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Repairing a Hoskin Strobe power supply (P/N 701295 3A14VDC)


NicoN

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A few weeks ago, our LH strobe light  quit the service.

After a few hours of trying with other strobelights, I decided that the power supply is the reason for the failure. I also found out, that there is a third power supply for the tail!

Nobody has ever seen the tail flashing – only the normal NAV-Light.

 

Here is my story of bringing 2 power supplies back to work.

The first one obviously had visible damage to the big capacitors on top of the circuit. Blown out gaskets and the electrolyte spread over the PCB casuing some corrosion.

As a first job, I exchanged  those 2 Caps with stronger ones (220µF/600V).

The power supply started flashing again, but with pretty low power consumption (~40mA) instead of something near 3Amps and only 1 flash every 70s.

The other compoments looked fine and undamaged. Nevertheless, I decided to change the two 100µF Caps with 100µF/63V parts. Better. 1 Flash every 18s, still low power consumption.

The adjustable resistor did not change this behavior.

In a nutshell, after hours of re-engineering the schematic and trying to test  the transistors in the circuit, I decided to change the 3 transistors also.

Perfect, now. Flashing with about 0,5Hz, you can adjust the power consumption with the potentiometer to the desired ~3A. But it does not really change the frequency. It may change the flash intensity but not much.

And it does not smoke!

The second power supply was different! No visible damage to any parts.

Symptoms: 2A power consumption for the first 1-2seconds, decreasing to 100mA with the typical sweeping sound of a loading flashlight. 500V! on the connector to the strobelight, but no flash!

I did the brute force approach now to save time. I changed all transistors and all caps.

Works! Time needed about 1,5hours.

Here are some more tips to accelerate the job:

  • -          You are working with high voltages of about 400-500V. Always unload the capacitors before doing anything. This includes longer times of waiting!

  • -          First check the small fuse soldered onto the PCB directly next to the red wire. It may be burned.

  • -          Don’t think too much. Change all the typical failing components together and do not try to change them in by one. Saves you time. The parts cost about 15-20€.

  • -          It is more difficult to get the parts. I ordered the parts from different sources, but it tunred out that digikey or Mouser should have all the  parts.

  • -          Make sure the parts you order are from the right size and not too big dimensions. One problem for me was, that an important orange cap was bigger than the original.

  • -          Always make sure you have the right polarity for any part!

  • -          Make sure to solder the new parts pretty close to the PCB. Otherwise you may run into problems when re-assembling the power supply. Especially the 2N2907A and the cap next to it can collide with the connector for the strobe-light.

This ist he part-list from digikey:

Index    Menge Teilenummer    Hersteller-Teilenummer              Beschreibung    Kundenreferenz                Lieferrückstände             Stückpreis          Gesamtpreis

3             3             MJE182STU-ND                MJE182STU        TRANS NPN 80V 3A TO-126                        0             0,43000 1,29 €

4             3             2N2907ACS-ND 2N2907A             TRANS PNP 60V 0.6A TO-18                       0             2,05000 6,15 €

5             3             TIP35CGOS-ND TIP35CG              TRANS NPN 100V 25A TO247                     0             2,25000 6,75 €

6             3             338-4220-ND     715P22456MD3 CAP FILM 0.22UF 5% 600VDC RADIAL                    0             5,12000 15,36 €

 

Additionally, you need:

2             Caps 220µF 400 or 600V

2             Caps 100µF 63V

Good luck!

Other power supplies from other manufacturers should work in a similar way.

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Yes, that is the right way. But when thinking of about 1300€ for Whelen Orions left/right & tail it is worth the work!.

 

But I still have some minor issue with the strobes. See my other post .

 

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  • 2 years later...

Here's a hand sketched reverse engineered schematic in case of use to anyone else repairing these themselves. I've had to replace the two big capacitors twice on one unit, since I neglected to reform the identical (Sprague 39D series) "new old stock" replacement units I bought from Mouser. The first (not reformed) set shorted out after a few months in service. The second set I reformed overnight on a high voltage power supply before installing them, so hopefully they'll last longer. The original soldered leaded small glass fuses are Bussmann GFA-4 and quite expensive.

Hoshkins_701295_strobe_power_supply.jpeg

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Great work!

I tried myself to do it using a schematic software.

I spent many hours and finally gave up because of the same loops I can see in your layout :-)

I chose the brute force method and changed all capacitirs

 

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  • 2 months later...

Thanks, btw I forgot to include the Littelfuse CG230 gas discharge tube that goes from the 0.22uF capacitor ("sync" input) to ground. This device will trigger (short to ground) once the lower 200uF capacitor has reached 230VDC and dump the charge from the 0.22uF capacitor into the step-up transformer (located in the strobe light assembly) to trigger a flash.

The yellow sync leads from all three power supplies (wingtips and tail) are connected together so that whichever supply's CG230 first reaches 230VDC will trigger a flash on all three synchronously.

If the yellow sync lead is simply left open (e.g. power supply bench test), this small gas discharge tube is what will trigger a flash.

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  • 2 months later...

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