Warning: strobe lights should be handled and repaired by professionals only. Inside the light, circuits store high voltage which can cause fatal injury if not handled properly. Even after unplugging, there is high voltage present, so I request not to fiddle with these lights if you are not qualified to do these kind of repair jobs. Information provided below is only for learning purpose. I take no responsibility if you hurt/kill yourself while trying to repair these lights.
The strobe light we are going to repair in this article is an electronic light called Pronlinchrom 23 (not digital) and is very popular model used in studios for taking photographs. These lights after extensive use may stop working because of wearing out of some of their internal components. Main causes of failure of these lights are high temperature and high voltage.
When a strobe light stops flashing, first thing to check is the power cord and then the filament for any kind of damage. If both of them are fine then it’s time to open up the unit and check its internal components for any faults. Before you unscrew it to open, beware that capacitors inside the light have very high voltage present even after you have unplugged it and it can give you a lethal shock. So what you can do is either leave the lights unplugged for whole night to discharge itself and do the repairs next day. If you don’t have time to wait for next day, you need to discharge those capacitors by attaching an appropriate load resistor to it for slow discharge. Do not attempt to discharge them by shorting the terminals, the sound of discharge can be quite high to make you deaf for some time.
When you have the lights fully discharged, first you need to inspect for any burnt components. Usually you may find some small capacitors on the PCB either leaked or swollen. Replace all the bad capacitors with appropriate value. Sometimes these capacitors look find from top but when you take them out of the PCB, you will see that they have leaked. Pronlinchrom 23 that we were repairing had same issue, the small capacitors on the PCB looks fine from top and even show some reading on multimeter but when taken out, they were leaked and obviously were working on very much reduced capacity. Next thing to check is the relay. Use a 12v power supply and connect it to the input of relay.
You should hear a click sound on connecting the power to relay. Once the relay is checked, move on to the big load resistor which you see with the heat sink. This big resistor going bad is the most common fault in these lights. Set your multimeter to lowest Ohm reading and connect the probes to each side of the resistor. Multimeter should display the reading exact or very close to what is printed on the resistor heat sink. Ours had 33E printed and the multimeter displayed 33 Ohms which means resistor is fine. If the resistor is bad then your multimeter will not show any reading or show a very high reading. Once you figure out that this resistor is bad, you need to take it out from the light and replace it with a new one. If resistor is mounted on a heat sink, you also need to apply a fresh coat of thermal paste on new resistor before mounting it on heat sink.
Once you have resistor changed, always double check for relay because this main resistor can go bad if relay does not work on time after the flash. Also there is a Triac present on circuit board which drives this relay, check the health of this triac as well using multimeter. Usually the triac does not go bad if it’s of good quality and operating within its specified voltage rating.
Once you have checked relay, caps, main load resistor and the triac and you cannot find any other sign of damage then you can test your light. But do not plug the lights straight away for this time. Take a 40W incandescent bulb and attach it in series with any one of the wire in power line.
Now switch on the power and you should see the bulb light up for a second and then goes dim. This indicates that there is no short circuit in the system. Now fire the flash and try to listen for relay clicking. Also check temperature of main load resistor heat sink. If you hear relay working and resistor is cold and your light works then it’s all good to go. Notice that flash will not fire on full intensity right now, it’s fine because we have a 40w bulb which is also drawing some power. Now take out this bulb and connect the lights normally to its power cord and it should work on full intensity now.
If your lights are working but intensity of flash has gone down then most probably its time to change its capacitors. When you open the light, you will find two very big high voltage capacitors. These are the ones responsible for holding charge and fire up the flash. Changing the faulty one will restore the low flash intensity issue.
Special thanks to PhotoCraft for providing their lights for this review.