Old Whelen Power Supplies

RS485

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So technically, this _is_ an old Whelen power supply! Just not for a strobe :)
Whelen had a portable scene-light product called the "NITEBEAM" -- at this point, the only evidence I can find of this product on the interwebs is the install manual (attached) copyrighted 1998.

I got a hold of an original Whelen power-supply (part listed on eBay) and hooked it up to a 70-watt metal-halide bulb and it works as expected.

This power supply has to:
1. Supply a relatively high voltage, low-current output to the bulb to initiate the arc (just like a conventional Xenon flash tube)
2. Once the arc is established, resistance is low. The PS must now kill the high-voltage output and feed a relatively low-voltage, current-limited output to sustain the arc, let the tube warm up, then:
3. Maintain the current limit and keep the lamp running.

Because the PS is potted, I 'm unable to examine the circuitry but I have I suspect what Whelen learned and applied to their strobe PSs (w/r/t sensing flashtube firing, and sensing current through the primary coil of the inverter), was applied to this PS with a different purpose in mind.

I gather the product itself didn't sell terribly well...but I think it was cool and interesting none the less.

Here's a vid of it starting up, running, and being turned off:

https://youtu.be/SX-3cHEIyTA
 

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ur20v

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So technically, this _is_ an old Whelen power supply! Just not for a strobe :)
Whelen had a portable scene-light product called the "NITEBEAM" -- at this point, the only evidence I can find of this product on the interwebs is the install manual (attached) copyrighted 1998.

I got a hold of an original Whelen power-supply (part listed on eBay) and hooked it up to a 70-watt metal-halide bulb and it works as expected.

This power supply has to:
1. Supply a relatively high voltage, low-current output to the bulb to initiate the arc (just like a conventional Xenon flash tube)
2. Once the arc is established, resistance is low. The PS must now kill the high-voltage output and feed a relatively low-voltage, current-limited output to sustain the arc, let the tube warm up, then:
3. Maintain the current limit and keep the lamp running.

Because the PS is potted, I 'm unable to examine the circuitry but I have I suspect what Whelen learned and applied to their strobe PSs (w/r/t sensing flashtube firing, and sensing current through the primary coil of the inverter), was applied to this PS with a different purpose in mind.

I gather the product itself didn't sell terribly well...but I think it was cool and interesting none the less.

Here's a vid of it starting up, running, and being turned off:

https://youtu.be/SX-3cHEIyTA
So it's an HID ballast... Does it have a separate igniter on the bulb, or is it built into the ballast? Does the lamp have a number on it? A lot of the early HID stuff was DC/DC, and it took a while for lamp sizes to standardize. Unfortunately much of the early HID stuff was a flop and is impossible to replace today - just ask Lincoln Mark VIII LSC owners. Their only options are to buy extremely rare/expensive used parts (risky) or adapt cheap Chinese bullshit HID kits to their headlights (stupid). Well, there was a third option, but most of those LSC owners were too proud to "downgrade" to factory halogen lights.
 
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RS485

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So it's an HID ballast... Does it have a separate igniter on the bulb, or is it built into the ballast? Does the lamp have a number on it? A lot of the early HID stuff was DC/DC, and it took a while for lamp sizes to standardize. Unfortunately much of the early HID stuff was a flop and is impossible to replace today - just ask Lincoln Mark VIII LSC owners. Their only options are to buy extremely rare/expensive used parts (risky) or adapt cheap Chinese bullshit HID kits to their headlights (stupid). Well, there was a third option, but most of those LSC owners were too proud to "downgrade" to factory halogen lights.
The igniter is built into the ballast. I'm using a pretty common commercial 70W metal halide bulb - a Philips MHC70/U/M/3K (3K for color temp, rather "warm" - they also make a 4K) - ANSI designation is "M98/M143/E"

In the case of the NITEBEAM, I *think* Whelen borrowed more from the commercial lighting market than the automotive. If I ever get my hands on a full unit (or even just Whelen's bulb, part #34-1816623-4E), it should be obvious.

