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Syncrowave 250 Relay issue

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  • Syncrowave 250 Relay issue

    I recently purchased a new to me syncrowave 250 from Craigslist. The seller assured me that everything worked the last time it was used... Well, not so much. After wiring it in, and turning it on, i noticed a loud buzzing sound. After removing the panels, it appears that CR6 relay is buzzing. I also noticed that the fan starts to spin for a second then stops. I believe this energizes the main transformer from looking at the wiring schematic. I did some searches and found that this does not seem to be a common problem. Before i just start replacing things, i was curious if anyone had seen this before.
    Little disappointed so far... hoping it is not not a major component like the transformer or board and it is just isolated to a bad relay.

    syncrowave 250


  • #2
    Had time to check out things a little more. After reviewing the wiring diagram again, the CR6 relay must also control the fan. i found the thermostat tp3 that sits on top of the diodes. i un-plugged it, and the buzzing from the relay went away and the fan started. I checked the resistance of the tp3 and it is reading about .1 ohms. You can see the thermostat tp3 circled below. Anyone know what the resistance should measure? Is there a technical manual you can buy for this machine?


    • #3
      Looking at the schematic, on cold startup, it appears there should be essentially zero resistance through both tp2 and tp3, which energizes CR6 and keeps the fan off. When the welder heats up, whichever tp gets warm first opens, breaking the circuit, denergizing CR6, and turning on the fan until the machine cools enough for the thermal switch to close again and shut off the fan. It would seem that 0.1 ohms should be OK but maybe that's enough resistance to keep the relay from pulling in tightly and thus the buzz. Try jumpering a wire across the terminals of tp3 and tp2 (don't get zapped!) one at a time and see if the buzzing stops when you bypass one or the other. If it does, replace that thermal switch. Some old relays just buzz because of loosening internal parts but will still function for years if not decades, and you can either just get used to it or replace it. Check to make sure the relay is tightly mounted. AC relays will often buzz if the mounting screws are loose. CR6 appears to only control the fan; no control of feed to the main transformer I can see on the diagram. Hard to see the big pix on my phone.