Announcement

Collapse
No announcement yet.

Syncrowave 250 full amperage output KB057067

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • mewanchyna
    replied
    I haven't put my scope on the gate drive signals yet. I checked all voltages from front panel controls and switches. They all check out fine, including the current adjustment potentiometer.

    From the schematic, the feedback voltage from the shunt goes into one op amp and is sent to the control circuitry. It is also sent off to another op amp to drive the accessory current meter. As I do not have a way to load the output, I detached the shunt feedback and replaced the feedback voltage with a variable power supply (floating) to simulate current flow through the shunt. I was hoping that this would trick the circuitry into changing the firing angle of the SCRs. I looked at RMS voltage at the output hoping to see a corresponding change when I changed the feedback voltage. It sat there at 75VAC. However, this was under a no load situation. I reassembled the shunt circuitry and put a stick electrode and tried SMAW at the lowest current setting. It was evident that it was running full output. I am assuming that there is no change is firing of the SCR but maybe I should verify with the scope.

    I imagine that the welder needs current to be flowing before and SCR firing angles are changed, right? It must start full output and regulate the current within the first several microseconds once the shunt voltage spikes up as current starts.
    Next, I am sorting out where the feedback and current setpoint from the panel meet to make the decision on firing the SCRs. I know they get timing signals from the tap from the transformer. There is an op amp that integrates this signal.

    I am at the point of sorting through the schematic to identify the operation of each section. This is long and tedious. Together, I am sure I will get it up and running.

    Leave a comment:


  • tackit
    replied
    Good to hear from you again Aeronca.

    Leave a comment:


  • Aeronca41
    replied
    Assume you are looking at the gate drive signals with a scope? I’m on the road and unfortunately can’t try to help much for several days. Have you tried looking for changes in the input voltage to the op amps as you vary the front panel amps control?

    Leave a comment:


  • sledsports
    replied
    Originally posted by mewanchyna View Post
    No Hall device on this year. Shunt resistor instead. Nevertheless, thanks for responding. I was starting to feel very alone on this group.
    I wish I could help. But you aren't alone. I miss Cruizer

    Leave a comment:


  • mewanchyna
    replied
    No Hall device on this year. Shunt resistor instead. Nevertheless, thanks for responding. I was starting to feel very alone on this group.

    Leave a comment:


  • MMW
    replied
    I am far from an expert but since no one else has chimed in. I think it may be the "Hall device". If you do a search for (hall device) on this forum you will find many threads on full output syncrowaves. Hoping someone with more tech knowledge will come along soon.

    Leave a comment:


  • mewanchyna
    started a topic Syncrowave 250 full amperage output KB057067

    Syncrowave 250 full amperage output KB057067

    I am trying to fix a 1991 Syncrowave 250. It has no amperage control. The welder was working and suddenly, went full output. I am quite competent in electronics and repairs and need a few hints as to the operation of the control board (135254). I am aware of the fact that the PCB common is NOT at chassis ground potential and the associated dangers with this.
    As it is an older welder, it uses the shunt to detect current flow. It has the problem whether it is pedal or panel control of amperage. The output control works as releasing the pedal will stop the output. The usual things check out such as +15 V, - 15, +10V. Panel controls seem to have proper voltages, non symmetrical -15VDC and +6VDC on the AC balance potentiometer. I disconnected the shunt and applied a small voltage to the feedback pins to simulate between 100 - 200 amps (1.3VDC per 100 amps feedback). This would trick the board into thinking it was supplying 100 amps of welding current. By changing the panel control, it should have changed the firing angle of the SCR's thereby reducing the average output voltage. This had no effect. Knowing what systems are working on the control PCB, I need to figure out specifically where the panel setting and feedback control firing of the SCRs. I could probably change out OP amps and the dreaded Tantalum capacitors which are notorious for shorting out but I would rather troubleshoot this and specifically replace the damaged components. Any help would be appreciated.

    PS anyone have a better digital copy of the schematic than what is in the online manual? Quite difficult to make out pin numbers, etc.
Working...
X