BTW: Did you ever get your DashMaster-II working?
 
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JohnMarcson

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Now there's a niche of a niche... you own any of those, @JohnMarcson
I do not... yet. I'm trying to place that particular white ballast. I've seen it before....

Ahha! I have, it was borrowed from their aircraft line.... like many great Whelen ideas.
The current versions look a bit different, but the 1998 versions were definitely shared between aviation and these beacon and advantedge designs.

I could pony up the $300 per bulb and $550 per ballast and bake a beacon I suppose, but i will just wait until one randomly shows up for sale I think.
 

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PXL_20220911_133851514.MP.jpg

I know this is for aircraft supplies obviously, but what does it do and how? Does it synch two supplies? It has a red, black and orange wire.
 

RS485

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View attachment 238998

I know this is for aircraft supplies obviously, but what does it do and how? Does it synch two supplies? It has a red, black and orange wire.
I've never tinkered with with one of these - my *guess* (given it says, "MAX LOAD 10 AMPS") is that it feeds current to PSs of the era and just cuts that power off a tad early which would have the effect of causing them to flash. More to come... (just ordered one to tinker with :) )
 
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RS485

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I've never tinkered with with one of these - my *guess* (given it says, "MAX LOAD 10 AMPS") is that it feeds current to PSs of the era and just cuts that power off a tad early which would have the effect of causing them to flash. More to come... (just ordered one to tinker with :) )


I received one of these synchronizers.
Attached is detailed pic including a rough schematic and where its laid out on the board.
I had to replace the timer IC as well as the 2N4442 SCR before I got any kind of expected behavior.

I tried testing on a couple of "A490" single-head aircraft PSs, plus a couple of older model "HS" units.

Best I can say is it "sort-of" worked with the A490s but had problems with the HS units. With A490s, the timing seemed slower than the intended 40-50 FPM.
With the HS units, they just seemed to flash on thier own a couple times, then stopped working altogether.

I *think* there is a kind of current-sensing going on where the synchronizer reacts to current drawn on its output pin (orange wire) and for reasons I don't yet understand, the "HS" power supplies seems to get it into a tripped up state where it won't feed enough current to charge the PSs...but it's drawing enough so it stays in the stuck state. Once power pulled from, then reapplied to the synchronizer, it recovers for a few flashes then gets stuck again.

That said, I have only one of these units - it was made in '79 then repaired in '83. I have nothing else to compare it to so maybe something is still wrong.

Taking a step back and comparing the design strategy to that of the A490A, I think the A490A's sync is superior. It is an explicit 3rd wire going right into the timing/trigger circut. Its more robust in that if the master unit fails to deliver the expected sync signal, the subordinate will just flash on its own. A similar strategy is used in the monster System14 ambulance power supply system.

In contrast, the "A490 TP" seems to approach synchronization _indirectly_ by manipulating power and that seems like a bit of a hack.

Still, its an interesting little device to tinker with :)
 

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JohnMarcson

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I received one of these synchronizers.
Attached is detailed pic including a rough schematic and where its laid out on the board.
I had to replace the timer IC as well as the 2N4442 SCR before I got any kind of expected behavior.

I tried testing on a couple of "A490" single-head aircraft PSs, plus a couple of older model "HS" units.

Best I can say is it "sort-of" worked with the A490s but had problems with the HS units. With A490s, the timing seemed slower than the intended 40-50 FPM.
With the HS units, they just seemed to flash on thier own a couple times, then stopped working altogether.

I *think* there is a kind of current-sensing going on where the synchronizer reacts to current drawn on its output pin (orange wire) and for reasons I don't yet understand, the "HS" power supplies seems to get it into a tripped up state where it won't feed enough current to charge the PSs...but it's drawing enough so it stays in the stuck state. Once power pulled from, then reapplied to the synchronizer, it recovers for a few flashes then gets stuck again.

That said, I have only one of these units - it was made in '79 then repaired in '83. I have nothing else to compare it to so maybe something is still wrong.

