Thunderbolt AC-DC welder

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I have a Miller Thunderbolt for about 10 years now and for the 2nd time I had either 1 or 2 diodes go out on it. Does anyone know if there is a reason for this or is it normal? I am retired and it is just a hobby for me and it's not used as much as if it were in a business. Do these diodes always go out in DC machines?Welder- Miller Thunderbolt AC 225-DC 150 Plasma cutter, Miller Spectrum 300O/P torch- Victor 100
Reply:I bought my ThunderboltAC only from my elderly neighbor, a retired welder.  He bought it new in 1986, and has never had to repair it.  I am using it a lot, and it welds beautifully!  It is AC only, however.At the Lake
Reply:MPKI have an older Thunderbolt AC/DC and other than having to blow it out inside once in a while, and lubricate the fan and shunt blocks, its never needed anything. Oops, forgot having to repair the adjuster handle that got broken by somebody.Matter of fact I want to sell it. (Too many welders anyway)oldebrush
Reply:I have a Miller Thunderbolt 150 DC-225 AC and after the diodes went out the 2nd time I repaired it myself and found out that it had what I would call a factory defect. What it was is that they did not put any of the heat sink grease on the back of the diodes before they put them in, and also they were not very tight. That could have been the problem with mine. I hope that takes care of this. The diodes have all been replaced now.Welder- Miller Thunderbolt AC 225-DC 150 Plasma cutter, Miller Spectrum 300O/P torch- Victor 100
Reply:I'm pretty sure you have found your problem. Thant's my job. I am a Failure Analysis Engineer for a semiconductor manufacturer, and heat is the main cause of early life failures on semiconductor devices. There has to be a good path for heat transfer to the heat sink.MM175Lincoln AC225 Tombstone
Reply:Sirarcalot,   Thank you for your advise and encouragement on the diodes. I sure do hope you're right  on this. It sure makes sense to me. Thanks.Welder- Miller Thunderbolt AC 225-DC 150 Plasma cutter, Miller Spectrum 300O/P torch- Victor 100