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Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Both of them appear fine, the resistor at a nominal 6850 (6.8k) ohms, and the capacitor is not conducting. Inserting the large cap improved performance a little bit, maybe up to 4 or 5mm now. As I was checking the other capacitors, I noticed that they seemed to conduct, but only because the transistor they were near was providing a path for the electricity from my ohm meter to flow. Is this normal? Sorry for my lack of understanding on how transistors work, I'm working on that.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
hi.. well the method i used to determine my globe was up to air was to obtain a small piezo spark generator and apply its needle to the globe. Result:- no visible glow even in a dark room. On my test globe it produced a blue-green flash with volume of around 1cm inside the globe.
Another idea is to put a small cold cathode fluorescent near the driver, it should glow nicely if the circuit is working. Plasma globes do seem to have a critical current, below which nothing happens (I tried a CCFL driver and it wasn't beefy enough) hope this helps, -A
Registered Member #1153
Joined: Mon Dec 03 2007, 07:27PM
Location: Croatia
Posts: 213
Firefox wrote ...
Both of them appear fine, the resistor at a nominal 6850 (6.8k) ohms, and the capacitor is not conducting. Inserting the large cap improved performance a little bit, maybe up to 4 or 5mm now. As I was checking the other capacitors, I noticed that they seemed to conduct, but only because the transistor they were near was providing a path for the electricity from my ohm meter to flow. Is this normal? Sorry for my lack of understanding on how transistors work, I'm working on that.
For me sounds like the step down transformer or diodes in it died.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
Having little practical experience here, allow me to inject two suggestions.
First, the steadily climbing resistance of the transistor. Sounds like internal capacitance, or a nearby capacitor you might not be paying attention to (I can't see your schematic, photo hosting sites are blocked here) .
When power is first applied to a capacitor, it appears in a DC circuit as a dead short, and climbs to near infinite impedance as it approaches the input voltage (then appearing as an open). Attaching your DMM probes in resistance mode to a capacitor (or anything with appreciable capacitance) will show exactly this result, since most meters use either a straight DC signal, or a pulsed DC signal to measure resistance. Due to the fact that DMMs use a very small signal to do said measurement, in all but the smallest capacitors this can result in a slow increase in resistance. If there's additional in-circuit impedance to further slow charging, it can be drawn out over several seconds.
As for the sporadic arcs before an apparent shutdown. It sounds like you might have an intermittent short. There are three possible places for this to happen (normally). Either in the secondary winding of the HV transformer, or in a *nearly* toast capacitor in the output stage would be my first thoughts. Both can be capable of functioning at lower voltages, and only exhibiting a failure state at high tension. The other possibility is tracking along the PCB or the enclosure, which again may not occur at lower voltages.
Registered Member #5357
Joined: Sun Jun 17 2012, 01:45PM
Location:
Posts: 2
Firefox wrote ...
I was over at a friend's house today when I spotted an old plasma globe in the corner, all dusty and neglected. Of course, I couldn't let that wonderful piece of HV hardware go unnoticed, and asked him why he didn't have it plugged in, and he said it was broken. So I plugged it in, and sure enough, I got one or two thick, fairly bright solid streamers to the glass. Knowing what it should look like, I knew this wasn't right, and I heard some whining from the step-up board.
Now that I have the thing home and taken apart, I found its a simple TL494 driver into a mini AC flyback transformer. The vacuum in the globe seems fine, as the driver board got the same performance with a burned out light bulb. I found one of the transistors gives a resistance reading of close to zero (or even negative) and then slowly works its way above my multimeter's range, about 2Mohms. Is this an indication of its failure? Also, there seems to be a place for a large polarized capacitor next to this transistor, could it be possible that this cap was left out accidentally? All of the caps give a infinity reading on the meter, and the resistors give nominal resistances. I would like to repair this thing, as it seems nothing is terribly wrong with it. It also seems like it would be a fun thing to drive a CW multiplier off of.
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Plasma Globe Repair
