block.

AgX · Sep 25, 2022

The "big brown rectangle" is the transformer. This one should be active. The "green pcb" is the voltage regulator. This may be the culprit and thus should be bypassed.

The transformer changes the incoming 220V AC into 12V AC. Actually, on its own now 230V AC into 12.6V AC.

The added regulator checks the incoming voltage for deviation and regulates it before entering the transformer. So that it always gets its 220V AC ad puts out that 12V AC, even today at the higher mains voltage.

Now I feel bad that I proposed this modification as I fear you could kill yourself in the event.
Maybe others chime in in this matter.

Synou · Sep 25, 2022

AgX said:
The transformer changes the incoming 220V AC into 12V AC. Actually, on its own now 230V AC into 12.6V AC.

The added regulator checks the incoming voltage for deviation and regulates it before entering the transformer. So that it always gets its 220V AC ad puts out that 12V AC, even today at the higher mains voltage.

Now I feel bad that I proposed this modification as I fear you could kill yourself in the event.
Maybe others chime in in this matter.

Don’t worry, I have some little experience with soldering and handling electrical components, I’ll be extremely careful if I do go this route. Would it be wise to try to find a new regulator and solder it in place of the old one? Would it be easy to find a new regulator?

AgX · Sep 25, 2022

First check if the system works without the regulator. To me it seems the best candidate for being the culprit, but I am no electronics expert to say for sure.

If it works then be aware that the lamp will run at higher temperature (less reddish) and with reduced lifetime. To what extent one hardly can say without knowing the actual output or rather input at the socket.
Then be alert on any voltage variations at your net. As said I do not got such. If you got such the stable periods should at average at least be long enough to do all metering and the exposing of a a print.

Then you could decide whether you need a regulator at all, and then whether to have yours repaired, to buy a readymade module with apt characteristics (whatever they be), or to skip the tranformer approach at all and go the switching power supply way, for instance with a desktop-computer power-supply.

Jobo LPL C7700 broken power supply

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