Taking a step back and comparing the design strategy to that of the A490A, I think the A490A's sync is superior. It is an explicit 3rd wire going right into the timing/trigger circut. Its more robust in that if the master unit fails to deliver the expected sync signal, the subordinate will just flash on its own. A similar strategy is used in the monster System14 ambulance power supply system.

In contrast, the "A490 TP" seems to approach synchronization _indirectly_ by manipulating power and that seems like a bit of a hack.

Still, its an interesting little device to tinker with :)
Interesting. I love the actual insight into the workings that I otherwise don't see. I think my synchronizer is NOS if you need to compare or test further I can send it over. It is ironically sitting on top of my ambulance system with the synchronizer.
 
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RS485

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Interesting. I love the actual insight into the workings that I otherwise don't see. I think my synchronizer is NOS if you need to compare or test further I can send it over. It is ironically sitting on top of my ambulance system with the synchronizer.
John, thanks! for the kind offer but I think its best to keep your device in pristine condition. It would be great if we could find _some_ kind of literature on the device but given their age/era, its a paper needle in a haystack.
 

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John, thanks! for the kind offer but I think its best to keep your device in pristine condition. It would be great if we could find _some_ kind of literature on the device but given their age/era, its a paper needle in a haystack.
I have been occasionally searching for at least a catalog sheet, preferably a patent or data sheet, on these with no luck. If anyone finds anything I'd love to see it. Let me know if mine is needed for "science".
 

RS485

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I don't think that's the synchronizer -- If you compare that patent to the guts of your earliest commander beacon (with the "AEI/L" board), I think you'll see it describes it pretty well.
Where you see "LOAD" in that diagram, that represents the flashtube and (back then) the external trigger circuitry. "C3" and "C4" are the signature large capacitors. The "T1" transformer is the big transformer with ~8 wires coming out of it and "Q2" is the main NPN power transistor.
 

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I don't think that's the synchronizer -- If you compare that patent to the guts of your earliest commander beacon (with the "AEI/L" board), I think you'll see it describes it pretty well.
Where you see "LOAD" in that diagram, that represents the flashtube and (back then) the external trigger circuitry. "C3" and "C4" are the signature large capacitors. The "T1" transformer is the big transformer with ~8 wires coming out of it and "Q2" is the main NPN power transistor.

What's odd is the patent numbers match exactly, but even the description seems more like it is describing a portion of the actual supply. I will dig a bit deeper.
 

RS485

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Attached is a pic of model "A413 HD-14" mfg in '78. It has the same patent sticker.
Yet, US4013921 filed in '75, granted in '77 more accurately describes that PS's inverter guts. In particular, R5,R6,R7 and Q3, Q4, and Q5, comprise part of the circuit described as,

"Thus, in the customary manner of operation of a Schmitt trigger circuit, transistor O3 will be locked in the conductive condition when its base voltage exceeds a reference established
by the setting of variable resistance R6 and by Zener diode ZD1"

This part of the circuit is meant to turn off the inverter when the cap charge level is reached (i.e. when there's a risk of overcharge as when the flashtube is failing).

In US3515973 (the sticker) that same functional aspect is described as,
"Thus, when energy storage capacitors C3 and C4 are
charged to NXE volts diode D5 will conduct during the
"off" (energy transfer) time of power transistor Q2 there
by preventing further transfer of energy to storage capacitors
C3 and C4. When diode D5 conducts, the energy
stored in the primary winding of transformer T1 during
the “on” time of power transistor Q2 is "pumped back'
to the source."

Of the PSs I have, those that arrived with exploded caps most often embodied US3515973 so I gather this design feature may not have been terribly robust.

But the takeaway for us might be that the sticker added on to a PS or SYNC may not necessarily apply well to the device it's been slapped on.


On the right side of the pic, is an attempt to mock up just the power control part if the SYNC (i.e. the 2N4442 SCR and TIP34B PNP power transistor) to try to get to know these parts a little bit better :)

Personally, this is why I dig US4321507 -- it seemed to consolidate the best ideas Whelen (Austin) had from the past and tossed in a few good ideas for the future to carry Whelen to US5013973 which introduced MOSFET-based inverter and Comet flash.
 

