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Dynasty 350 HF Troubleshooting

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  • Dynasty 350 HF Troubleshooting

    I started a thread requesting a service manual that evolved into troubleshooting. I can't delete that thread, but I'd like to consolidate it into a "troubleshooting" thread. I'll paste the relevant parts into this first post and this way it will have an accurate title.

    Ok... I finally got the machine hooked up. For those of you who requested the usage stats they are - 415 hours and 135308 cycles. The Unit SN is LH500798L
    I completed a factory reset per the owners manual.

    Today I tested both AC and DC and found them to be functional using the Lift Arc method.

    I checked and cleaned the HF points and set them to .010. HF did not work at all no matter the pedal position or AC/DC. What is my next troubleshooting step?
    I appear to be the only one with that info, but it won't help you.

    Only 2 checks to make

    RC1 check for 325VoltsDC bewteen RC1-1 to RC1-3, unit on at idle

    RC2 check for +15 volts DC between RC2-1 to RC2-2 HF off
    Check for 0 volts HF on

    Or 700HZ betwwen RC2-1 and RC2-2 HF on

    If that is there, all is happy and you need a new PC-7 Replacing parts on this board is probably NOT a good thing. as it may dynamite the rest of the machine.
    I was finally home enough time to check the welder as requested. The results are below:

    RC1-1 to RC1-3: 321VDC stable
    RC2-1 to RC2-2: 0 volts pedal up or down
    RC2-1 to RC2-2: Frequency is unstable when pedal is down and reads in the Mhz (most likely induced voltage from RF)

    During testing the HF worked intermittently (for the first time) and gave both a very strong and sharp crackle for the first few minutes and later on it was about half as loud before stopping. DC voltage never showed on the RC2-1 to RC2-2. I wore rubber linesman gloves and welding gloves and wiggled the RC2 and RC1 wires while depressing the pedal to see if I had any loose connections. That did not change my results.

    If anyone knows how to troubleshoot further I appreciate the assist. Is there a component I should check on the PC-6 tracing it back to the RC14-1 and RC14-8 on the PC6 board? What outputs the 15VDC and 700Hz signals?
    Last edited by wumpscut223; 12-03-2013, 11:40 AM.

  • #2
    Replace PC-7


    • #3

      Respectfully... the service manual reads that RC14 on PC 6 pins 1 and 8 are 700Hz HF Drive referenced to each other. Shouldn't I be able to read that even if PC7 is bad?

      Also - I just noticed you are in Edmonton. I worked in Slave Lake for a summer. It was a great time. I really really enjoyed my time in Alberta. I wish I could go back more often.


      • #4
        I had time to open up the welder further. I tested the output of the PC6 card on the pins that go to PC7 with the 15V and the 700Hz drive when the pedal is depressed. There was no output there either. I'm feeling rather confident it is the PC6 board now, but that board is too complicated to repair. I think I will have to replace it in whole.

        Does anyone agree or disagree? I'm not looking forward to spending $700, and I'm especially not looking forward to getting it wrong.


        • #5
          OK, the 700 hz signal is generated from PC7, and TELLS PC-6 that the HF is turned on. So if its not there then PC-7 is NOT generating HF. This ELIMINATES PC-6 as being the problem!

          What your after is voltage on pins RC8-1 & 3 which according to your earlier post is 321 volts. The answer is with PC-7. Just replace the thing and be done with it!
          Last edited by cruizer; 11-08-2013, 07:11 AM.


          • #6

            On your advice I replaced the PC7 board with a brand new genuine miller part and there is still no HF output. The way I read the tech guide is that PC6 (which has all of the control buttons) outputs the 700hz signal to the PC7 then PC7 uses that timing to output HF to the torch - taking direction from the PC6.

            I was able to get a service manual... reading page 103 in the service manual it says the RC2-1 and RC2-2 are "Input" to the board, not output.

            What do you think our next move is?
            Last edited by wumpscut223; 11-16-2013, 12:58 PM.


            • #7
              Well if you have a service manual, you have the preinspection meter tests, best do that.


              • #8
                I completed pages 61 to 79 of the Miller service manual. I tested everything with a properly calibrated Fluke 123 scope meter. All items tested within limits except for D6 on PC5. The tolerance is .20-.90 and I measured a constant .194.

                What would you like done now?


                • #9
                  Ahhh, scope meter? My 123 doesn't have a diode test function, never used it on it anyways. Those readings in the manual are a simple meter diode test beep and between .2 and .9V


                  • #10
                    It is the diode test, but it also gives the voltage drop across the diode. The 123 is a great meter.

                    I didn't find any faults in prechecks. Do you want me to continue with power on checks? What else should we look at? The weld output and function of all of the buttons is great.... just no HF start.


                    • #11
                      If it was here I'd find the problem is 10 minutes. online its a crap shoot. Really it'll be best to take the unit in somewhere for verification.


                      • #12
                        Cruizer - I really appreciate your help and I'm happy to follow instructions from you. I called my closest miller shop and they charge a $140 minimum just to look at it without purchasing any parts, etc. I'm not making money with this welder, it is a hobby welder for me... my budget isn't big and this isn't a tax writeoff.

                        If you any further advice, I'd really appreciate it.


                        • #13
                          Check T3 resistance R12/13


                          • #14
                            R1 - .3ohm
                            R2 - .3ohm
                            R3 - 198ohm
                            R4 - 200ohm
                            R5-10 - Not checked yet
                            R12 - 0.03Ohm Measured between PC7 RC3-1 and RC4-1
                            R13 - 0.02Ohm Measured between electrode and PC6 RC14-7 (nothing unplugged)
                            R14 - 37.87kOhm
                            Last edited by wumpscut223; 11-22-2013, 02:35 PM.


                            • #15