Help, Ar PSU woes (different laser from last post)

SOOOOooo Earlier today Dark_Horse came by the house to check out my Argon lasers. Naturally, the first one I pulled out was my working cyonics/uniphase laser. I got it all plugged in and turned out, let it idle for a few then added some current to show the brightness. I took it up to 10A and then right back down. A minute or so later I went to turn it back up and it blew the breaker. This is pretty common with my laser, as the whole setup can draw up to 17A and it's only on a 15A breaker, along with a couple other household electronics. Well, I fixed the breaker and went to turn it back on, and the breaker blew right away. As soon as I hit the power switch the breaker blew. The fan didn't even turn an 8th of a turn, thats how quick it was. I figured the outlet or breaker may be bad, so I moved the setup to my 'trusted' location, where I constantly run the laser with no problems. Same thing. Breaker blew instantly. HHmmmm.... I was really hoping it wasn't a problem in the head of the laser, so I disconnected the head and tried just the PSU by itself. Same thing, breaker blown instantly. SOOO at least I've narrowed down the short or whatever it is to the PSU itself.

So, I'm going to perform some exploratory surgery on the power supply, and I was just wondering what areas I should be checking for common problems. This laser has run flawlessly since the day I got it, and today was no different until it blew the breaker. When the breaker blew I wasn't even up to full power yet, so I think the problem in the PSU caused the breaker to blow, not the high current draw of full power.

So, again, tips on things that are most likely to cause problems? Thanks in advance for the help!!!

I think my poor laser got jealous ever since the new argon came into the house. ;D     Either that or Dark_Horse is just bad luck  


Oh one last thing, how long should I let the PSU sit without any power in it before opening it up? I really dont feel like discharging all those caps through my body

Re: Help, Ar PSU woes (different laser from last p

Gus -- I think that PSU has a switching power supply. I'd first check the input rectifier and filter caps. If it blows like that -- I'd start at the input circuits.

Mike

Re: Help, Ar PSU woes (different laser from last p

I took the cover off and looked around a bit. There's nothing SUPER obvious that I can see. I cant see any leakage around the big caps, but then again since it just blew today it would take a while to leak out to the edge of the caps. I know the short is on the a/c side, because I imagine if it were on the DC side, the failure could have been a bit more dramatic... like maybe some smoke or at least a burnt smell or something other than just the breaker popping. I've been tracing the wires as best as I can (its pretty packed in this thing), I think the short has to be on the board side, like where all those big filter caps are, since the straight AC that branches off to the head still worked, since the fan moved a bit.

I guess one of these nights I'm really going to have to tear into this thing to solve my problem since I just cant see enough with everything packed in there. Any more help would be greatly appreciated. Also if anyone knows any tests I can do to single things out that would be great.

Re: Help, Ar PSU woes (different laser from last p

Anyone else? I guess I'm just going to start digging into it.

Hey Mike, do you know if the big transformers ever go bad in these? And if they do would they cause a short like this? Right now I'm pretty fixed on the fact that it's probably a capacitor but I really don't know what else to look for :-[

Re: Help, Ar PSU woes (different laser from last p

Check the cord fort shorts and innards of the PS for loose screws shorting the mains- you're right DC side failure is pretty scary to say the least in argon PSU's

Re: Help, Ar PSU woes (different laser from last p

Gus ---

What Chris said -- I looks to me like a primary input fault. Those input side filter caps can take a helluva whack when turned on. They may not show leakage (seldom).
1. Use an ohmeter on the power input. Look for low ohms line to neutral and line to ground.
2. Check the input diodes for a shorted diode. That's a major short into the caps.
3. The transformer is a high freq isolation device and they seldom fail.
4. The laser never has time for the ignitor to fire because of delays. This is why Chris and I feel that it's an input short.

