Hello syed

Blinking output means, in the most of the failure cases of such power supplies, that a protection circuit is getting energized for some reason (that you are called first to identify and then delete).
This practically means that the protection circuit “sees” either a tendency for overvoltage at the output or perhaps some kind of overloading as the output voltage tries to build up.
You can start the easy way, by a visual check of the output electrolytic capacitors.
In order for me to enter in further technical troubleshooting details, I would like you first of all to describe to me your technical profile. The reason is simple. I would never try to expose you (or anyone else, no matter if he or she likes electronics) to the risk of possible electrocution of any degree. Needless to refer to the worst case scenario...
So, evaluate please your skills and let me know in turn if you really are capable to “swim in deep waters”.
If you already feel that this task is beyond your skills, suitable for a properly qualified technician, I would kindly suggest you to quit from the idea of any further intervention no matter how tempted you may be for repairing the unit by your self.
Always remember that you alone are the undertaker of the full risk against your own life and also responsible for the application of your personal skills for implementing any advice that you may receive from anyone interested to help you. This should be fully understood in advance.

Best Regards

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Hi Paris,

Thanks. I meant that in the next few years as the thermal grease ages I might start having issues. I'm not sure how long the grease is good for. And building & installing the wires would not take me long to do. I appreciate your help.

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Hi Robert

Before doing this, just check out its necessity.
So, verify first the current share between the transistors. If this verification shows you equal current flow between every transistors' C-E, you don’t have to do anything more for improvement.
The method is straightforward. Put a reasonable load at the output, say 1A. The voltage is not important for this check. So you can connect a 12V/10W lamp at the output, one of those used for car turn signal light indication, and measure afterwards the voltage drop across every current sharing resistor.
Under normal conditions you should read almost the same mV value across each resistor, that is, equal current flow in every transistor.
To make things even more easier, when taking the first voltage depress the REL button of your Fluke. From now on, this value will be stored in its memory as a reference. This will then be compared with the rest of them each time you take a new measurement and give you the difference from the stored reference.
Now you already have the overall picture of the total current as it is divided in three equal sub-currents within the transistors, which add again at their common emitter connection point.
In conclusion, if you notice small differences, say around 5-10mV, you don’t need to make any further improvement.
On the contrary, if you notice great declinations between the measurements (which are not expected because all of the transistors share a common heatsink), only then you should bridge the collectors together with copper wire of proper diameter (and this finally will signal that something is wrong with the compound used)…
So, apply Ohm’s law, use reasonable percentage tolerance for the differences (if any) and common sense to decide for a more drastic intervention.
These guidelines will help you save valuable time, otherwise spent in vain…

Best Regards

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Hi Paris,
I'm going to run wires to the other transistors to make sure that I don't have problems with them in the future. No sense in taking unnecessary chances. Thanks.

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Hi Syed,

The SMPS is trying to work. I would trace the blinking circuit back from the output and find the culprit. I hope you are not working on it without an Isolation Transformer.

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You are very welcome. You will be very happy with the visor. It also uses 3 AAA batteries and better LEDS than the cheap ones.

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Hi Randy,

Transistors that do not conduct the collector through the heatsink will not have the collector pin cut and will have a thermal conducting plastic looking piece between the transistor and the heatsink, or will not have an exposed thermal plate on it's back that could make contact.

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thanks, Robert, much appreciated!

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