Snap start hi freq board melted resistor

[Cook county cummins]

My buddy picked up a maxstar 152 with a snap start on the bottom of it but once we plugged a pedal into it no hf. So i took it apart to check the points and found R1 resistor is burnt along with a good size area of the silastic resin and possibly a few other components, but R1 is for sure gone can only see one of the color bands. So was hoping someone here may be able to come up with the original value of R1 and then i can go from there. It currently measures 430 ohms ill get pics up in a few mins . also my first post, been reading for years but always found the answer to any of my welding needs, but this one i have got nowhere on. I have even talked to otc in japan about it but they want to sell me a $578 board, he only paid $400 for the machine and the snapstart together. Thanks in advance

[Cook county cummins]

[Cook county cummins]

Both the snap start and snap start II manuals dont break down the hi freq board. I also have the newest part # for the board if thats helpful to anyone who may be able to help. The otc par # is P10474L00 just trying to get him going on his welder. Lift arc works great though so if its a loss then he still has a great little welder just no hf.

[Bushytails]

The resistor and... something? to the left of the to220 component look like they got pretty warm too, which makes me think the to220 part should be closely investigated as well, and the big diode there. Sorry, can't help with the value of the components.

[Cook county cummins]

Yes in all it looksblike the heat effected area is more than a few components but i figured if i get the r1 replaced with proper value resistor then i could test the rest or maybe it will just work after r1 is replaced

[Cook county cummins]

Any of the miller techs have a guess of what the value could be, should i start high and see what happens i mean its already smoked so i only have a chance of making it work again and since otc will not give me any info i may as well start clipping resistors into the circuit and see what works

[jjohn76]

I think you're best off pulling the board and posting some pictures of the front and back, whole view of the board and sections of the burnt area. We're probably looking at the primary side of the HV transformer and the pulse circuit, but just need to understand the connectors around the area and board layout. What is the output voltage of the step down transformer?

[Cook county cummins]

[jjohn76]

Just looking through the manuals, that looks more like the original snap start than the snap start ii. I have an older Hobart Porta-Tig waiting for a rebuild that looks like it has a similar arc start configuration, will confirm tomorrow.

[Cook county cummins]

Theres a pic of the whole board i had saved on my phone , ill get better pics tomorrow, theres 2 connectors on the right hand side of that pic. One 4pin connector and one 2pin, pic earlier in this thread shows it still in the unit with the connectors connected

[Cook county cummins]

Yes this is out of a snap start, not a snap start II, but in the manual it does not break down the hi freq board, but if someone has one and could measure the value of the r1 that would be a great help john.

[jjohn76]

Here's a bad pic of the arc starter on an older Hobart (Panasonic) Tig welder. Pretty close. Only thing mine is driven off a 200V input voltage, and yours may be different. I'll dig the machine out tomorrow.

[jjohn76]

Correction on both. If your buddy does have a snap start, then it looks like the input voltage to that board is 115VAC on CN 1. My board is 100VAC input. We can confirm values for other components tomorrow. I think you will need to replace a bit of the input circuit. Track down the rectifier - it's either the diode or a bridge rectifier on the board - follow the traces from CN1.

[jjohn76]

Yes this is out of a snap start, not a snap start II, but in the manual it does not break down the hi freq board, but if someone has one and could measure the value of the r1 that would be a great help john.

As promised, here are a couple pictures of the HF board out of an older Hobart Porta-Tig, which looks very similar to your board. I would recommend you check a lot of things before replacing that resistor.



My board also uses a 20W 150 ohm resistor off the board, which is the current limiter through the primary of the flyback transformer. Also on the board, I have a 3.3k 1/2W resistor (R2), 330 ohm 1-3W (probably closer to 2W), the diode (visible in your photos), the rectifier (rectangular block on yours, butted up again the blue MOVs), and a TVS diode connected between the SCR gate and R2. The TO-220 package on mine is an SCR, likely the same on yours judging by the similarity in the drive circuits. It's worth checking diode drop for the rectifier, body diode, TVS, and SCR.

[jjohn76]

Here's the circuit for the HF board, hopefully it gets you sorted so you can start checking components. The big capacitor, C2, charges at the rate allowed by the 150 ohm, 20W resistor off board. Once it charges to the point where the voltage across R4 (R2 and R4 make a voltage divider, giving about 5V across the SCR gate if the C2 capacitor was allowed to fully charge) is enough to trigger the SCR (2V for my SCR based on it's datasheet, so the capacitor C2 only charges to 68V before it's discharged), it discharges C2 through the flyback transformer primary. It discharges alot more current than is sent through the 150ohm resistor, so the C2 voltage drops all the way and below 0V, which turns off the SCR and free wheels current through D3 until all power is transferred to the secondary side. The R3 330 ohm resistor and TVS D2 are there to absorb voltage spikes.


Your board looks like it has all of these components. I don't know what the black cylinder is on what looks like the secondary side. It could be there to limit current through the arc. I recommend trying to get a schematic for your board that looks similar to this, which should help you figure out roughly what resistances are needed. As you're measuring that burnt resistor at 430 ohms, you could be measuring another resistor and shorted transistor (scr, diode, and/or TVS), so it's worth checking each for function as well.

Hope this helps,
Jon