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Dynasty 200SD low buss voltage

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  • jjohn76
    replied
    Updates of the issues I found in the bootstrap power supply and the control boards' power supply. This board is completely removed from the welder and no mains power is used directly because there's no need to risk electrocution.

    The bootstrap power supply provides 15V to the controller that manages the 30V on the control boards'power supply (this 30V feeds every board, directly or indirectly). It does this by connecting a 150k ohm resistor array (the one in the previous post) in series with a 15V zener diode across the DC buss (there is a little yellow filter cap across the zener diode to smooth out the 15V). So long as the buss voltage is above ~17V DC, this circuit provides 15V. Everytime the power switch goes on, the DC buss charges to somewhere between 162V DC and 325V DC (the peak voltage of the incoming 120VAC RMS and 240 VAC RMS).

    My zener diode was bad, measured by a multimeter diode tester and also confirmed by putting 30V DC across the DC buss from my power supply. Replacing this zener diode now has 15V going to the control boards' 30V power supply controller on PC10.

    Click image for larger version  Name:	IMG_20191005_084118610.jpg Views:	0 Size:	56.0 KB ID:	602938 You can see the carnage on this board, with the big hole in IGBT Q11 on the left and R6 in the center. Those are part of the 30V power supply and I'll fix later. Right now, I am working on the 15V bootstrap power supply, which relies on D2 (15V zener diode) and C2 (.1uF filter capacitor) to give a stable 15V to the 30V power supply controller.
    Click image for larger version  Name:	IMG_20191005_084940093.jpg Views:	0 Size:	42.2 KB ID:	602939 There are a couple ways to check zener D2. Using the diode tester on your multimeter lets you know whether or not it is shorted. I didn't get a picture of that (not enough hands), but here's how I also test it. I put 24V across the DC buss (+ fed into the top portion of the resistor array on yellow clip, - connected to pin RC2-2 on hard to see black clip) on PC2. Anything other than 15V +/- tolerance listed in the datasheet and it's not working right. This one was shorted, so it showed 0V.
    Click image for larger version  Name:	IMG_20191005_100404593.jpg Views:	0 Size:	57.9 KB ID:	602940 I removed the zener, checked to make sure the board still wasn't shorted across the test points (that would have indicated C2 was likely bad too). Then put the replacement back in. It now shows ~15V across the zener, so we're good to go. I'll check later to make sure the cause of the bad zener wasn't something on board PC10.
    Last edited by jjohn76; 10-05-2019, 12:22 PM.

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  • jjohn76
    replied
    So with the Maxstar 200DX good enough for my buddy to abuse/test, I moved on to the Dynasty 200SD. I still don't know how deep the problems run, but just started down the control boards' power supply chain. Before starting that thread, I wanted to compare the boostrap supply resistor arrays between the earlier Maxstar 200 (above) and the later model Dynasty 200. Besides the additional standoff/spacing between the board and resistors I mentioned a couple posts ago, the newer board also has a lot more copper around the resistor arrays pads. Clearly those resistors were putting too much heat into the board, and Miller's design solution was to use more of the copper trace to absorb some of the heat. These 3W resistors are very small compared to other resistors of the same power ratings, I guess it's because they conduct a lot of that heat away from the body into the copper traces. This same issue exists on the clamp board in my Dynasty DX, and I don't remember how much time I spent (wasted) trying to see what was causing the over current through the resistors. Turns out to just be bad thermal management design from my perspective...

    Click image for larger version  Name:	IMG_20191005_065751968.jpg Views:	15 Size:	29.7 KB ID:	602935 Here you can see the shadow of the large copper pads underneath the bootstrap power supply resistor arrays.

    Click image for larger version  Name:	IMG_20191005_065655777.jpg Views:	14 Size:	27.8 KB ID:	602936 Here is the underside of the board showing those same large pads...
    Last edited by jjohn76; 10-07-2019, 09:27 AM.

