Xenon Strobe repair

Hello,
I have an old xenon strobe (disco light) that had been stored for a very long time and when I tried to turn it on recently, it no longer worked. I first assumed it was the xenon tube bulb so I replaced it but it still does not work.
I opened it up (circuit was inside wood box) to try and measure voltage at different points to see if I could determine any current interruptions but as soon as I plugged it in, there was a point on the back of the circuit that lighted up (burning) and even some smoke came out. I immediately unplugged it.
Searching information on this I found this topic: http://www.aaroncake.net/Circuits/strobe2.asp , and it seems like my circuit is very similar. The burning came from one of the terminals on what seems to be the 4KV Trigger Transformer (see red arrow on attached photos).
I am no electronics expert (I do own and can operate a multimeter), and that is where I would greatly appreciate any support on this forum, is there a way that I can troubleshoot this circuit to get it working again? Any suggestions or ideas?
Thanks on advance for any comments.

Hi Manuel

Possibly is xenon tx or it could also be the SCR device which should fire as the small cap charges up

The voltage is then delivered to the gate of the SCR via a BR100 a diac or similar triggering device which is controlled normally via a pot to set the charge time, hence delay time btw pulses to the SCR , i.e your pulses btw light burst giving you the strobe effect

The SCR once fired dumps the charge caps big caps on the PCB through the trigger coils firing the xenon tube there should be a load resistor between the main capacitors (caps) to the xenon tube so as not to burn out the tube Normally its SCR that faults

If the print is badly burnt around the trigger coil it may just be a dry joint Scrape away the track resolder , You may have to remove the trigger coild clean up the contacts and re insert , solder , then re test

If you need another trigger coil you can buy these from Maplins Electronics

Scehmatic would help

If you want a new circuit to build Yes I have one that you can daisy chain with other strobes or I can build this for you if stuck

Mark
www.harrington.force9.co.uk
www.eeweb.com/project/mark_harrington

Sometimes dust can cause arcing, then arcing burns the PC board which carbonizes it. The carbon provides a conductive path which, basically, causes a short. The only way to fix that is to use a Dremel tool and grind out the carbon paths. Or you can drill out the areas, but be careful not to drill into the transformer. In fact, probably best to remove the transformer, remove the carbon and then re-install the transformer (depends on your skill level .

Not a guaranteed fix, but a common problem, so the prognosis is good

Another possibility is that the arcing originally occurred because the high voltage is not making it to the xenon tube (thus it is allowed to build up to the point where it can jump the gap between the Xformer terminals). So, make sure the capacitors are discharged, then use an ohmmeter to test the traces/connections between the xformer and the xenon tube. If any of them show high impedance (i.e. are open) resolder or jump them as needed. You still need to remove the carbon, though.

Thank you very much for the detailed explanation and your offer to help. I will consider your offer if I do get stuck.

Would the fact that the burning ocurred happened when I powered the circuit wihtout the xenon tube in place have anyhitng to do? There was no specific reason for doing this. The intention was to power the circuit and test for continuity at each of the elements and the tube happened to be removed at the moment.

Besides scraping away the burn, is there a way that I can test each element? Do I actually need to power up the circuit to test or could I just do this with the ohmeter?

Thanks,

Thanks Steve, I will try to grind out the carbon paths as you suggest.

Regarding your comment on the possibility of the arcing occurring because the high voltage not making it to the xenon tube, could this have happened because I powered up the circuit without the xenon tube in place? I had removed it, for no particular reason, and never thought that this could cause an issue.

How do I make sure that the capacitors are discharged? Just measiring voltage between contacts?

Thanks,

Yes, powering it up without the xenon tube could very well have caused the arching. The xenon gas, in the tube, ionizes at a certain voltage level and then becomes quite conductive. This conductive path will apply a considerable load which will reduce the voltage and thus, never let it get high enough for arching to occur.

BTW: it 's the ionization of the xenon that causes the flash of white light. As the electrons that were stripped away by the ionization process, fall back into orbit around the xenon nuclei, they emit photons -- at many frequencies across the visible spectrum, which is why it is perceived as white.

You wont lose anything by powering the unit up put it that way


9 times out of ten
Faults with are as follows

SCR
Diac
Trigger coil (rare but does Happen)
Dry Joints (possibly your case and arcing around the trigger coil pins “The same as you find on a LOPTX of a TV" )

If you have worked on tv before you will know roughly what to look for

and xenon tube Vary rare that anything else fails

I've never known anything else to fail on these

If it something else, its a strange fault
So static test resistors capacitors all rectifiers

This honestly is such a simple circuit to test its not rocket science
There is nothing in it compared to professional lighting systems these days

Ok, I scraped away the carbon area between the lines and even put some nail polish on it (I read somewhere that this was a good insulator - ???). I placed the xenon tube back in and powered up. The arcing burn is no longer there! ...however, no strobe flash.

