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Electronics => Repair => Topic started by: deth502 on February 08, 2019, 12:46:46 am

Title: diode replacement.
Post by: deth502 on February 08, 2019, 12:46:46 am
here goes the long story. for the short version, skip to the end....

i have a cheap chinese plasma cuter- a cut50, forget the brnd, that i have been using for a while. 110v machine and it works great on sheet metal, with the dial usually at about 1/3 up. today i had to cut some 5/16" plate and i thought id give it a try to make things easier. fired it up and it only gouged about half way trough. so i turn the amperage dial up to about 3/4 of the way, and have a go at it. it cut for about 1.5-2 sec and a saw a flash from the vents on the front of the machine, and that was that.

i opened it up and saw a resistor that was burnt to a crisp, it still read at 25.23k so i going to take a huge leap of faith and assume this is a 24k resistor. there are also 2- 330k resistors that apparently arced and welded themselves together. i dodnt test them at first, but after i separated them they both still read within spec. these are just like giant 1/4 resistors, i thiknk they are 5w, but they are not ceramic, ive never seen anything like them before. but to get back on track..  before the resistors on the output side (where all the power comes out) there is ...kind of... a set of 4 diodes, only one has been doubled up on. i checked these and several were open. im assuming this is why the resistor caught fire. searching the internet, i found a video of a guy with apparently the EXACT same problem i had. you can see in his video the one doubled up diode i spoke of also. the board layout is a bit different, but...

https://www.youtube.com/watch?v=9A3N7ZcecRM (https://www.youtube.com/watch?v=9A3N7ZcecRM)

so, it would seem this is a common problem. i dont want to do it again. searching the components, the one i removed seems like a very plain jane (other than being rated to 2kv@.2A) diode.

http://www.semicon.sanken-ele.co.jp/sk_content/rp%201h_ds_en.pdf (http://www.semicon.sanken-ele.co.jp/sk_content/rp%201h_ds_en.pdf)

now, i CAN get this diode to replace them, but again, i dont want to come back to this again. so im thinking of throwing in some hvm12 to beef it up

https://www.mouser.com/datasheet/2/345/hvm-1201156.pdf (https://www.mouser.com/datasheet/2/345/hvm-1201156.pdf)


----------------------------------------------------

short story..

so, would a hvm12 be a good replacement for the rp1h in this instance?
Title: Re: diode replacement.
Post by: keymaster on February 08, 2019, 02:40:48 pm

so, would a hvm12 be a good replacement for the rp1h in this instance?

No , rp1h is a Fast Recovery Diode ,hvm12 isn't.
Title: Re: diode replacement.
Post by: deth502 on February 09, 2019, 12:49:11 am
ok, thanks. see, thats why i ask, im no good at dissecting all of the subtleties of a data sheet.

is there any beefier part (that will not break the bank) that is suitable to put in in their place?   
Title: Re: diode replacement.
Post by: keymaster on February 10, 2019, 12:13:38 pm
it is surprising difficult diode to match .
1. GAP3SLT33-214
is faster ,it can handle digger voltages , more current . but is in smd package .You can use the leads from the old diode .
(https://www.mouser.com/ProductDetail/GeneSiC-Semiconductor/GAP3SLT33-214?qs=sGAEpiMZZMtQ8nqTKtFS%2fMVO5fHW5uUQrQbtp%2f9MuOSn8pflXoqULg%3d%3d (https://www.mouser.com/ProductDetail/GeneSiC-Semiconductor/GAP3SLT33-214?qs=sGAEpiMZZMtQ8nqTKtFS%2fMVO5fHW5uUQrQbtp%2f9MuOSn8pflXoqULg%3d%3d))

2.BY203-20STAP
is 3 times slower(worse than the original but still way better than hvm12) it can handle more current and in through Hole package . the cheapest of all .
(https://www.mouser.com/ProductDetail/Vishay-Semiconductors/BY203-20STAP?qs=%2fha2pyFadujR63Y9vK37TLjHex%252bXgi0gaHMaPtzwGlH1gvElXe77Yg%3d%3d (https://www.mouser.com/ProductDetail/Vishay-Semiconductors/BY203-20STAP?qs=%2fha2pyFadujR63Y9vK37TLjHex%252bXgi0gaHMaPtzwGlH1gvElXe77Yg%3d%3d))

3.DH40-18A
same speed ,it can handle a lot more current(with the proper heatsink) but is 1800V (vs 2000V of the original)
(https://www.mouser.com/ProductDetail/IXYS/DH40-18A?qs=sGAEpiMZZMtoHjESLttvkpfqOErzsE88yk8kJN%252bq6B4%3d (https://www.mouser.com/ProductDetail/IXYS/DH40-18A?qs=sGAEpiMZZMtoHjESLttvkpfqOErzsE88yk8kJN%252bq6B4%3d))

I personal would go for the no.1
Title: Re: diode replacement.
Post by: deth502 on February 12, 2019, 09:38:29 pm
thanks! looks like ill be ordering some of #1. being smt i could always build a little breakout board to mount them too. hopefully the bigger specs will have them lasting the long haul (or close to it) over the stock parts that seem a bit puny for the application. the $10-13 seems a bit steep, but a lot better than some of the diodes ive seen searching ($30+!!! wtf?!?)
Title: Re: diode replacement.
Post by: Yansi on February 12, 2019, 09:51:43 pm
Why not to get the RP1H directly?
Title: Re: diode replacement.
Post by: deth502 on February 13, 2019, 01:06:20 am
again, because mine broke, and in searching the net, apparently a lot of other peoples broke. makes me think the part is under spec'ed and im not looking to make this repair a regular thing.
Title: Re: diode replacement.
Post by: Yansi on February 13, 2019, 01:20:56 am
Okay, understood!