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ArcticMyst Security by Avery

RF excited CO2 lasers

Hemlock_Mike

Hemlock_Mike

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Cyparagon said:
[quote author=Hemlock Mike link=1228715005/180#185 date=1233894954]The movie was made in ~ 1968............   NEVER mention her name again.
Click to expand...

Jesus was made in ~0. NEVER mention his name again.  ;)[/quote]

Bless you -- I won't. For you.

Mike
 





Event_Horizon

Event_Horizon

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I don't have any sort of AC test equipment other then a couple DMM's. Not even an oscilloscope :( I understand DC circuits completely but high frequency AC stuff has pretty much left me in the dust. All I know is the transistor didn't overheat because it was mounted on a huge heatsink at the time.

I've asked Chris but I have yet to get a reply, I'll send a PM to Nightstick like you said, perhaps he can help me.

My DMM has a transistor test mode for little 3 pin transistors, but the one on the board has 4 pins. Could I somehow test it that way or is it completely different...?

EDIT: I found the datasheet for the transistor in question, found the pinout. I tried it on my DMM and the Hfe was off the scale, and also caused the low battery light to come on as well (even though it isn't low and goes off when I take it away). Resistances: collector to base is 700 ohms, collector to emitter is 700 ohms, emitter to base is 21 ohms.

EDIT 2: DC Voltages: Collector to emitter 11.8V, collector to base 11.5V, base to emitter 0.2V. AC Voltages: 0 all over. Assuming that transistor is meant to amplify AC signals, having only DC voltage across it means what? Am I looking at a failed capacitor somewhere? The more I find out, the more questions I have...

Those numbers mean anything to you guys?
 
Event_Horizon

Event_Horizon

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Thanks for the help guys. I guess it is the transistor then. I'll see if Chris has any extra and if not I'll need to track some down.

I just had a thought. The transistor is an NPN transistor. I just so happen to have some 2N3904 NPN general purpose transistors. Granted, its rated for 200mA maximum, but in theory, I should be able to connect it to the board where the existing transistor is, and if it smokes/catches on fire/explodes violently that means that it's is indeed the transistor that failed and not the driving electronics, right?
 
lasersbee

lasersbee

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Event Horizon said:
Thanks for the help guys. I guess it is the transistor then. I'll see if Chris has any extra and if not I'll need to track some down.

I just had a thought. The transistor is an NPN transistor. I just so happen to have some 2N3904 NPN general purpose transistors. Granted, its rated for 200mA maximum, but in theory, I should be able to connect it to the board where the existing transistor is, and if it smokes/catches on fire/explodes violently that means that it's is indeed the transistor that failed and not the driving electronics, right?
Click to expand...

What is the shape of your blown NPN transistor... :-?
What is the part number on your blown transistor... :-?

From what I've read on the previous posts the Blown Transistor was mounted on a
huge Heat Sink (that is because there is a great deal more than 200mA that is going
through it)... ::)

A 2N3904 will not work for more than a pico-second before exploding...IMO


Jerry
 
lasersbee

lasersbee

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Event Horizon said:
I don't have any sort of AC test equipment other then a couple DMM's. Not even an oscilloscope :( I understand DC circuits completely but high frequency AC stuff has pretty much left me in the dust. All I know is the transistor didn't overheat because it was mounted on a huge heatsink at the time.

I've asked Chris but I have yet to get a reply, I'll send a PM to Nightstick like you said, perhaps he can help me.

My DMM has a transistor test mode for little 3 pin transistors, but the one on the board has 4 pins. Could I somehow test it that way or is it completely different...?

EDIT: I found the datasheet for the transistor in question, found the pinout. I tried it on my DMM and the Hfe was off the scale, and also caused the low battery light to come on as well (even though it isn't low and goes off when I take it away). Resistances: collector to base is 700 ohms, collector to emitter is 700 ohms, emitter to base is 21 ohms.