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  • jjohn76
    replied
    Update - I had enough capacitor lead left to solder the Snubber back together. I just ran a half dozen 7018 1/8" rods on a scrap piece (would show the piece, but I welded over test beads from a Haas-Kamp project it looks terrible). The fan kicked on a couple times and no issues.

    My only concern is a buzz/squeal when the machine is on when not loaded. There is a quiet buzz coming from both input inductors (boost inductor and snubber inductor) that turns to a quiet squeal when I close the contactor, and even higher pitched to unnoticeable once I load it, either crowbarring the output (3' steel piece between leads, run amperage from 1 to 200) or running rods. I haven't put any scope traces across the DC bus or inductors (yes, I use differential probes to avoid electrocution or magic smoke from my oscilloscope), not sure if I need to or would know what the switching spikes should look like. The output waveforms match the ones in the technical manual. Any thoughts?

    Here's what it looks like back together. I think I am going to leave it looking like this, except cross out the yellow N and replace it with a K, for Kinda effing good...
    Click image for larger version

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    Last edited by jjohn76; 09-29-2019, 01:42 PM.

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  • jjohn76
    replied
    For anyone that hears a low pitched buzzing sound, particularly from the lower half (transformer output diode area), it could be that your output diodes are unintentionally hard switching... That appears to be the case on the Maxstar at least. I found a break in connection between the output diode Snubber (resistor capacitor snubber shown in the picture). I checked the output rectifier again, as well as the active clamp (diode check across all four leads, each way). There's not much lead left at all on the capacitor to resolder the connection, so we'll see how to get it going...
    Click image for larger version

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ID:	602566 This is a picture of the underside, with the output rectifier bridge on the right. The gold resistor and blue capacitor soften the hard switches when the output rectifier converts the AC voltage from the transformer to DC).

    Click image for larger version

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  • jjohn76
    replied
    Well, I received and replaced all of the parts on the Maxstar today - the two buss capacitors, the inrush circuit bypass relay, and the four 150k resistors. After reconfirming I didn't miss something in the pre-power checks, cinched everything up and turned on the power. There is a faint low pitched buzz on top of the normal high pitch hum from the inverter. All functions work and I ran a half dozen 6010 1/8" rods back to back to see how it went. The only thing concerning me now is the fan never turned on. The fan resistance checks out at 1.5M and the negative lead on RC7 (PC1) stayed open. I know it's fan on demand, but would expect it.to demand the fan at some point. When I pulled the case, nothing was beyond warm.
    Click image for larger version  Name:	IMG_20190928_144625253.jpg Views:	29 Size:	27.4 KB ID:	602550 original capacitors
    Click image for larger version  Name:	IMG_20190928_172324229.jpg Views:	24 Size:	63.4 KB ID:	602551 replacement capacitors and new orange resistors installed with 1/8" standoff from the PCB
    Click image for larger version  Name:	IMG_20190928_192943749.jpg Views:	27 Size:	34.8 KB ID:	602553 case removed after burning some rods, checked the fan voltages
    ​​​​
    Click image for larger version  Name:	IMG_20190928_181946228.jpg Views:	26 Size:	30.8 KB ID:	602552 I didn't fully seat one of the capacitors, but it seems ok.
    Last edited by jjohn76; 10-07-2019, 09:25 AM.

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  • jjohn76
    replied
    Yup, I am not an electrical engineer, or an electronics tech, so this is a steep learning curve that's only taken about a couple dozen broken welders and some broken plasma cutters to get to confusing myself and others...

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  • Sberry
    replied
    I can see I am at the still eating dirt stage.

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  • jjohn76
    replied
    Thanks Noel. Yes, this is clearly an out out control hobby... Hopefully I get to a point that is helpful for others.

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  • Noel
    replied
    I have a buddy that does cross word puzzles...What you have there is the New York Times edition. I'm thinking you both are learning new words as a result of your interests? Well done! I'm cheering for you.

