Unknown Farnell Power Supply Questions

[Hoiler]

hello everyone,

i have a Farnell GS600-048 power supply, im just asking about if any one has a manual for it or something, or if anyone knows of it. It is a ex-bt power supply from a cabinet that was being thrown out and i though it would be a shame to let it be thrown so i asked for it.
It puts out 48V DC, 12.5 A max, around 600w.

I'd love to be able to convert it to output 12V, that would be so useful. i have heard somewhere that it can be done but there was no explanation as to how.

I'm including some photos just in case someone recognizes it.


Thanks a bunch.
Charles

 

[MikeMl]

Do you have a manual or schematic?

 

[Hoiler]

The nearest thing i can find is a couple of pages of specifications for products similar. But that's it. Nothing else at all on the internet at all..

https://www.electro-tech-online.com/custompdfs/2013/04/103602.pdf

the only other thing i know is that i guess it is a switching power supply due to the fact there isn't a great big dirty transformer in the middle of it.

 

[throbscottle]

I'm confused. It looks like a linear supply as suggested by the big caps and huge heatsink, but as Hoiler says, there isn't a honking great transformer in it - there are 4 smaller ones as far as I can see. Wonder if it's a bit of both kinds - a hybrid.

What do the extra terminals down the middle of the front do?
Why is there a mains connection on the front and the back?
What is SK7 for? Looks like a serial i/o
What's the stripy thing visible through the heatsink? Or is it just vents?
Looks to be a mystery object in front of the heatsink down on the main board between the big transistor and the black transformer - any idea what it is?

Any idea when it was made? Looks like 80's construction - is this a reasonable guess?

I'm only asking because this info might help pin things down a bit, maybe help to work out what is what in there, do a bit of reverse engineering of the relevant bit, rather than the whole thing.

 

[Hoiler]

Yeah it is late 80's i guess. the batteries that i have got that were with it are dated 1993 and amazingly they still hold a charge. SK7 and the smaller terminals on the front are connected some way, seeming that this was part of a bigger BT phone system i know it was used to alert the rest of the system if there was a power loss or fault. i will post more photos in a bit. the reason that there is a mains connection on the front and the back is because that power supply, is inside another case, the black one , and i stripped some other bits out. i hope the photos will explain the questions

 

[Hoiler]

 

[Hoiler]

and one of the transistors is a bux98a

 

[Hoiler]

Look what i found!


https://www.electro-tech-online.com/custompdfs/2013/04/GS600.pdf

 

[Hoiler]

And here is one that was sold on ebay a while ago with hints as to how the voltage may be changed

**broken link removed**

 

[throbscottle]

Wondering if you got any further with this.

I'm guessing the voltage programming by external resistor mentioned in the datasheet takes place using the auxiliary board with the big inductor on it, I'm also guessing that the voltage range programmable by this method is the 35-58v in the datasheet.

Rather interesting to note the input frequency range is specified as 45-440Hz

So I'd have a look to see where the wire from the front panel "prog" connection goes to, and try connecting different resistors to it and see what happens...

Looking at the photo's I can see what looks to be a zener on the main board, also a -12v regulator. Hmm, doesn't help. I would guess you have a psu in your psu to power the circuitry, also there is the battery-backup stuff in there.

I am wondering if it is using SCR's to do switch mode. I think that was popular around the time this was made. It looks like it's got some hefty SCR's in it.

Mention is made in the datasheet of protection and auxiliary functions - I'm guessing the vertical board is probably to do with these.

Would you be able to trace out a block diagram to show how the various sections are connected together? It might shed some light on how it operates, which in turn may provide a route to figuring out which board you need to modify, and from there it shouldn't be too hard, though you may still need to trace out a schematic for the section in question. The block diagram needs to give some indication of which physical components are indicated when it comes to big things like transformers and heatsink mounted devices.

I must say, I'm quite envious!

 

[throbscottle]

This is wild speculation, but I think you may be looking at a small linear supply driving a hefty switching supply.

 

[Hoiler]

On the eBay page, i have messaged the seller who has refereed me to another person. i will hopefully be messaging him soon about it. I have taken more photos for you. As you'll see there are a few model numbers on what appeares to be the mainboard, all saying GS600, meaning hopefully that most components are the same between each model.

I guess i should mention that it will not power up without the other board with the choke on it connected to SK7.