Mike

Re: Help, Ar PSU woes (different laser from last p

Hemlock Mike said:

Gus ---

What Chris said -- I looks to me like a primary input fault.  Those input side filter caps can take a helluva whack when  turned on.  They may not show leakage (seldom).  
1.  Use an ohmeter on the power input.  Look for low ohms line to neutral and line to ground.  
2. Check the input diodes for a shorted diode.  That's a major short into the caps.
3. The transformer is a high freq isolation device and they seldom fail.
4. The laser never has time for the ignitor to fire because of delays.  This is why Chris and I feel that it's an input short.

Mike

Click to expand...

I'll elaborate on this a bit when I get back (I had some more time to tinker today) but is it possible for the switch itself to short? Also I checked the big caps and none showed shorts, but I didn't check the diodes. Update in a few minutes... girlfriend is bugging me to come to dinner :

Re: Help, Ar PSU woes (different laser from last p

Sex interests before lasers ?? OMG ;D ;D
And what's this about food before lasers ........

Mike

Re: Help, Ar PSU woes (different laser from last p

Chris at Heruuretc ----

If you are looking ---- Can a power supply be turned on without the head? It my not power up but shouldn't blow fuses.

Mike

Re: Help, Ar PSU woes (different laser from last p

OK Gus ---

I took the chance. I powered up my ML argon PS without the head.
It turned on the fan and did nothing as expected with no load or feedback. I powered down, let it rest and it's running now normal.

Try it without the head.

Mike

Re: Help, Ar PSU woes (different laser from last p

This whole time I've been doing it without the head connected. I don't think it's a good thing to leave the PSU on without the head since it will send a bunch of current to those cathode leads, but mine doesn't even get any power to it so it's not an issue. As soon as that fan spins and the breaker doesn't blow i'll shut 'er off ;D

SOO... I was poking around with the multimeter earlier, I disconnected the big transformer for the cathode, the board on the side of the PSU with all the small components, as well as the smaller transformer at the back right above the fan, and the short was still there. If I test for continuity across the two AC lines coming right out of the power switch, it indicates a short. The good news is that with all the 'big' stuff disconnected, the short is still there. SO it has to be something really stupid and easy. Like I said I was able to test continuity accross the big caps on the main board and they all showed resistance. I didn't get a chance to test the 'square' looking caps though, which I believe are the first ones that power go into. Also, when you say diodes, am I looking for a typical silicon diode looking thing or am I looking for something bigger? There are a series of IC's that are all heat-sinked to the major sink of the PSU, are those worth looking at?

One thing that I DIDN'T think of while I was in there, was to disconnect the main board and try to turn it on. I think when I unplug it, it will work, which will single out the main board as the issue. I'll also take some pictures so you guys can see what I'm dealing with.

Thanks again for all the help Mike and Chris. I've been stressing out about this thing since it broke, but now it feels like I'm making a tiny bit of progress in the right direction. I'll report back with some pictures and 'test results' in a few. Thanks again!!!

Re: Help, Ar PSU woes (different laser from last p

The square caps on the power input are line filters. One could be bad. Not likely but don't discount that. The main input diodes could be large to220 types with heat sink or a large square full wave pack.

The HV output should be OK with no load for now since there is no power. Remember that that capacitor bank will look like a short until charged. Are there any MOV surge supressors? One may have shorted. Any shorts to case ground?

Mike

Re: Help, Ar PSU woes (different laser from last p

Check back in like 3 minutes I'll have pics up... taking them as we speak  

Oh, and no case shorts that I could see. I traced almost every damn wire through this thing  :-[

Re: Help, Ar PSU woes (different laser from last p

Gus -- With no load, there's no current to the cathode. Just voltage.

Mike

Re: Help, Ar PSU woes (different laser from last p

Gus ----

Just a thought. One of my Ar lasers popped off the power switch if it went over temperature. It was a breaker in its own right. Without the head, could this send a shut down signal to that breaker or is it the main power breaker in the power line?
Mike

Re: Help, Ar PSU woes (different laser from last p

Here they are! The transformer is disconnected on purpose so that's not the issue, just a head up