Printed circuit board failure

Question

I have a miller welder that blew some resistors and a voltage regulator on 2 boards. I can buy new boards but that's around $2,000. the resistors are burnt to the point I don't know what size they are. I've tried contacting Miller Electric but they told me they can't send me any info on the boards. Can anyone help me with this? I don't know a lot about electronics. Part numbers for the two boards are 207818 PC2 and 200841 PC10.

dougw · Answer

The damage in the bottom picture to the resistor and Q11 are not from a little gentle overload - they look like massive catastrophic overload - as in perhaps mains voltage got shorted across them. Simply replacing these components will not fix the reason they blew. You need to track down where the high current short occurred and fix that too.

If you trace out the circuit, you can often deduce what the resistor values should be.

Have you tried measuring the value of R6 and R7 - they may still be somewhat intact.

If my mage enhancement is accurate, there may be a couple of blown transistors on the top card as well?

D4 also looks stressed?

jw0752 · Answer

Hi Billy.

If you know anyone else with one of these units perhaps they would give you a quick look so you could note the color bands on their resistors. Other than that, like dougw said there are going to be other problems that are not as visible as the blown resistors. Do you have any insights into what happened just prior to the smoke and fire?

John

dougw · Answer

The damage on Q11 probably caused that noise. Thermal expansion stress due to very rapid localized increase in temperature (as a result of excessive current) causes the chip package to explode. The onset of high current needs to be very sudden for the exterior to still be cold when the inside reaches a high temperature.

The resistor that evaporated might have made a noise too although I've smoked lots of resistors without generating much noise.

bd467 · Answer

Nick send me your email address. I can send you all the pics you need to replace your parts.

jw0752 · Answer

Hi Billy,

Your Q11 number corresponds to an IG4PH50UD which is an Insulated Gate Bipolar Transistor with an Ultra Fast Recovery Diode. Here is a link to the Data Sheet if you want more information.

http://datasheet.octopart.com/IRG4PH50UDPBF-International-Rectifier-datasheet-561823.pdf

It is likely that the IG4PH50UD took out the resistors so if we can determine what the values of the resistors are it would be worth your while to at least try to replace the IGBT and the resistors and give it a try. If the new board is $2000 it is really worth a try.

bd467 · Answer

Here's what I got last night. I'm thinking R8 is the same value as R105, R106 and R4. I hooked my multimeter up and got the resistance. I was also thinking R7 is the same value as R6 based on the resistance being the same. R108 looks stressed as well. I'm willing to try and repair these boards. based off the color bands what resistors am I looking for. my eyesight isn't the best but R8 looks like red black black red brown 20kohm 1% is that correct? R108 Orange red black black brown 320ohm 1%. R6 I'm not sure on the colors. I'm using a resistor calculator I found online. Feed back please and where can I buy these.

bd467 · Answer

John I don't know anyone with the same welder. I've searched the internet for pictures of the boards with no luck finding anything. Just before the smoke there was a loud bang, sounded like a gun shot and then smoke.

bd467 · Answer

Q11 G4ph50ud

rollinsparta · Answer

I have the same boards in my welder; it's a Dynasty 200 made in December 2007. Bought it yesterday knowing it didn't work with the intent to get it running. So far, I have taken off the cover and am in the middle of visual analysis/prepower testing. I have those same 2 resistors burnt below r108. Also my resistor r6 is burnt near q11 on pc2 207818. Let me know if you need any more pictures/specs. Mine is missing r24, r27, c14, and c15 on pc2. Can you send me pics/specs of those? Thanks!

bd467 · Answer

Sent from my iPhone 
 Attachments:

bd467 · Answer

I followed you. I've gotten all the resistors changed out and all the parts that looked bad but when I did my pre power check D2 diode is showing bad. Got a new one on order. Hopefully that fixes It. So far I'm into the repair for $30. My email is insanefab@hotmail.com

lanuser · Answer

Let me know if you still interested. I have all neceseryinformation for you if you needed. Just don't want waste time on 3 yer old post. Thanks.

jw0752 · Answer

Hi Billy, If you still have the piece that chipped off Q11 it may have some marking that would help identify it. John

jw0752 · Answer

Hi Billy, You can reply to your own post as you have been doing and the tool bar should give you the option to insert more pictures. John

dougw · Answer

Note that the resistance measured with the resistors still connected in the circuit may not be accurate. To get an accurate measurement you may need to unsolder one end.

bd467 · Answer

Forgot to upload this one. This is the resistor by Q11.

fixingthings · Answer

One item you may want to look at is the service manual for the Miller Dynasty 200. This service manual is actually the “Technical Manual” which just became available on eBay today, so I purchased one. It is older than your unit but may help in troubleshooting your welder. One caution is that lethal dangerous voltages surround the electronics on the inside of your welder. Components may explode when the unit is powered up due to failed components. i also purchased the Dynasty 200DX. No components are burnt up physically. When I power it up, there is no hum, no clicking “on” of the relay on the inverter board, and the front panel display is dead. I’m not sure why there is no voltage on some connectors. It may just be the input/pre-regulator inverter module. I don’t want to replace it unless I know it is bad. Miller4less has it for $312.61. Hopefully this service/technical manual will help me out. If anyone knows where I can find a “Testing Booklet”, that would be much appreciated.

dougw · Answer

Yes, I mean measure the resistance of all the resistors. your low cost meter should be adequate at this stage.

Printed circuit board failure

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