So, I got rid of that issue (thanks again for the advice!), now I just need to get the circuit to flash that tube again.

I read somewhere that the electrolytics could be dead due to being inactively stored for such a long time, correct? If this is the case, would you recommend that I try replacing these to begin with?

The current electrolytic caps on the circuit read: 22 uF, 250 WVDC

As replacement for the electrolytic capacitors, I found these online from a local store:


Electrolytic Capacitors
The specs are:
- Radial
- Aluminum
- 22 uF, 250 Volts
- 13 x 29 mm.

I assume that these will do the job, right? Or, is there anything else that I should consider when looking for the replacement?

Would you suggest that I go ahead and replace these or would you suggest that I try to test all components first? I would not be sure of how to test these, I do have a multimeter, so any specific instructions will be greatly appreciated.

Thanks!

Its unusaul for caps to go on that circuit if it they were suspect Id expect the load resistor to be open circuit or severely burnt so i doubt it but the only cap that might have gone is the green cap on the pcb rectangular just below the diodes 1N4001


Use a DVM

First can you reverse engineer the circuit? If so do that first Not difficult on that circuit if not, time to do some measurementsIm making an effort this side buts its difficult with ought having the board in front of me

1. With the unit switched off
2. : Discharge the capacitors short the positive end to the negative end with a lead attached to a 100k resistor Measure the voltage across them to make sure they are discharged before you carry on otherwise you might get a shock even though the unit is off
3. Measure the big resistor see what your ohms reading is compare with that written on the resistor
4. Measure the potentiometer both sides with reference to the slide make sure that your ohms reading is constantly increasing decreasing without any dead spots
5. Change the Neon small glass bulb
6. finally check the scr and the feed resistor to the gate
7. If you have a scope the input to the SCR see if you have a pulse with the unit on running on isolated mains Make sure both scope and unit are measuring are running on isolated mains Ypou may even be able to check this with a dvm
8. Change the SCR if necessary
9. All of the above fail it’s the trigger coil Replace

Regarding the nail polish, consider this: what about the air above and around the nail polish. It doesn't matter how good an insulator it is, as long as there is an insulator in parallel with it that will fail before it does (and I'm, actually, not sure which will fail first) then that insulator is useless.

Also, if it ever arcs again -- will, not, the nail polish be charred by the heat of the plasmatic air, thus adding more carbon to the path?

Don't get me wrong, the nail polish doesn't hurt, but it really doesn't add anything.

Think in terms of what is unseen, as well as what is seen

Here is what I can make out from the pictures very difficult if i dont have the board

Thats your component layout I need to know what the device is the black 3 legged component on the pcb Can you read the number off it for me and quote thanks Mark

image link below
http://www.freeimagehosting.net/7tvbk

Thanks Mark.
Following your suggestions:
2 - I checked the voltage across the capacitors, right after disconnecting power, and they were completely discharged, - I guess this would either mean that there is no power reaching the capacitors from the circuit or that the capacitors are dead, correct?
3 - Is the big resistor that you mention the rectangle shaped on the side? If so, the measure seems to be right at the 200 Ohms written on it.
4 - I tested the potentiometer and the ohms reading is not constant. The middle range (about 2/3) gives no reading. I followed these instructions: "Your text to link here...(Test Potentiometer)":http://www.youtube.com/watch?v=Eh2cQCLie5A , and only the lowest and the highest parts of the whole range give out a reading. If I test between the two end poles I just get an infinite ohm reading, instead of the "reading equal to the pot's rating", as described in the video. --- does this mean that the potentiometer is bad? could this be the issue in the circuit? is there a way that I can further test this?
5 - I do not have a replacement neon glass bulb handy. Do you suggest that I do try to get one?
6 - I would not know how to check the scr and the feed resistor to the gate. Can you please explain this?
7 - I do not have a scope. Can I check this with the multimeter?

Thanks again for your help.

Thanks Steve.

Good job with the diagram!