EDIT 2: DC Voltages: Collector to emitter 11.8V, collector to base 11.5V, base to emitter 0.2V. AC Voltages: 0 all over. Assuming that transistor is meant to amplify AC signals, having only DC voltage across it means what? Am I looking at a failed capacitor somewhere? The more I find out, the more questions I have...

Those numbers mean anything to you guys?
Click to expand...

Put your meter on the resistance scale (Ohms)...
Take the transistor out of the circuit....

Take the Black lead and put it on the Base of the transistor...
Using the Red lead test the Emitter and note the reading
Using the Red lead test the Collector and note the reading

Now take the Red lead and put it on the Base of the transistor
Using the Black lead test the Emitter and note the reading
Using the Black lead test the Collector and note the reading..

Let me know what you get...
Still need the Data Sheet or the Part number... :cool:


Jerry
 
Event_Horizon

Event_Horizon

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Whew, what a ***** it was getting that thing outta there!

Take the Black lead and put it on the Base of the transistor...
Using the Red lead test the Emitter and note the reading  ~2 Megaohms
Using the Red lead test the Collector and note the reading     infinity

Now take the Red lead and put it on the Base of the transistor
Using the Black lead test the Emitter and note the reading   infinity
Using the Black lead test the Collector and note the reading..    infinity

Sure looks alot more clear now that its out of the circuit. I suppose I should have done that in the first place.

Well doc? Can we save him?
 
H

heruursciences

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Be careful with the Rf transistor, it is VERY static sensitive. first set your meter in diode test mode and measure between the BASE and the collector and emitter, you should get 0.6 to 0.7V of drop. If you get no reading both ways swap the leads and try again. If it still reads nothing the part is bad, find out what went bad and killed it before replacing the part!

It it passes this test, Hook it in ohms between the collector and emitter- the emitter is the - side and the collector is the + side. Next apply 9V to the base through a 1K resistor the transistor with the - side hooked to the collector. the transistor should saturate and read a low ohms, usually about 0.4 to 2.

DID You should make sure your 5V power supply and 12V is regulated too?
 
Event_Horizon

Event_Horizon

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Chris, the transistor seems to have passed those tests. I got a 0.9V drop on both base to collector and base to emitter on the first test, and the collector-emitter resistance went from infinity into the negative 2 ohm range (probably because of the 9v battery) when i applied the 9V battery with the 1K resistor to the base.

Both my 12V and 5V supplies are regulated, maximum 5 amps from the 12V and maximum 2.5 amps out of the 5V.

If the transistor is not the problem then what could be the cause of this? The transistor is still out of the board, should I put it back in or are there more tests to run on the board first?

I just got back a quote on replacement transistors... $50 each with a minimum order of 10 :eek:
 
Hemlock_Mike

Hemlock_Mike

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Ebay has a guy selling this transistor for $66 +s/h.  He also has a make offer line too.
I looked at the data sheet and 36 volts appears to be absolute max Vce.  Looks like it's more rated for 12 to 18 volts.  Just something I noticed. This must be the driver transistor you have there.

Mike
 
H

heruursciences

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Your transistor is OK, It may be a grounding issue, make sure all the power supplies share a common - ground
 
Hemlock_Mike

Hemlock_Mike

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Chris -- Wish I had thought of that  ;)   RF circuits and grounding everything.  
Check ground continuity through all the circuits.

Mike
 
Event_Horizon

Event_Horizon

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I am thinking you might be right. I put the transistor back on the board and I noticed that it seems like the circuit isn't getting the +5 volts from its supply. If I use seperate 5V supplies for the board and for the pwm, I can see that the board doesn't draw any current at all whether the pwm is connected or not. The 12V part of the board draws 15mA when pwm is not connected and 60mA when it is, and the pwm itself draws about 40mA. But the 5V draws nothing, leading me to believe there must be a broken lead or something somewhere.

Now, the power supply is indeed outputting 5V and there is 5V across the 5V input on the board and ground on the board.

I've already checked my ground connections and they are all joined, so I guess I am going to have to take the multimeter and start doing continuity tests of everything in the 5V circuit on the board.
 
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