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  #81  
Old 10-25-2008, 03:25 PM
VW cat VW cat is offline
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GWIZ and RancherBill,
Both the Exetech and Viot meters look good. I've been getting bug-eyed searching meters. I think Home Depot has Exetech so I might go there tomorrow just to see one, and check out a few other stores. Pretty tempting to bid on the Viot though.

We've been having some trouble getting some good pictures with my son's new camera so we went back to the old 2 megapixel camera and had to make do. Looks like there have been several repairs; one diode, if that's what I've been circling , is discolored a bit. Wish there was a way to test it with it in place. Sorry we didn't notice anything until now, every component on that board seems to have a different color. Pics are 1. bottom front left 2. bot front right 3. bot right rear 4.top front left 5.top front right. Phil
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Last edited by VW cat; 10-25-2008 at 03:36 PM. Reason: added descriptions, spelling
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  #82  
Old 10-25-2008, 03:27 PM
VW cat VW cat is offline
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Last pic. Top rear right. Phil
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Last edited by VW cat; 10-25-2008 at 03:35 PM.
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  #83  
Old 10-26-2008, 03:09 PM
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GWIZ GWIZ is offline
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Quote:
Looks like there have been several repairs; one diode, if that's what I've been circling , is discolored a bit. Wish there was a way to test it with it in place.
Sorry we didn't notice anything until now,
every component on that board seems to have a different color.
Well, that puts a hold on the IGBT's.

The diodes are diodes but more then likely "Zener diodes".

Those diodes do not change color when they normally go bad.
The IGBT's may have fryed them, back feeding power back into the diodes.
In other words any color change means they are Bad.

Its not looking good.
Get the numbers off the diodes an let me know what they are.
Do not assume all the numbers are the same. what's that 16 diodes ?

Last edited by GWIZ; 10-27-2008 at 02:56 AM.
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  #84  
Old 10-27-2008, 06:18 PM
VW cat VW cat is offline
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GWIZ,
I took the board off today and brought it inside. Using a lens out of a scraped microscope I got 2 numbers off the 16 diodes: 1) MK 1N 47 44A 913 2) MK 1N 47 44A 804 - the letter M has a circle around it. My son could actually see these #'s just fine without any help.

The only way to see all the numbers is to remove these diodes, they seem to be soldered in place with the number down. I believe there are several 913's, and 804's and my son said they may be used in pairs.

I was also think that the 'bridge' of solder repair, is actually replacing a pathway the board already had(see pic). All the diode pairs are connected by a short pathway, only at the end that has the black band. The rest of the diode is a silver color.

Phil
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  #85  
Old 10-28-2008, 12:13 PM
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GWIZ GWIZ is offline
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The part number is 1N4744, the other numbers are more then likely date codes. the M with a circle is Motorola.

The 1N4744 is a 15 volt 1 watt Zener diode.

===
The Maximum trigger voltage for the IGBT's is 20 volts.

The 15 volt zeners are configured to prevent more then 15 volts from feeding into the IGBT's control lines.
anything above 15 volts will be clipped by the zeners, in this case it helps prevent any voltage spikes above 15 volts from damaging the IGBT's.

===
At the start I was trying to avoid doing any test on the driver board, sometimes you can make things worse.. obviously it had quite a bit of power fed back into it from the IGBT's.
At this point I don't see how we can make things worse, in less we do some thing stupid.

The plan is, we replace ALL the zeners and try firing up the welder WITHOUT the IGBT's and check for a trigger voltage to the IGBT's
It may tell us something or it may not without the IGBT's. your meter may not read fast enough to display anything.
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  #86  
Old 10-28-2008, 07:09 PM
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Here you go, 1N4744.


http://cgi.ebay.com/20-pcs-DIODE-1N4...QQcmdZViewItem
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  #87  
Old 10-29-2008, 05:49 AM
VW cat VW cat is offline
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GWIZ,
I'm ordering them this afternoon, soon as the first born comes home from work. That was fast GWIZ, I've got that optimistic feeling back. Is 20 enough? Thinking of any problems that might arise. We have some similar boards from scrap welders to practice soldering on. I think I will have to get a pencil soldering gun?

I picked up a local cheap clamp-on a few days ago, 'Mastercraft'. Made in China.It was $59 and they have a 60 day return policy, as long as I keep it in the package. The spec's for DC A: 400A(range) 100ma(resolution)
+- 3%rdg +5dgts(accuracy). What do you think GWIZ? Phil
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  #88  
Old 10-29-2008, 07:38 AM
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I don't have a clue what you guys are doing although I have a tech that does. I have still been following this thread and the photo through the glass is impressive. Good luck.
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  #89  
Old 10-30-2008, 03:36 AM
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Quote:
VW cat
"I've got that optimistic feeling back."

What can I say I'm a pessimist. wait a minute, am I the only person that thought you could fix your other welder.
At this point we don't have anything to lose, as long as you respect electricity.

"Is 20 enough? "

I think so. you need 16 Zeners, ASSUMING they are all the same.
that gives you 4 extra.

=
"Thinking of any problems that might arise."

Yes, but I'm a slow type'r. or is that type-or.

=
"We have some similar boards from scrap welders to practice soldering on. I think I will have to get a pencil soldering gun?"

Yep that was going too be my next suggestion, Practice makes perfect.

=
"I picked up a local cheap clamp-on a few days ago, 'Mastercraft'. Made in China.It was $59 and they have a 60 day return policy, as long as I keep it in the package. The spec's for DC A: 400A(range) 100ma(resolution)
+- 3%rdg +5dgts(accuracy). What do you think GWIZ? Phil"

I assume that's $59 Canadian money, maybe $47 US.
After seeing the exchange rate from Canadian to US $ and the shipping from the US. It may be Ok for a start.

Just make sure it measures DC amps, I don't see a position on the knob for amps or a zero set knob/button.
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  #90  
Old 10-30-2008, 03:39 AM
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Quote:
Originally Posted by OLD MAN View Post
I don't have a clue what you guys are doing
That makes three of us.
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