need help identifing diode

Thread Starter

cocobolo95

Joined Mar 10, 2016
21
I have a broken Hypertherm max 20 from 1994. I have determined the problem lies in the chopper board assembly which is no longer available. So I must rebuild the one I have. Most of the components are available. But these 2 large diodes I can find no info on them.

Not having a schematic that shows the chopper, I don't know what kind of diodes these are or their function. The 2 diodes are the same, a TO-3 case with either 2 common anodes or 2 common cathodes. Made by I R markings 1RF350
8P3M
9343G
Can anyone help me with the ID of these diodes. Data sheet would be great. Since they are probably obsolete, a similar replacement diode if you know of one. And is it a common anode or cathode. Thanks in advance for reading and hopefully helping.

Have a pic of the diode with markings.
 

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Thread Starter

cocobolo95

Joined Mar 10, 2016
21
Thanks for the quick reply. Do you know if the 1RF350 is still available. And from whom.

Being new here, how do I get to the user CP to edit my details.

Also, would anybody happen to have a complete schematic for the Hypertherm max 20 plasma cutter. And a service manual would help.
 

MaxHeadRoom

Joined Jul 18, 2013
20,911
I know Digikey stock them, but I am not sure about the old T204 case style, as a last resort you could get the T220 and heat sink it.
Max.
 

Thread Starter

cocobolo95

Joined Mar 10, 2016
21
Heat sinking is no problem. The max 20 has a massive heat sink for the 1RF350's to sit on.

Thanks for the ebay results. Will definitely buy the originals and not the Chinese made ones. I hear horror stories about plasma cutters using the Chinese made MOSFET.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,911
Appears to just show the chopper as a square block.
Probably a PWM circuit, might be possible to just reverse engineer it if not much to it?
Max.
 

Thread Starter

cocobolo95

Joined Mar 10, 2016
21
Reverse engineering is beyond my pay grade. But the chopper board is made up of common components that are easily sourced. Now that I know that 1RF350 is a MOSFET and sources have been provided to me, I can rebuild the chopper.

It would have been nice to have the complete schematic so I could study the working of the circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
20,911
Not sure if you found it, but I came across this.

To Test the chopper you must first find and test the soft start resistor on the rear panel. If it is blown You will have to replace both the resistor and the relay that bypasses it. (3CR). cooling fan must run. Next find the small relay in a plastic box and see if it moves with and trigger pull. The large one with the magnet should pull in also.
The small one turns the chopper on. The large one applies power to the torch. Gas valve should open just after both relays close. We have to have power in the torch before the gas is turned on in order to make a spark and get the plasma working. Look the pc board over real close. looking for any thing burnt. The pc board is part of the chopper assembly and is not available separately. The large capacitor should have around 244 vdc on it.
Other than damaged torches. The common problems are the soft start resistor and relay. Also the chopper on relay waring out. appears to move but does not make contact.
Hypertherm has just announced that these plasma's are at end of life. Which means they are no longer going to stock parts for them. May be available by special order, if it is still made.

Max.
 

Thread Starter

cocobolo95

Joined Mar 10, 2016
21
Thanks for the good info. I have already checked with hypertherm and chopper assembly is no longer available. The 3 relays are still available. It's funny that hypertherm tech didn't know what was on the chopper board or the 2 Mosfet.

Went through troubleshooting with the hypertherm tech. All the relays and soft start resistor checked out as being good. The 4res resistors for piolet arc also tested as good. Which left me with the chopper circuit board and the 2 1RF350 MOSFET on heat sink.

Seeing that unit is 22 years old and has never been repaired, rebuilding the chopper board should get the old girl back up and running again.
 

Thread Starter

cocobolo95

Joined Mar 10, 2016
21
Good point, thought fist symbol was a "1" that's why I thought the semiconductor was a diode. Keep the info coming. I am only a hobbyist who is winging it through the troubleshooting process.
 

MaxHeadRoom

Joined Jul 18, 2013
20,911
Good point, thought fist symbol was a "1" that's why I thought the semiconductor was a diode. Keep the info coming. I am only a hobbyist who is winging it through the troubleshooting process.
IR, as in International Rectifier, there are at least 3 other manuf of these.
Max.
 

ian field

Joined Oct 27, 2012
6,539
Good point, thought fist symbol was a "1" that's why I thought the semiconductor was a diode. Keep the info coming. I am only a hobbyist who is winging it through the troubleshooting process.
The modern part may well have an "IRFP" prefix.

The original part number isn't impossible to track down, so datasheet specifications can be matched to an equal or better modern part - you don't have to only buy IR parts, but if there's a pair of them, they should be replaced as a pair.
 
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