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  • jjohn76
    replied
    Updates to this thread, the Maxstar PM1 passes all checks above, which includes the Snubber IGBTs. I am pretty sure at this point the capacitors have aged to the point they are drawing too much current and overheating. The photo below hopefully shows how some gas has expanded in the tops of the capacitors (the cases themselves are not bulging, just the plastic cover is blistering). With PM1 functional, I am just planning to replace the two buss capacitors - these are 50mm diameter by 80mm tall Panasonic T-UPs, which have a CDE direct replacement - 382LX152M450B082VS. Total cost for two plus shipping and taxes is $52. I will also replace the input bypass relay on PC2. The only concern I still have are the hot marks on PC2 from the R1,R2,R36,R37 resistor network on LC2. These 4 ea 3W 150k ohm resistors basically make an equivalent 150k resistor with around a 12W capacity. These are not the capacitor bleed resistors as thought in a different thread - these basically limit current in the 15V bootstrap power supply. It connects directly from the DC buss (163V to 325V at power up depending on 120V or 240V AC input, then 810V once the boost PFC circuit is engaged) to a 15V zener and filter capacitor to provide 15V to the buck circuit controller (left side of PC10) that controls the 30V supply linked to every other board. I noticed these are soldered much closer to the board on the Maxstar than the Dynasty (about 3/32" space between resistors and board shown in pictures). The buss capacitors are in series, and the bleed resistors are two each triplets of the same orange 150k resistors. These are not showing signs of overheating (like they were on the previous Dynasty), so my guess is the DC buss voltage wasn't excessive. This leads me to believe the hot spots are common on early designs and Miller incorporated the standoff on later designs.
    ​​​​​​
    Click image for larger version  Name:	IMG_20190922_173021058.jpg Views:	0 Size:	46.4 KB ID:	602429blistered top of cap, the lower right shows the bleed resistor network
    Click image for larger version  Name:	IMG_20190922_172856192.jpg Views:	0 Size:	47.4 KB ID:	602430 top side of PC2, orange resistors in contact with board on Maxstar Click image for larger version  Name:	IMG_20190922_172905435.jpg Views:	0 Size:	32.5 KB ID:	602431 heat marks on bottom of Maxstar PC2
    Click image for larger version  Name:	IMG_20190922_173100981.jpg Views:	0 Size:	42.6 KB ID:	602432Dynasty orange resistors have a bit of standoff from PC2
    Last edited by jjohn76; 10-07-2019, 09:23 AM.

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  • jjohn76
    replied
    So after selling the last one and helping the buyer swap the PM mod and PC2 from another DOA Dynasty, my buddy drops off two more welders, a Dynasty 200SD and Maxstar 200SD, to figure if I can get them running. The Maxstar has a weak input switch (apparently the weldors were holding the switch closed to keep it powered) and the buss capacitors have definitely overheated (signs of gas venting). The inrush bypass relay on PC2 (bad one shown in a picture of a different welder in first post above) shows signs of the solder connections overheating, though it still functions properly (test is in a post above).

    The Dynasty has more problems, with a short somewhere in the 30V power supply chain causing the buck IGBT (Q11 on PC2) and current sense resistor (R6 on PC2) to go. I haven't checked the buck diode (D4 on PC2), but will do that soon to see if it took excessive current. The 30V supply feeds pretty much every board in the Dynasty, directly or indirectly, so all of the boards need testing separately. We'll see how that goes. Hopefully at the end of this thread, there will be at least a bit more troubleshooting information than what is in the Technical Manual. My initial process is to check the remaining components of the 30V buck circuit (PC2 and PC10 have these), power the 30V from a current regulated power supply to PC1 and PC10 after first checking for shorts, then working my way through each board the same way.

