Help replacing 4 diodes with rectifier and improving old AT PSU

[keropi]

Hello!

I am trying to recap and improve an old AT PSU that I plan to use with a 386DX pc

Here is a photo of the pcb:



Input caps are Panasonic 330uf/200v so I left them in alone , all other caps were PCE-TUR and missing from the photo for obvious reasons

I will replace the missing caps with Chemi-con ones and I am thinking about replacing the 4 diodes with a rectifier and maybe adding some of the missing input filtering.

The 4 diodes:







How do I solder a replacement rectifier like this?



Is it a good idea? I have a KBL406 rectifier available which is more than enough for a PSU like that AFAIK. But I would really appreciate some help on soldering it and avoid a fire


The missing input filtering:

As you can see they did half a job with the input filtering:



Should I use this filtering PCB with the PSU?



Maybe transplant the common mode choke and X-Cap to the main PSU pcb? What do more knowledgeable people think?


Any help/info will be greatly appreciated ! Thanks in advance!

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

just change all the caps for panasonic FR or FC

the diodes were good enough when it was new - if the board isnt darker under them then they arent heating up.

filters? who needs filters!!

[CapLeaker]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

changing the rectifier diodes on that board? pointless... unless they are bad or there is a heat problem...

[SteveNielsen]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

I still wouldn't replace them with a single-package bridge. Discrete diodes can dissipate heat faster. If there is a heat problem a bridge isn't likely to to help.

[keropi]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

Thank you all so much for the suggestions/help, seems like the diodes will remain in place.
There isn't any problem with them , I just thought a bridge rectifier would be better to have.

What about input filtering? Do you think I should bother installing missing components?

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

no, if the psu caused interferance then the parts would have been fitted originally.

i'v done a number of AT supplies, one just a few days back.
i just do a full recap with pansonic FR & FC and change the fan.

well that and add a power switch inplace of the power outlet.

[keropi]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

allrighty then! I'll do just that with a small change: nippon chemi-con caps instead of panasonic ones: I can't get another quality brand here other than chemicon (tbh I can't complain because the other alternative is LeLon caps....)

thanks again for all the help!

[kaboom]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

no, if the psu caused interferance then the parts would have been fitted originally.

Really?!

I can't see it doing anything besides that...

First, PSes had full input filtering. Then cheapies/fakes took it out, because they were cheap.

Now, you mean to tell me/us that all these (originally) POS power supplies were individually tested, and those specific ones creating RFI/EMI, were pulled from the lot and had filtering added?!

I don't buy that story; in fact, I don't even rent it.


Keropi, I'd transplant the parts from that filter PCB, putting the X-cap at C1...

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

one pcb, mutiple ratings of supply.
the 200w one may have not had filters while the 250w one that pushed the transformer harder would have had them.

[kaboom]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

Are you shittin me!?

The filter was left out for cheepness and you know it. I'll bet that thing also had black/white line/neutral wires, since it looks like one intended to be dumped in the US.


How come after I put a Sony 9W (9v, 1A) SMPS wallwart into a bigger enclosure for someone, and added an actual line filter, conducted RFI was zip ten feet from the supply cord?


Your idea is preposterous. Even the "widdle baby" SMPSes in printers have the filters. I personally know of a Deer that spewed trash all the way up into the FM BCB- 88-108 MHz, let alone HF. You could hear the birdies between strong stations, weak ones were wiped out.

one pcb, mutiple ratings of supply.
the 200w one may have not had filters while the 250w one that pushed the transformer harder would have had them.

Then it would state different values or ampacities for said filter components, not omit them completely, you antecrep double!!! Do you see the filter components marked as optional on that PCB?!

Next, I suppose you'll try to tell us that the Pi-choke, on the output side, is "optional depending on wattage."

Remove the output caps, and enjoy the squarewave; you can't integrate the trapezoid coming from the output inductor without the filter caps!!!!

Get it right or stay home, imposter.

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

Are you shittin me!?

The filter was left out for cheepness and you know it. I'll bet that thing also had black/white line/neutral wires, since it looks like one intended to be dumped in the US.

shows how much you know.
ALL psu's sold in europe up until recently used that colour code even if it aws a $1000 sgi supply or a top-brand pc one.
most still do.

maybe you would prefer black & red, or brown & blue, or just pink for the LGBT assholes.
the wire colours do NOT indicate build quality or intended market.

one other thing, AT supplies oscillate at much lower frequency's - they dont usually have pie filters because such designs wont work well at lower frequency's.

[budm]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

But pi filters have been used in 60 Hz 120Hz power supplies output filters for decades, that is LOW frequency.
Or are you referring to the pi filter at the AC side?

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

i was refering to the outputs, but at lower frequency's the filters need larger cores so unless you want huge coils ( and i do have a couple with them) it's not really viable.
the ones i have with output coils are not AT/ATX form factor, they are huge.

[kaboom]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

But pi filters have been used in 60 Hz 120Hz power supplies output filters for decades, that is LOW frequency.
Or are you referring to the pi filter at the AC side?

I was referring to the O/P side, but even at power-line freq, both pi filters (well regulated supplies, even tube equipment) and common-mode filters are/have been used.

shows how much you know.
ALL psu's sold in europe up until recently used that colour code even if it aws a $1000 sgi supply or a top-brand pc one.
most still do.

