Trouble with Invision 354mp

[daveb56]

Hi Everyone
I haven't posted in a while. I'm having trouble with an Invision 354mp I get a HE.L P-4 code on the display which is a malfunctioning thermal circuitry protector located on the right side of the machine.
I would like to repair it myself if I knew what to look for. Any help would be appreciated.

Thanks
Dave

[ccawgc]

Find RC4 and RC5 on the display pcb. Make sure they are plugged in.
Unplug and measure each one at a time. Should read around 33k ohms at 68 degrees.
Do not push meter probes up in to sockets. it will spread them and keep them from working.
You will have to use a very small screw driver to bend them back.
RT1 lives under the interlink power pcb between the IGBTs. RT2 lives on the other side of the welder on the output diode heat sink, next to one of the diodes. Looks like a ring lug with two twisted wires going to it. The thermistor is glued into the barrel of the ring lug. Replacements are the complete assembly with the plug, wires and lug with the thermistor.
RC4&5 should be on the bottom edge of the display pcb with one on the left and one on the right side of the welder. Two wire plug with a twisted pair of wires.
Both sides should measure the same. Its a lot of work, but they can be switched from one side to the other and see if the fault follows one thermistor or if the display pcb has a problem.

[daveb56]

Sorry about the delay in replying. Haven't had time to check till today. Anyway checked RT1 & RT2 had 42 ohms @ 60 degrees. Where do I check next.

Thanks
Dave

[ccawgc]

Both read 42 ohms with Rc 4 and RC5 unplugged? I think this is a lot low for 60 degrees.
I do not think the thermistors will change from 33,000 ohms to 42 ohms in 8 degrees. For testing purposes, you can replace the thermistor with a fixed resistor or a potentiometer.
Set for 33.000 ohms. If the welder then starts working, then you know the thermistors are bad. or you can try and call miller electric. Ask them the range on the thermistors.
Tell the what you measured and that you got a help 4. They will help a little or give you the phone number of the closest Miller repair shop If it gets to complex.