gralab 555 question

[dfoo]

I just got a timer from ebay after my last one stopped working. It just arrived and I tried it out. The first thing I noticed was that the second counting LED was very very dim. Ok, not a big deal. But then when I tried outlet A it never goes off. It was two settings dim and on. Outlet B is on/off. Is that expected?

 

[Mike Kennedy]

I have the 451.There are 3 settings on the display switch.Dim,bright,off.

 

[dfoo]

I'm not talking about the display switch. I'm talking about outlet A. It never goes completely off. If I plug a light into it, the light is dim when "off" and full on when "on". Looking at the manual on the gralab site, this does not look correct.

 

[Mike Kennedy]

A quick Google check showed that there are 3 levels of light intensity on the 555.

 

[RH Designs]

Sounds like the relay on outlet A is faulty. Solid-state relays can be damaged by overload or power surges to a point where they no longer switch off fully, and I would guess that is the problem with yours. We use electro-mechanical relays which, perhaps surprisingly, we find to be much more reliable.

 

[dfoo]

A quick Google check showed that there are 3 levels of light intensity on the 555.

That refers to the display lights (ie: m:s:ss), not the outlet power.

 

[dfoo]

Sounds like the relay on outlet A is faulty. Solid-state relays can be damaged by overload or power surges to a point where they no longer switch off fully, and I would guess that is the problem with yours. We use electro-mechanical relays which, perhaps surprisingly, we find to be much more reliable.

Ok, I wonder how difficult that is for me to repair? Since outlet B still works, all is not lost, but still the situation is not ideal.

 

[RH Designs]

If you can get inside the case and know how to use a soldering iron, it shouldn't be too difficult providing parts are available (i.e. not a discontinued item).

 

[glbeas]

I would see about returning it before attempting a repair, unless the timer was advertised as defective.

 

[dfoo]

I contacted the seller and got a discount on the unit. Its not worth the shipping cost to return it.

 

[Nicholas Lindan]

I agree with Richard that the problem is most likely a defective triac or solid-state relay in the timer.

Triacs and their ilk don't have a place controlling incandescent lamps unless they are protected with extensive circuitry to guard them from the currents and voltage spikes that can occur when a light bulb blows out and creates a momentary short that pulls 20 amps or more.

However, you didn't mention the enlarger head you are using with the timer, and so there is another possibility ...

If you are using a head with electronic controls or a power supply/regulator there is a possibility that a protection circuit in the timer (called a 'snubber') is letting through enough current to partially trigger an opto-isolation relay in the head. If you are using a head with a plain-ole enlarger bulb like a PH212 this won't be the case, and the symptoms the timer is exhibiting show that it is indeed broke.

If you think snubber leakage current may be the cause, try plugging an ordinary lamp into the timer and see if exhibits the same behavior. If it works fine with an ordinary lamp then you will have to disable the timer's snubber circuit.

 

[dfoo]

I have a durst M601 (plain bulb). I tried both the enlarger and a lamp. Both are dim in the off position, and full on in the on position. I'll take a look inside tomorrow and see what I can find.

 

[dfoo]

I took the timer apart this morning. I ordered two replacements, a triac L6008L6 and the triac driver MOC 3041. Should be available in 2-3 days, total cost ~$5. I'll replace those two and see if it works!

 

[dfoo]

Just to wrap this up, I replaced the triac today, and it now works! The LED also fixed itself (I guess it was somehow caused by the bad triac also). I can't say I did a great job in the soldering since my solder sucker disappeared, but it does work! Fortunately, I didn't have to replace the triac driver, I don't think I could have de-soldered that.