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RS485

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Regarding the aircraft SYNC:

Bottom line: I believe the SYNC was only intended for specific aircraft power supplies designed for it.

Those model numbers I know of are:
A490-HT,1
A490-T,1

There may be other models but I haven't seen them.

Details indicating an intended SYNC power supply are:
1 - Visible fuse on the back of the aluminum case.
2 - Elements of the circuit connected to the high side _in front of_ the inductor/coil.

The fuse protects the SYNC in the event that the power supply shorts out (otherwise the short would damage the SYNC)

Synchronized triggering is achieved within the power supply by sensing a slight variation in line voltage produced by the SYNC device. Power supply's coil acts to dampen sudden voltage changes so this sensing circuitry is uniquely placed _before_ the coil and is a tell-tale sign its designed for SYNC.

I also came a across a couple of "A490-HT" units both made in early '73. They aren't syncable but their timing/trigger circuit consists of a single spark-gap and when working, you can see a tiny spark within. I've never seen it before in any other PS.

The SYNC module has a large coil/inductor to shield stray voltage changes from causing false triggering and implements its voltage varying _after_ its own coil.

Of the five working syncable PSs I have, the earliest (A490-HT,1) were all made ~1973. The A490-T,1 models were made in '74 and '79
 
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JohnMarcson

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Regarding the aircraft SYNC:

Bottom line: I believe the SYNC was only intended for specific aircraft power supplies designed for it.

Those model numbers I know of are:
A490-HT,1
A490-T,1

There may be other models but I haven't seen them.

Details indicating an intended SYNC power supply are:
1 - Visible fuse on the back of the aluminum case.
2 - Elements of the circuit connected to the high side _in front of_ the inductor/coil.

The fuse protects the SYNC in the event that the power supply shorts out (otherwise the short would damage the SYNC)

Synchronized triggering is achieved within the power supply by sensing a slight variation in line voltage produced by the SYNC device. Power supply's coil acts to dampen sudden voltage changes so this sensing circuitry is uniquely placed _before_ the coil and is a tell-tale sign its designed for SYNC.

I also came a across a couple of "A490-HT" units both made in early '73. They aren't syncable but their timing/trigger circuit consists of a single spark-gap and when working, you can see a tiny spark within. I've never seen it before in any other PS.

The SYNC module has a large coil/inductor to shield stray voltage changes from causing false triggering and implements its voltage varying _after_ its own coil.

Of the five working syncable PSs I have, the earliest (A490-HT,1) were all made ~1973. The A490-T,1 models were made in '74 and '79
We learn more about these early aviation supplies every time you post. This subject is very interesting especially because of the crossover into the vehicle products. I never get tired of learning more about this subject, thanks for keeping the discoveries coming.
 

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Here is one that i just took off of a 5000 beacon, looks a little different than the previous one. It doesn't work, no green cardboard tag and no signs of life at all.

PXL_20221026_015453539.MP.jpgPXL_20221026_015458406.MP.jpgPXL_20221026_015503003.MP.jpgPXL_20221026_015507536.MP.jpgPXL_20221026_015517066.MP.jpgPXL_20221026_015529494.MP.jpgPXL_20221026_015536959.MP.jpgPXL_20221026_015557715.MP.jpgPXL_20221026_015607836.MP.jpg
 
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ur20v

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Here is one that i just took off of a 5000 beacon, looks a little different than the previous one. It doesn't work, no green cardboard tag and no signs of life at all.

View attachment 240122View attachment 240123View attachment 240124View attachment 240125View attachment 240126View attachment 240127View attachment 240128View attachment 240129View attachment 240130

The only way to truly test it would be to bridge the capacitor terminals with your tongue...





(If there are any mental midgets out there reading this, DON'T DO THAT! It was a joke, not actual troubleshooting advice.)
 