What color code? Black/white??? You're kidding.

So all the EU-spec supplies were China-pride Deers and other such junk? Wasn't the standard in GB, for single-phase, red for hot, black for neutral, and green w/yellow stripe for bond/ground/EGC?

Why does this strike such a nerve with you?! How come, before "brown/blue" became standard, did a legit power supply for international markets not use black/white?

I'm surprised that you, of all people, never mentioned this: "duh, let's put black&white wires in our fake export supplies- them dum'mericans will never know the difference." If what you state above is true, then everything in the world is black or white...

maybe you would prefer black & red, or brown & blue,

Black and red, FYI, are both colors for hot in 120/240V, and 208V systems. Brown, that's a hot in a 480/277 system, and blue is third phase for 208. Uh-oh! Brown and blue??? Phase A from a 480 bank to phase C of a 208 bank? NEC violated, call Mike Holt and Joe Tedesco!

the wire colours do NOT indicate build quality or intended market.

I've heard it all before...

one other thing, AT supplies oscillate at much lower frequency's - they dont usually have pie filters because such designs wont work well at lower frequency's.

You can't make such a broad generalization. And for the record, early deer ATX supplies just had the 5VSB board above the main PCB, straddling (and attached to) the heatsinks. Remote on/off was just pulling the deadtime control pin of the 494 to max deadtime for "soft off." IOW, an AT supply by any other name.

Where do you get the idea that the intended load is what determines switching freq? There are constraints based on topology (full/half bridge, forward converter, flyback), transformer/inductor core, wire size, losses in O/P rectifiers and BJTs/MOSFETs. But other than accomodating those limitations, the load in no way "dictates" the switching freq, in computer, or any other SMPS.


With that out of the way, why don't you address the issue of filtering? If I believe your story (which I don't), how come that PCB is marked for those filtering components, rather than having alternate silkscreens for "different capacities?"

i was refering to the outputs, but at lower frequency's the filters need larger cores so unless you want huge coils ( and i do have a couple with them) it's not really viable.
the ones i have with output coils are not AT/ATX form factor, they are huge.

Don't do an SMPS apples and oranges with me, comparing a line-freq supply such as this:


to the pi section at the output of an SMPS, citing "huge inductors" as the reason for leaving them out.

You and I know damn well that those inductors are often replaced with jumpers in deers, etc, for cheepness.

[budm]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

"they dont usually have pie filters because such designs wont work well at lower frequency's."
I was referring to this comment regarding to the pi filter and low frequency, it works just fine when you design it for the frequency you are dealing with.
I grew up and worked with tube equipment for a long time and nothing wrong with pi filter at low frequency.
In the really old day of tube radios and TVs they that choke of the pi filter as part of the speaker that does not use permanent magnet, it uses that choke as electomagnet in place of the permanent magnet.

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

What color code? Black/white??? You're kidding.

So all the EU-spec supplies were China-pride Deers and other such junk? Wasn't the standard in GB, for single-phase, red for hot, black for neutral, and green w/yellow stripe for bond/ground/EGC?

Why does this strike such a nerve with you?! How come, before "brown/blue" became standard, did a legit power supply for international markets not use black/white?

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

Where do you get the idea that the intended load is what determines switching freq? There are constraints based on topology (full/half bridge, forward converter, flyback), transformer/inductor core, wire size, losses in O/P rectifiers and BJTs/MOSFETs. But other than accomodating those limitations, the load in no way "dictates" the switching freq, in computer, or any other SMPS.


With that out of the way, why don't you address the issue of filtering? If I believe your story (which I don't), how come that PCB is marked for those filtering components, rather than having alternate silkscreens for "different capacities?"

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You and I know damn well that those inductors are often replaced with jumpers in deers, etc, for cheepness.

firstly i never related load to frequency, i related AGE to frequency.
old psu's often ran 30-50khz, modern ones run 70-200khz.

second, i'v never even seen a "Deer" other than in a park.
the worst pc psu's i'v had are CodeGen and those go directly to the bin.

i work mostly in industrial equipment and if you think SONY, TDK, Delta etc dont use white & black you need to expand your horizons beyond shitty $10 pc supplies.

[budm]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

http://www.openelectrical.org/wiki/i...le_Colour_Code

[stj]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

that's nice, but it means nothing for internal equipment wiring.

there are other non-standard "standards" too i see a lot.
for example, building wiring.
red for switched live, yellow for unswitched.
very common when i see light fittings with integral battery backup.

[Behemot]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

I would not stick such low-ESR caps as FR/FC into two decades old PSU, but stj does not know anything else than that. Remember than the best at those times were not even Chemi-Con LXZ which were used on motherboards. Many years later the ultra-low ESR caps arrived, those went on MB and the previous best went into PSUs. Who knows what especially FR would do in there.

Chemi-Con KYA and Samxon RS I have are much more suitable for that.

[Stefan Payne]

Re: Help replacing 4 diodes with rectifier and improving old AT PSU

You should replace _ALL_ caps. Not just those on the secondary side. Also the caps between those two heatsinks...

You may only keep the primary caps. Besides them, you should replace anything else.

And as mentioned: you should replace the original caps with something equivalent. So if they used general purpose caps, you also should use general purpose caps...

Do _N O T_ use Low ESR or Low Impedance caps on those units. That might not be a great idea...