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Old 23rd Apr 2019, 3:17 pm   #1
linescan87
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Default HP 6024A power supply FET.

Hi, can anyone recommend a replacement fet for this power supply? Its marked 5-486.

Thanks,
John Joe.
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Old 23rd Apr 2019, 3:37 pm   #2
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Default Re: HP 6024A power supply FET.

The full HP part number will be 1855-0486.

There are listings of HP part numbers versus manufacturer's numbers floating around the web.

David
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Old 23rd Apr 2019, 4:19 pm   #3
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Default Re: HP 6024A power supply FET.

This part doesn't appear in any of the references I have.
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Old 23rd Apr 2019, 4:57 pm   #4
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Default Re: HP 6024A power supply FET.

Hi lads, thanks for the replies. I was at this last year and drew a blank on a replacement. Have just rediscovered it while doing some much needed spring cleaning. Wondering should I hold onto it or chuck. Would be a shame to throw it out though cause it would certainly come in handy.

John Joe.
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Old 23rd Apr 2019, 5:10 pm   #5
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Default Re: HP 6024A power supply FET.

There are a few direct replacement numbered parts on eBay. May be worth a punt.

Then there’s the possibility of playing guess the IRF part which mostly involves picking something about right and sticking your fingers in your ears. I had to do that in a tek scope preregulator that exploded. It exploded twice again before I got the right part
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Old 23rd Apr 2019, 7:13 pm   #6
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Default Re: HP 6024A power supply FET.

In the HP 6024A manual, on page 5-21 it appears that if Q1 or Q2 blow up there is a very prescriptive flow-chart of parts to be replaced including offending FET's It is possible both FET's are matched as HP supplied them in a service kit.

Usually in this type of circuit the Gate-Source threshold voltage should be close. I guess at the very least replace Q1 and Q2 with similar type then power up and gradually increase the mains supply with a variac while monitoring circuit.

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Old 23rd Apr 2019, 8:56 pm   #7
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Default Re: HP 6024A power supply FET.

Mr. Bungle, I like the idea of guess the IRF number (sounds like my kind of work, haha!) I'll check out Ebay and see what comes up.

Rich, yes sounds like a good idea to use a variac. Thanks.

Cheers,
John Joe.
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Old 24th Apr 2019, 4:31 pm   #8
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Default Re: HP 6024A power supply FET.

Looking through 1982 International Rectifier Hexfet Databook, there are a few 3A TO3 devices highlighted that could be possible. Some are still available manufactured by Infineon but have suffered from die-shrink curse(TO-204).. not cheap.

I guess with the considerable advances in technology it is almost certain current TO-220 package type could be used.

Rich
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Old 24th Apr 2019, 7:05 pm   #9
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Default Re: HP 6024A power supply FET.

Good find. Don't agree with TO220 though. Not enough for this supply.

Spent a few minutes looking at this. Looking at the specifications and schematics I would replace A4Q1, 2, 3 and 4 (assuming all are populated?). These were apparently fitted with 1855-0473 originally. Someone has reported success with IRF450 as a replacement for that part [1] and it looks about right on spec sheet as it's primary side switching.

Now the pain with this is the IRF450 is really expensive or from hooky suppliers only now. After reading further, old FETs never die. IRF450 is now sold as an IRFP450 in TO-247 package! So options are spend or bodge IRFP450's in. The latter are 2.47 a go from Farnell so I'd probably go there.

Disclaimer: EXPECT FIREWORKS.

Edit: also expect that it may have blown whatever drives the gate if the drain flashed over to gate as well. Last time I had a preregulator go on me, it took the following bits out in one go:

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[1] http://www.simonsdialogs.com/2014/09...supply-repair/
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Old 25th Apr 2019, 11:32 am   #10
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Default Re: HP 6024A power supply FET.

Hi again Lads, lots to think about now. Mr.Bungle, IRFP450 sounds like the way to go.

Thanks again,
John Joe.
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Old 25th Apr 2019, 12:40 pm   #11
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Default Re: HP 6024A power supply FET.

Do you really need 500V rated ones ? If so these mil spec ones are pretty good. I have bought parts from this crowd and not received any fake items, they are certainly cheap enough:

https://www.ebay.co.uk/itm/1pcs-2N67...oAAOSwstxVXGDG

If 400V rating will do, go for these lovely ones from Harris:

https://www.ebay.co.uk/itm/2N6760-HA...cAAOSwx6pYq4y1

I have used a lot of Harris TO-3 fets , always wonderful

These ones also look genuine:

https://www.ebay.co.uk/itm/JANTX-2N6...EAAOSwl9BWLDGA
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Old 25th Apr 2019, 2:28 pm   #12
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Default Re: HP 6024A power supply FET.

I’d assume that 500V would be required. 400V is too close to half wave rectified mains for my liking. Imagine a 250V supply (average here!) and that only gives you 50V for a transient.
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Old 27th Apr 2019, 11:56 am   #13
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Default Re: HP 6024A power supply FET.

Hi lads, I've gone ahead and ordered the cheap fet's Argus suggested. We'll see how I get on, they should be here in a few weeks.

Thanks again for all your input,
John Joe.
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Old 27th Apr 2019, 1:24 pm   #14
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Default Re: HP 6024A power supply FET.

Fingers crossed for you. Don’t forget safety glasses!
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Old 27th Apr 2019, 3:14 pm   #15
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Default Re: HP 6024A power supply FET.

If they don't work I'll probably buy a load of IRFP450 and keep trying until the explosions stop....
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Old 4th Jun 2019, 6:05 pm   #16
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Default Re: HP 6024A power supply FET.

Hi Lads,

Back to this. The Fets Argus suggested arrived last Thursday. As it's a rotten day here I decided to have a go at this. Fets fitted and the two 47r resistors replaced it's working away.

Thanks for all your input,
John Joe.
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Old 4th Jun 2019, 8:06 pm   #17
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Default Re: HP 6024A power supply FET.

Excellent. Nice job!
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