RS485

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Here is one that i just took off of a 5000 beacon, looks a little different than the previous one. It doesn't work, no green cardboard tag and no signs of life at all.
<snip>
WOW! A four digit board serial number! I'd place this around ~72/73. Pretty neat PS!

Attached is a quote from a Whelen aircraft catalog documenting a change in FAA regs in August of '71 requiring significaly brighter anti-collision lights (from 100 candela to 400).

I'm guessing this was a factor in Whelen(/AEI)'s design of these more powerfull PSs.

------
If its not drawing any current then I'd look for a cold solder joint following in from the supply leads.

The timing/trigger is the daughter board mounted on top. You can see the red-wire feeding it +12V. You should be able to measure +12V there relative to GND.

More trouble shooting:
First, I'd let US4013921 be the guide. It best describes this PS (minus the double-flash stuff)

Testing points can sometimes be tricky due to the conformal coating applied to the PCB. I have to really jab test leads in to get through to make contact with the solder.

Points to test (see attached):
1. This feeds the primary side of the transformer. You should see +12V here. On my unit, there's a white jumper wire between this terminal and the +12V on the front side of the PS - check its integrity.

2. You should see +12V here, too.

3. You should see somewhere around +1.5 to +3V. This provides the critical "starting bias" discussed in the patent.

4. You should see GND here -- there should be ZERO resistance between any of these points and GND

5A/B/C. There should be high resistance between the left-most(5A) and right-most(5C) pins here. This is transistor "Q5" in the patent. It is only supposed to turn on when voltage across the primary caps is sensed to have reached a state of full-charge. You should measure 0V (or less that 0.7) on the center pin(5B) of this transistor. If you measure higher than that, then something is wrong in the sensing circuit and its shorting the "starting bias" to ground and preventing the inverter from starting.

Other ideas: Maybe the primary caps are so shot, they're allowing the sensing circuit to kick-in. I'd expect to hear a very brief high-pitch whine in this case, though.

Maybe both power transistors are shot. Seems unlikely but if they're seeing that "starting bias" and everything else checks out, then they're the only thing left.
 

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JohnMarcson

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WOW! A four digit board serial number! I'd place this around ~72/73. Pretty neat PS!

Attached is a quote from a Whelen aircraft catalog documenting a change in FAA regs in August of '71 requiring significaly brighter anti-collision lights (from 100 candela to 400).

I'm guessing this was a factor in Whelen(/AEI)'s design of these more powerfull PSs.

------
If its not drawing any current then I'd look for a cold solder joint following in from the supply leads.

The timing/trigger is the daughter board mounted on top. You can see the red-wire feeding it +12V. You should be able to measure +12V there relative to GND.

More trouble shooting:
First, I'd let US4013921 be the guide. It best describes this PS (minus the double-flash stuff)

Points to test (see attached):
1. This feeds the primary side of the transformer. You should see +12V here. On my unit, there's a white jumper wire between this terminal and the +12V on the front side of the PS - check its integrity.

2. You should see +12V here, too.

3. You should see somewhere around +1.5 to +3V. This provides the critical "starting bias" discussed in the patent.

4. You should see GND here -- there should be ZERO resistance between any of these points and GND

5A/B/C. There should be ZERO resistance between the left-most(5A) and right-most(5C) pins here. This is transistor "Q5" in the patent. It is only supposed to turn on when voltage across the primary caps is sensed to have reached a state of full-charge. You should measure 0V (or less that 0.7) on the center pin(5B) of this transistor. If you measure higher than that, then something is wrong in the sensing circuit and its shorting the "starting bias" to ground and preventing the inverter from starting.

Other ideas: Maybe the primary caps are so shot, they're allowing the sensing circuit to kick-in. I'd expect to hear a very brief high-pitch whine in this case, though.

Maybe both power transistors are shot. Seems unlikely but if they're seeing that "starting bias" and everything else checks out, then they're the only thing left.

If you don't hear back from me in 24 hours just know that I died trying to fix this power supply..... Thanks for the insight.
 
