need schematic for whelen aircraft strobes

[dacflyer]

anyone have access to whelen aircraft strobe schematics ?

the model i have is A413A HDA DF 14/28
FAA PMA/STC SA615EA & SA800EA

DATE SEPT 90
SER 36853

this unit is having a really weird problem, origionally it had a blown fuze and the power transistor was shorted,
i replaced the transistor, and the fuze, it fires fine for a while,,then it spazzes out,,,the transformer squeels like a stuck pig,,and the tube sustains an arc..almost giving a symptom of bad caps,, i substituted them, and it still does it, if i let it on too long then the transistor blows again. its almost sounding like what ever is driving the transistor is screwing up.. i am having a hard time trying to diagnose this, with power on,, otherwise the magic smoke wants to come out.
so this is why i need the schematic,,
i have much experience working strobes,,but this one has me baffeled.
i know someone here works on aircraft electronics,, i just cannot remember who..
please help if you can.. thanks

[jwax]

You probably checked here already, but just in case:
http://www.whelen.com/pb/Aviation/Anti- ... Manual.pdf

Sounds very specialized- Do you have an aircraft repair, or is this strobe for the "flyer" part of dacflyer? (Your glider)

[jollyrgr]

I doubt you will find a schematic for that device as this is not considered a "field serviceable" device. Most things in aviation MUST be repaired by certified and licensed technicians. I KNOW you are likely using this on an ultralight or experimental aircraft that will give you some ability to service it yourself. But my guess is having the schematic available will be next to impossible.

That being said I can relate what I know about strobes in general. As you know (you state you are familiar with strobes) in DC powered devices there is a switching transistor that is part of a transformer circuit used to step up the 12V to 24V (or whatever) to 200V to 500V. This is the "power" to the flash tube. There is also a trigger circuit that produces an impulse in the 4000V or much higher range. In a number of strobe circuits I've found the high voltage capacitor shorts out after time. Probably that is not the "true" problem (maybe it dries out????). Remove the strobe tube or at least disconnect one of the power wires and the TRIGGER wire. On the aircraft version this is usually simple enough to do by unplugging the tube.

In any case if you lift one end of the "big" storage high voltage cap the oscillator should run and in many cases will be at the high end of human hearing. In other words you can hear it oscillate, depending on how good your hearing is. You can throw a neon test lamp across the output with the capacitor removed (one of those 90V to 500V test lamps used for testing line voltages) to see it flicker.

Possibly connect a known good cap across it and measure the DC voltage. Again, no tube should be connected. If the oscillator works fine on a known good cap, try connecting the original back in place. If you get weird results, suspect the main storage capacitor. There is another thing I have found that goes wrong.

Based on your description of "then it spazzes out" it sounds (no pun intended) as if the trigger device is breaking down too soon. Different devices such as neon tubes and diacs are used to give the impulse drive to the trigger transformer. If this is happening it will cause the main charging transformer and capacitor to never reach a full charge and be overloaded.

[dacflyer]

the triggering section is fine,,its the oscilator thats not working right for charging the cap,,,the main storge caps are fine, and i even substituted dummy loads etc.. i just cannot fire it up long enough without taking out the drive transistor,
the circuit is weird to me because, if i take the base loose,,theres no drive signals to measure,, just voltage..i only get a drive signal whent he base is connected, Hmmm

its not like a tv set where i can measure the base of the signal for the HORIZ drive.. if you know what i mean...

[Edd]

.

Sounds like quite a bit more of specifics are required....so I'll just initially do an inter fill and hit upon some touch points:

This unit is having a really weird problem, originally it had a blown fuse and the power transistor was shorted,
I replaced the transistor, and the fuze,

That description, making it sound like the basic power supply circuitry is merely one transistor working as a reflex osc feeding a power xformer and secondary Pwr Supply rectification and charging up the units flash cap bank and then they are then sitting there connected across the strobe flash tube and waiting for the unit to be repetively triggered…and then to recycle after flashing …right ?

it fires fine for a while, then it spazzes out,,, and the tube sustains an arc.

Meaning that the strobe works totally normal on its initial few /several light discharges in both flash level intensity and timing…. right?

the transformer squeals like a stuck pig,

Being free running, typically the noise from the up converter transformer will be at a lower frequency at the caps initial discharged state and then gradually rise in frequency as the initial drain of storage capacitor charging tapers off. If the recharging is making a lower frequency “squealâ€

[dacflyer]

ok EDD i have to look at it later on today when i get back home from work..
but the tubes are fine. i am using 4 tubes, on this unit..i have isolated the tubes etc. they are not the problem,,its something in the charging circuit
when it does this one or 2 tubes will stay lit, not full intensity, but as if its just an arc in it.. you can do this with any strobe if you disconnect the caps. but as i said before also the caps are fine,
i am wondering if the transformer is having HV break down,
the transistor crossed to a NTE2375 , i do not have the origional # in my mind right now, but its a FET
sometimes also the unit acts up right away too, more so lately
i trry to check it out, but then gets aggeravated and quit for a day or so.
anyway i'll give more info tonight when i get home.

[Dave Dixon]

>i know someone here works on aircraft electronics,, i just cannot remember who..

Thinking of me?? Yup, I work on aircraft instruments, but we don't do strobes. I DO have an old supply/lamp in my junk box somewhere at home that works, but have no idea of the MFG. I'll see if I can find it, and what info might be attached to it. Best of luck,
Dave

[dacflyer]

hi dave,, ya its you,,lol couldn't remember your name O_o

its bad to have a fotographic memory......its gone in a flash..lol

anyway..i'd be thrilled if you might have access to any info,,thanks..
all info is at the top of here..

[jwax]

Just a quick thought dacflyer- Do you have any freeze-spray? Maybe chill the FET or transformer to localize a fix?

[dacflyer]

tried that already, actually its not the heat thats killing the fet,, its the unstable oscillation, i tried it on other components also. no effect.

[dacflyer]

update,,, did some more test,, the strobe is basically doing this..

it charges up... fires the strobe tube once then sustains the arc..

why isn't the arc extinguishing ?

i belive this is why its killing the power supply power transistor...

i am using a 60 watt test tube on this unit..as i have used it on many other strobes in the past.. this is just blowing my mind..

[Chris Smith]

Your problem is in the gate section.

Much like a transistor gate, the middle of the tube needs a jolt. [voltage]

Usually around 400 volts, sends the tube into conduction of 4kv. [Flash]

Yours seems to keeps the gate open and supplying some form of current to cause a discharge, most likely the SCR that feeds it?

With the feed voltage trying to build up, and the "Gate" keeps trying to fire at will, It never achieves real firing capacity.

I don’t have your diagram, but I have fixed and sold a few strobes.

[dacflyer]

i removed the SCR's and manually triggered it, it still does the same thing
i just touch the contacts to make it flash and it still does the same thing,
so i know the triggering circuit is not the fault..
if i continue to let it sustainthe arc for more then a second or so, the driver transistor releases the magic smoke,

[jwax]

Once again dacflyer (also obvious)- Do you have another unit available to swap parts with, or is this a one-of-a-kind unit?
Would a call to tech service at Whelen help?

[dacflyer]

no i do not have another unit to swap parts with,,but i have already substituted most of the important parts...caps , SCR's flash tubes.
i get all the same results,,and whelen will not help anyone thats not FAA
certified....