    Edit: I don't know how I missed the thread below when last researching the Dynasty problems, but the failed snubber in the semikron module (PM1) is kind of common but tough to check. Without the snubber, the buss capacitors could likely suffer from overvoltage (810V bus across two 450V capacitors with a total surge voltage limit of 1000V). Visual/Audible clues are a low pitched buzzing sound when powered on, or signs of burnt PCB/discolored traces at the bleeder resistor arrays (two of them, they each have three orange 150k ohm resistors side by side). The PM1 check above should identify any failed component in semikron PM before anyone starts replacing buss capacitors, bleed resistors, or PC2 entirely.

    https://forum.millerwelds.com/forum/...ding-the-parts
    Last edited by jjohn76; 09-24-2019, 05:41 PM.

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  • jjohn76
    replied
    So, after replacing the relay and putting it on a current limiting circuit (a box of four light bulbs in parallel before the plug), the machine powered up. It has a very low pitched buzz sound, somewhere below mains frequency. This thing is going on Craigslist for parts...

    Click image for larger version  Name:	IMG_20190629_210509_02.jpg Views:	93 Size:	58.1 KB ID:	598576Click image for larger version  Name:	IMG_20190629_210509_01.jpg Views:	105 Size:	67.0 KB ID:	598575
    Last edited by jjohn76; 09-21-2019, 01:29 PM.

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  • jjohn76
    replied
    I spent a little more time on the Dynasty 200 today, and discovered the Snubber S1 wouldn't turn on. The pre-power checks for this require the test point between the C12/C13 midpoint, and outside of pulling PC2, I wouldn't have found the issue. The pre-power checks guide through checking the input rectifier and ensuring the inverter and boost IGBTs are not shorted and their free wheeling diodes are good. Attached is a picture of the PM1 with it's circuit connections. I believe the Snubber S1 and S2 connect XFRM2 to the common point between C12 and C13, but don't know for sure. Here is how I checked the PM1 IGBTs with an IGBT tester:
    Boost IGBT
    E - RC1-3
    G - RC1-4
    C - L_Tap
    High Side Inverter IGBT:
    E - RC4-2
    G - RC4-1
    C - RC1-1
    Low Side Inverter IGBT:
    E- RC4-12
    G - RC4-11
    C - XFMR2
    ​​​​Snubber S1:
    E - RC4-8
    G - RC4-7
    C - TP between C12 and C13
    Snubber S2:
    E - RC4-6
    G - RC4-5
    C - XFMR2

    Edit - note in my picture that I had the common connection between C12 and C13 the same as XFMR2. This SHOULD NOT be the case - the pair of Snubber IGBTs are in series, emitter to emitter, between these two points. Mine showed a short between the two. The Power Module pre-power checks catches this if you have a later model (after LK050198L), but earlier models don't have direct access to that test point, so if you have a problem on PC2 and PM passes all other power checks, you can do a diode test between RC4-6/8 and the C12/C13 point directly on the module (see attached picture, left side middle). With a diode tester: red lead on RC4-6, black on C12/C13 midpoint should be ~0.6V; black lead on RC4-6 and red on C12/C13 midpoint should give open loop.

    Jon
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    Attached Files
    Last edited by jjohn76; 09-23-2019, 01:24 PM.

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  • jjohn76
    replied
    Unfortunately, there turned out to be many more problems with the Dynasty 200. All resistors across the full DC bus voltage (not looking at it now, but they are the orange transistors in pairs or triplets on PC2 are showing signs of too much heat (mostly discolored traces), the two buss capacitors on PC2 seem like they vented a little into the pocket on the top of the cap (is this normal in the attached picture?), and the power module PM1 seems to have let out smoke (crack on two sides, evidence of smoke venting on bottom of PM1 and the heatsink). Strange though, I check the diodes and IGBTs directly on the board (IGBT tester to check IGBT function), and all work, so I don't know what component in there failed. Has anyone ever seen that before? Either way, I am assuming PM1 got hot enough that it will have a short life.
    Attached Files

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  • Aeronca41
    replied
    Good to know. Thanks for sharing it with everyone! Might help someone else in the future.

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