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JohnMarcson

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PXL_20221026_145855807.MP.jpg

I I'm pretty sure right there at the yellow wire there is an electrical component above it that looks exploded or broken...
 

RS485

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View attachment 240139

I I'm pretty sure right there at the yellow wire there is an electrical component above it that looks exploded or broken...
Nice observation, John!
That would be a "5061" diode as per:
That's "D2" and "D2'" in the patent.
If its shorting, then it would be diverting the starting bias to ground. If you measure very low resistance between those two points...that would prevent it from working!

(NOTE: It's a diode -- it's meant to let current pass in one direction but not the other -- in this case, it's meant to protect the transistor's base from getting hit with a negative spike on the back half of the inverter cycle I.e. just after it shuts off and the coil's magnetic field collapses
Its in parallel with other stuff, mine measures 200 OHMS both ways so you may have to desolder the part and test in isolation. You could try desoldering the yellow wire. It that diode is shorting to ground, then if you cut out that yellow wire, it should allow the other side/transistor to work and should show _some_ signs of life)

On my unit, there's one of those mounted on the _inside_. It's curious how its on the outside here.
 
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Nice observation, John!
That would be a "5061" diode as per:
That's "D2" and "D2'" in the patent.
If its shorting, then it would be diverting the starting bias to ground. If you measure very low resistance between those two points...that would prevent it from working!

(NOTE: It's a diode -- it's meant to let current pass in one direction but not the other -- in this case, it's meant to protect the transistor's base from getting hit with a negative spike on the back half of the inverter cycle I.e. just after it shuts off and the coil's magnetic field collapses
Its in parallel with other stuff, mine measures 200 OHMS both ways so you may have to desolder the part and test in isolation. You could try desoldering the yellow wire. It that diode is shorting to ground, then if you cut out that yellow wire, it should allow the other side/transistor to work and should show _some_ signs of life)

On my unit, there's one of those mounted on the _inside_. It's curious how its on the outside here.
With the yellow wire removed it ramps up but never fires. With the yellow connected but the disintegrated diode gone it ticks in time but doesn't power up
 

RS485

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Could be that power transistor is damaged such that its interfering with the feedback that's supposed to drive the transistors into saturation.

I can't explain how this prevents flash (in the "ramps up" scenario).

When it ramps up...does it stop on its own? We'd expect the cap-voltage sensing circuit to kick in and clamp the inverter off at some point. If that's not happening, could be we're not building enough charge to flash. We'd need at least 300V+ across the outer two cap terminals (the terminals _not_ jumpered together).

I don't have the same daughter board you have but here's what I see in your board:
1666803526457.png
 
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It just ramps up and holds with the yellow wire off. With a new diode of similar spec's installed it seems like it tries to fire but doesn't build voltage. I'm going to order a replacement diode of the right type and see. I am starting to think the capacitors are failed.
 

RS485

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Just to be clear - are you saying that with the new diode you have, and with the yellow wire back in place, that it ramps up? (also, you should be able to steal one of those diodes from another junk PS -- they're _very_ common in Whelen's boards)
 
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Just to be clear - are you saying that with the new diode you have, and with the yellow wire back in place, that it ramps up? (also, you should be able to steal one of those diodes from another junk PS -- they're _very_ common in Whelen's boards)
No, with the yellow wire off it ramps up indefinitely. With the yellow wire on and no diode it makes a very quiet noise in "rhythm" with the flash pattern. With a new (incorrect size) diode installed with the yellow wire connected it tries to ramp up and "discharges" very quietly, you can hear a clicking in any bulb you attach. I will harvest the right diode and see how it goes before messing with capacitors.
 

RS485

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Sound like you're on to it! If you can hear a click in the tubes, that certainly implies the timer and trigger are doing their job...but at the end of the day, there just isn't enough voltage in the caps to achieve flash...as it's probably leaking close to the rate its charging.

