Dodgy Repair found in HP6012A Power Supply

[Jay_Diddy_B]

Hi group,

I have to share this with the group. This is the weirdest thing I have seen in 40 years of messing with electronics.

This is a picture of one of the main switching transistors, MOSFET, in a HP6012A 1kW 50V 60A Power supply.




The transistor has been cut open, probably inspected, then carefully soldered shut !!!

Regards,

Jay_Diddy_B

[bitseeker]

 

I wonder what's inside.

[VK5RC]

That is weird!  I am fascinated as to why you would do that.

[Jay_Diddy_B]

Hi,

That MOSFET is still works. I put it on my Tek 571 Curve tracer:



It is the same as another one.

Regards,

Jay_Diddy_B

[128er]

Maybe someone cut it open and hacked a comparable MOSFET inside it? Maybe a TO-220 or DPAK? Why someone should do that? No idea.

Edit: Or someone repaired a bondwire inside?

[jeroen79]

I wonder what's inside.

Only way to know is to open it again.

[bitseeker]

Maybe someone cut it open and hacked a comparable MOSFET inside it? Maybe a TO-220 or DPAK? Why someone should do that? No idea.

I was thinking the same. Although, if they were doing so to try to preserve the look of the original, they should've at least filed down the solder blobs.

Edit: Or someone repaired a bondwire inside?

That sounds plausible.

[bitseeker]

I wonder what's inside.

Only way to know is to open it again.

OK, Jay, time for a transistor teardown?

[tautech]

Maybe someone cut it open and hacked a comparable MOSFET inside it? Maybe a TO-220 or DPAK? Why someone should do that? No idea.

My guess is this ^^^^

[lowimpedance]

Maybe someone cut it open and hacked a comparable MOSFET inside it? Maybe a TO-220 or DPAK? Why someone should do that? No idea.

Edit: Or someone repaired a bondwire inside?

My first reaction to the pic was of course  , but hacking in a comparable device sounded the most plausible to preserve the 'footprint'.
As for bond wires how do you re-attach those without the right gear ??.

I wonder what's inside.

Only way to know is to open it again.

OK, Jay, time for a transistor teardown?

Now everyone is waiting to see whats under the 'hat' !.

[Jay_Diddy_B]

Hi group,

I am reluctant to unsolder the lid. Electrically it is the same as unopened transistor.
It is the craziest thing I have seen repairing stuff.

I believe that the transistor is equivalent to an IRF450.

Regards,

Jay_Diddy_B

[bitseeker]

The primary reason for opening it is to determine what's been done and what impact that may have on the operation of the power supply. How much power is that one switching?

[VK5RC]

Why bother to repair something that hard a way! Unfortunately whilst I would love to see what is inside, IF it is working properly (worth a bit of testing and thermal check out) I would leave it alone myself! (Lazy bugger I am)

[voltz]

Hmm, my advice, replace the part anyway with a new one (if available).. Then open the thing and see whats inside.
If you dont, then who knows how it could fail in the future... Do a proper job, this obviously isn't.

[Gyro]

I very much doubt that you would manage to squeeze much of a package under that lid, certainly not something the size of an IRF[edit:P]450 (unless you sawed that down too!  ).

My bet would be inspection (but why not remove it and test it?) or more likely bond wire. Certainly a desperate step anyway.

The soldering looks a bit blobby so I doubt if there's a hermetic seal at the moment. That could further affect reliability.

[Blastcap]

Come on, we wanna see!
 

[TerraHertz]

That's where they hid the jewels.
Or a small treasure map?

Come on, open it up. And this time when you re-close it afterwards, put in a zipper. 
How much do those cost anyway?

[wraper]

Strongly advise to replace the part as it is not hermetic anymore and you cannot trust it.

[MagicSmoker]

FWIW, the TO-3P package is mechanically compatible with the old TO-3 (now TO-204AA) package. Fairchild FQA13N50CF should be functionally compatible.

The date code on that part says it was made in the 22nd week of 1984, so it's obviously lasted quite a while, but I would replace it anyway. Besides, how can you resist peeking inside to see what - if anything - was done?!?

[Jay_Diddy_B]

Hi group,

The part has been replaced with a metal can IRF450.



I have been saving these parts for 30 years !!

I believe that this was state of the art when the HP6012A was introduced.

The HP6012A is covered in this issue of the HP Journal:

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-08.pdf

Regards,

Jay_Diddy_B

[Tomorokoshi]

It's simply an extreme version of "Don't turn it on, take it apart!"

[bitseeker]

Thanks for the journal link, Jay. I thought that model sounded familiar. I almost bought one locally when I saw it on Craigslist. Of course, since I didn't jump on it, it was gone the next time I looked.

30-year stash of transistors, eh? Nice.

[Kjelt]

The part has been replaced with a metal can IRF450. 

Great  when is the grand opening of the compromised device in the opening post?
That is going to be the best suspense tv/youtube video since the 1986 unlocking of Al Capones Vault by Geraldo Rivera 

[Jay_Diddy_B]

Hi group,

I might open it to celebrate the first shipment of the Batteriser Batteroo...

In the meantime, I put the part on my Tektronix 476 Curve tracer:



The curve tracer indicates an RDSon of 0.32 Ohms at 1A

Here is a picture of a IR IRF450 under the same conditions:



It gives identical readings confirming my suspicion that the 1855-0473 is or is equivalent to the IRF450.

Regards,

Jay_Diddy_B

[setq]

This looks like the sort of repair my father would have done. TO3 corroded? File off the rusty bits and fill the holes with solder!