If I understand correctly which black 3 legged component you are asking about, reads: HTEC 103B (not sure if this last digit is a B or an 8)

I made this merged picture of the front and back, in case it helps:
http://www.freeimagehosting.net/qxqec

Hi Manuel

Think we have just found you problem change the pot 3/4 of the way gives no reading right ? Means the pot is open circuit so capacitor is not charging "Green Thing" , neon not firing and no pulse to the SCR or Thyristor

You should see the neon the small glass thing next to the trigger coil flash in time with the strobe If that doesn't flash it means no trigger pulse so no 1.5 kv pulse to the xenon

The big thing on the side Yes that's a resistor rated at 200 ohm check it any way to make sure its 200 ohm on the ohms range of the meter Again make sure you have no power to the board and also double check no voltage on caps once its powered off Safety

haven't had chance to look at device yet will search today on this and see if i can get datasheet

Try what I've said first though

It is true that aluminum electrolytic can dry up over time, but no need to assume that is the case for yours. If it works, don't fix it ;)

Also, if you _do_ need to replace them, make sure the voltage rating is 250WVDC (that's _Working_ Volts DC)

Hi Manuel cant find any info on numbers quoted are there any other numbers on the device letters etc or can you find serial numbers on the pcb or something that might identify the unit or part

Cheers

Mark

Hello Mark,

Now, if the pot does give a reading at both ends of the range, when I put it at these positions then it should be sending power out to the circuit, correct? Still, the strobe is not flashing at any position of the pot.

The small neon tube is not flashing at all.

I checked the big resistor and it is reading the 200 ohm.

Any suggestions for what to try next?
Thank you.

Manuel

Hi Manual change the pot

The reading at both ends is possibly ok but it doesent mean the slider is making contact with the carbon tack. That means the cap will not charge and discharge correctly if at all ,"The green cap is what Im refering to "

Unless you can get that neon to light up at say 10 hz ,"10 cycles per second " ,"!0 Flashes per second " , the trigger coil doesent discharge via the big caps "Gold colour cylinders rated at 220uf "

So no no 1.5 to 4kv pulse to ionise the gas inside the Xenon "

Its a strange circuit anyway to be honest with you I'd be inclined to rebiuld this but at the moment change the cap first then change the neon

What you can do is remove the Thyristor or SCR
Make a note of how the black device comes out ie there will be a flat sided face to this draw it on paper so that you know which side the flat side faces on the board Top side view or component view

Sold two insulated wires to the outer points of where that device mounts into the PCB Connect this to a push button switch or bare either side


Switch the unit on and momentarily make the switch contact You should see the Xenon flash This will tell you that the Xenon is ok and the trigger coild is ok

Try this after youve done what Ive suggested

See Link below for better idea of what Im talking about
http://www.freeimagehosting.net/38d4l

Unfortnatley I cant identify or find a datasheet on your device "Typical this !! "

Otherwise me old mucker its a case of build a new one in which case Ive said Ive got a fantastic circuit for one which will daisy chain up to 200 strobes Im quite happy to make the PCB and supply parts to you at a fair price

Or I can assemble and make for you

Below is a schematic I found on the Internet that I probably the same as (or similar to) what you have. First of all, not sure what region you're in, but this circuit is probably designed for 120 VAC. If this was plugged into a 240VAC mains, that could be your problem (but it's still possible that what you have was designed for 250VAC, etc, etc,

Assuming 120VAC all around, have you tried this:

* Test the voltage across C1 -- should be around 150 to 170
* Test the voltage across C2 -- should be around 320 to 340 Volts.
* If you replace the Pot (and I strongly suggest you do) and it still doesn't work, check the voltage across C3 (this would be better done with a scope, where you would be looking for a rounded sawtooth waveform). If the meter reads in the neighborhood of 300 volts, then the neon light or the SCR (or both) are bad. To test the Neon light (this will only work if there is, indeed, ~300V across C3), CAREFULLY [i.e. discharge C3 first -- perhaps with that same 330K resister] connect a 330K resistor from the gate of Q1 to the Cathode of Q1, if the neon light glows, then it's probably OK and the SCR is bad.

Oops, forgot the diagram...

Also, I'm assuming you know how to behave around high voltages -- if you don't, step away from the strobe light -- immediately!. Just saying to cover my A$$

I had a look at the schematic , not the same steve roughly but not the same I partially reversed engineered the diagram and its difficult to determine whats being used a Thyristor or Scr

In fact they seem to split the voltage across the smoothing caps but dont run the SCR or Thyristor down to ground or Zero volts Very strange circuit they are using here

I remember a bloke working on something similar to this over at Di Di's Elham SE9 In fact it looks rather familiar I seem to recall he had similar problems he couldnt get this to work at all No matter what he tried a competant engineer so Im assuming this is the same model recalling from memory