Whelen Dash Miser DOA

One of my Whelen DashMiser II (dual strobe) is DOA. I know the Caps go down when not cycled frequently.

I know how to run a digital meter. Is there a troubleshooting flow scheme that I can look at?

Anyone have a power supply that their willing to part ways with if I can't figure out the issue?

Thanks

Joe

 

[Pete L.]

I seem to remember someone here on the forum say that when a strobe item has been sitting for a long while, you should power it up with the tubes disconnected. It would allow the capacitors to
charge up. Then power off, reconnect the tubes and power it back up.
Worth a try ?

 

[RS485]

@Pete L. -- generally, I'd agree with you - really old caps may need "re-forming" where you need to coax the caps to reform an oxide layer IIRC.
I've done this a few times but only needed to do it for some really old power supplies (late '60s or early '70s.)

So I'd bet we're looking at a component failure in this case.

I'd need to see a couple of good clear hi-res pics of the top and bottom side of your unit's circuit board before suggesting test-points to measure.

Also...alot of Whelen PSs used "hybrid" boards at this point in time. I.e. something like this:

(photo courtesy @JohnMarcson via:

)
If your problem ultimately traces back to one of these...you'll be better off looking for a replacement.

Very generally, we're looking for three possible failures:
1 - inverter (the heart of the power supply) is not generating a high voltage on the primary capacitors connected to the flashtubes
2 - trigger - the trigger circuitry is not delivering a low-amp - very high voltage to the flash tube(s) to cause flash
3 - timing circuitry - the timing circuit isn't functioning so as to ask for the trigger of a flash.

With the above in mind, if you can post the pics I mentioned, I might be able to suggest some points to measure.

 

[JohnMarcson]

Theses are from a time period when strobe supplies became less servicable. As RS485 stated, many of the components are in the potted hybrid board which isn't servicable. Full on DOA is usually a few other things as mentioned above vs. caps aging.

The thing I woukd check on these is the the cigar plug and the board fuses; that's an easy fix. The plug fuse is in the tip of the plug. The board fuses are usually axial and soldered in or sometimes inline with the wires. I don't remember off hand which is more likely. If it isn't a fuse you are better off scavenging a new supply.

 

[Abacus]

Yikes. I will fire up my DM2 this weekend. For those in service who used them frequently on patrol did you ever find there was a time limit when they started to get too hot and stopped working. Or did they just Whelen work.?

 

[QUICKONE]

@Pete L. -- generally, I'd agree with you - really old caps may need "re-forming" where you need to coax the caps to reform an oxide layer IIRC.
I've done this a few times but only needed to do it for some really old power supplies (late '60s or early '70s.)

So I'd bet we're looking at a component failure in this case.

I'd need to see a couple of good clear hi-res pics of the top and bottom side of your unit's circuit board before suggesting test-points to measure.

Also...alot of Whelen PSs used "hybrid" boards at this point in time. I.e. something like this:
View attachment 257354
(photo courtesy @JohnMarcson via:

)
If your problem ultimately traces back to one of these...you'll be better off looking for a replacement.

Very generally, we're looking for three possible failures:
1 - inverter (the heart of the power supply) is not generating a high voltage on the primary capacitors connected to the flashtubes
2 - trigger - the trigger circuitry is not delivering a low-amp - very high voltage to the flash tube(s) to cause flash
3 - timing circuitry - the timing circuit isn't functioning so as to ask for the trigger of a flash.

With the above in mind, if you can post the pics I mentioned, I might be able to suggest some points to measure.

Here's the front and rear views of the P/S. The 12V Cig plug fuse meters out Ok.

I'll re-verify 12V Cig Plug polarity, as someone has replaced the OEM plug.

I tried applying power to the P/S with the Flash Tubes disconnected and; No Change/No Flash.

Please refresh my memory;

What should the 12v Transformer meter out to? It should have two leads on the PRI and two leads on the SEC correct?

What should the CAPS meter out to?

Thanks

 

[QUICKONE]

Theses are from a time period when strobe supplies became less servicable. As RS485 stated, many of the components are in the potted hybrid board which isn't servicable. Full on DOA is usually a few other things as mentioned above vs. caps aging.

The thing I woukd check on these is the the cigar plug and the board fuses; that's an easy fix. The plug fuse is in the tip of the plug. The board fuses are usually axial and soldered in or sometimes inline with the wires. I don't remember off hand which is more likely. If it isn't a fuse you are better off scavenging a new supply.

Are the CB fuses those two silver rectangular boxes, located near the lower right corner of the PS board picture? (but look more like circuit breakers)?

Thanks John

 

[RS485]

Thanks for the pics.
I have a working DM1 with the same board minus the build-out for the 2nd port.


Here some basic measurements I took:
2-5 VDC between "G" and "GND" <----- when running (.350 or so if tube disconnected)

420 VDC between "GND" and "ANODE" (main cap flash voltage)

+12VDC between all red "+"s and "GND" (primary coil voltage)

+8VDC between "8" and "GND" (hybrid board operating voltage)

~0 OHMS between "S" and "GND" (between MOSGET's "source" pin and ground)

Note: the device detects when the tube isn't firing and thus turns the inverter off. This explains the ".350" I mentioned above.

Interesting note: This has a small voltage regulator to power the hybrid board (requiring 8VDC). I've seen these go bad. If we're lucky, maybe that's it!

HTH

Edits/notes: the two rectangular boxes are foil capacitors for triggering the flashtube's trigger transformer (built into the lamp assembly).

The internal fuse is the little green device next to the big fat diode here:
(Please measure resistance across the little fuse, it should be 0 if it isn't blown)

PARTS:
MAIN MOSFET: IRFP140
VOLTAGE REGULATOR: 78L08AC
LITTLEFUSE: (not sure - available at digikey though)

You asked earlier: "What should the 12v Transformer meter out to? It should have two leads on the PRI and two leads on the SEC correct?" - Yes, well, sort-of. The transformer isn't a typical AC transformer. It is a transformer designed to suit a "flyback converter":

Flyback converter - Wikipedia

en.wikipedia.org

I think this patent:

https://patentimages.storage.googleapis.com/fe/72/1b/590040789fc131/US5013973.pdf

best describes this power supply's design (and most xenon strobe Whelen PSs since then).