You _might_ be able to recover the caps. We discussed it somewhere before -- I had a PS that wouldn't develop more than ~127 volts on the caps. After at repeatedly charging for a few secs...then waiting, for what seemed like hours, the caps returned to holding +400V and the unit flashed quite robustly.

It will be a pleasant surprise for me to learn the correct diode improves anything 'cause I'd learn something...but its protective in purpose so...I'll be surprised if it helps :)
 
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Sound like you're on to it! If you can hear a click in the tubes, that certainly implies the timer and trigger are doing their job...but at the end of the day, there just isn't enough voltage in the caps to achieve flash...as it's probably leaking close to the rate its charging.

You _might_ be able to recover the caps. We discussed it somewhere before -- I had a PS that wouldn't develop more than ~127 volts on the caps. After at repeatedly charging for a few secs...then waiting, for what seemed like hours, the caps returned to holding +400V and the unit flashed quite robustly.

It will be a pleasant surprise for me to learn the correct diode improves anything 'cause I'd learn something...but its protective in purpose so...I'll be surprised if it helps :)
Yeah, I don't think the specific diode will matter. It's just there there as a backfeed to ground protection essentially from what I can decipher. It seems like the power supply is pretty much now functioning with the exception of the proper voltage. I will see if I can recondition the capacitors after I properly solder a diode on permanently.
 

RS485

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Aug 5, 2019
253
Central MA
Yeah, I don't think the specific diode will matter. It's just there there as a backfeed to ground protection essentially from what I can decipher. It seems like the power supply is pretty much now functioning with the exception of the proper voltage. I will see if I can recondition the capacitors after I properly solder a diode on permanently.
FWIW, I just replicated your experiment of detaching the yellow wire from the same side. My PS functioned exactly the same as it did before (working exactly as expected). Nice robust flashes...known "good caps".
 
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JohnMarcson

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May 7, 2010
10,337
Northwest Ohio
FWIW, I just replicated your experiment of detaching the yellow wire from the same side. My PS functioned exactly the same as it did before (working exactly as expected). Nice robust flashes...known "good caps".
It almost seems like the sides are redundant. I will steal a diode, reconnect everything and see what capacitor conditioning does.

"Diode D2 is connected between the base of transistor Q1 and the negative side of the DC power source to protect the base-emitter junction of transistor Q1 from the reverse voltage induced in feedback winding."

So with that missing it works better than with that in place and failed (ie serving as a wire vs. a diode). That makes sense in my head. Removing it makes the supply rely on "the other side" essentially, whereas with a bad diode in place it is essentially acting as as a "two way" wire vs. a "one way" diode to ground. With the bad diode removed the supply is behaving like it isn't reaching voltage, vs. full on failure.
 
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JohnMarcson

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May 7, 2010
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Northwest Ohio
That looks like an amateur attacked it with a cold soldering iron...
I assume they did, the supply "box" was un-riveted so I'm guessing that was a repaired area. The clear film Whelen put over their boards and solder makes a mess when repaired. I tried to clean it up a bit so I can solder on a new diode.
 
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RS485

Lifetime VIP Donor
Aug 5, 2019
253
Central MA
Here's a repair I did a while back on an 8000 pie-pan with beehive optic.
FWIW, "MG Chemicals 8310A - Conformal Coating Stripper Gel" came in pretty handy in taming the crusty conformal coating.

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Extracted and cleaned up AEI-219:
1667046364217.png
 
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JohnMarcson

Site Founder
Original poster
Administrator
May 7, 2010
10,337
Northwest Ohio
Here's a repair I did a while back on an 8000 pie-pan with beehive optic.
FWIW, "MG Chemicals 8310A - Conformal Coating Stripper Gel" came in pretty handy in taming the crusty conformal coating.

View attachment 240178
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Extracted and cleaned up AEI-219:
View attachment 240186
Wow, that is crusty. I'm impressed the coating could be tamed. Wait for late night and daytime TV to have ads saying "If you used MG Chemical Stripping gel around 2020 and got cancer, you could be entitled to financial compensation." I am amazed how well that works, something that good has to be super toxic.
 

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