PROG is connected to the mainboard by a white wire, then another orange wire comes off that and goes to SK7

i have tried changing the voltage out with the potentiometer, i can only get a range of about 46 - 52V.

some people have said that i should just get some 48V to 12V converters, but that's no fun. Besides i couldn't run them in parallell as i would want the full 600W , and they are expensive.

I have carefully removed one of the boards inside which has the voltage potentiometer on it and photographed it for you to look at - hope it helps out.

I would be clueless as to where to start when it comes down to sketching out a block diagram of this thing - the nearest i could do is lots and lots of photos, sorry about that. I'm reasonably knowledgeable when it comes down to electronics, and ive fixed a few computer PSUs but nothing like this before, im just thinking it could be a fun thing to try and work on.

Oh, and envious of what? the supply? Lol

 

[Hoiler]

 

[throbscottle]

Yes I'm very envious of you having that lovely big psu!

There's nothing I can see that's a real giveaway as far as changing the voltage is concerned (though it is pretty!) - you are going to have to investigate with a multimeter (and if you have one, oscilloscope).

Nothing special (chips-wise) on the small board - looks like it probably is to do with the battery backup and/or auxiliary functions.
Ok I've spent quite a while looking at this now, also a bit of googling. I think you have an SCR psu here, which is how switch-mode worked before mosfets started to be widely used for them. They were popular around the time your psu was built. That is why there are 2 big SCR's in there. I suspect the 2 T03 can transistors are driving a transformer (or maybe a pair of them) which provides the gate voltage to the SCR's - they are rated at quite a high voltage so a transformer makes sense here.

I guess that the big black transformer is the main high frequency power transformer. If you trace the wiring I would hope you find some big beefy rectifiers connected to it which give your output voltage, and the two SCR's connected (perhaps not directly) to the primary. I think the silver transformer is providing power from the mains to the switching circuits via a linear regulator. I think the big blue capacitors are providing smoothed DC to the SCR's. It would be helpful to know what voltage rating they are however to work out if they are connected to mains voltage (again, it would be better if you can trace the actual circuit).

I'm wondering if SK5 down by the board you pulled off can be jumpered, or have something connected across it to change the voltage. Again, wild speculation here.

There should be some kind of error detection circuit which monitors the output. It will compare this to a reference and produce some kind of signal (probably a DC voltage) which changes the frequency(?) (in a modern smp it would be the duty cycle, but this is old so it may be frequency). So I would try to work out what is creating the reference voltage, and change that.

Sorry this is all speculation, nothing definitive, but I hope it's got you a bit nearer. And I completely agree, 48-12v converters are for WUSSES!

I don't think I'm going to be able to offer much more insight based on photos - maybe someone else can. I'll chip in if I think of anything else.

This might be of some help:
https://www.repairfaq.org/sam/smpsfaq.htm
Also, if you put "scr psu schematic" into google you get some stuff that might give you some insights too, especially if you go on images.
This might help: https://www.electronicspoint.com/scr-regulated-power-supply-t27850.html

As an afterthought, those big transistors seem very hefty indeed - adequate to drive the main supply, so it's a fair guess that they are not your gate drivers but perhaps work in tandem with the SCR's somehow....???

 

[tvtech]

Hi Guys

If throbscottle is correct with it being a SCR switching supply than it would be a design similar to the old Sony 191 TV chassis which used GTO's or Gate Turn Off Thyristors in its PSU. These GTO's became obsolete years ago and we had a modification we used to do using BUW11AF transistors from Phillips (they were the only ones that worked and gave you the correct pulses)....anything else used and bang. Start again.

Also transfomers feeding stuff...about the same time and the same design. Very hard to fix..

I will wait on feedback from you Guys....maybe and only maybe then can we try and repair.

BTW, GTO's became so expensive to Manufacture in the Eighties......companies bailed out. Sony used them in the 191. Never seen them since.

Thank God

Regards,
tvtech

 

[Hoiler]

I have some news, i have tracked down the ebay seller in one of the links above, and have been messaging him about the supply. He says " It was me who gave them the info that they can easily be modified to make them variable voltage, still at the full output current", and that "these supplies can be easily modified (using only one external component) to adjust the voltage anywhere from about 5 Volts to 50Volts".

Sounds too good to be true, huh?

I suspect the way he is going to suggest is messing about with the potentiometer in the power supply. Just got to hope he gets back to me.

Also regarding to the fact that something has to be plugged into SK7 for the supply to start up, i hope that's a matter of connecting a few terminals together on that front panel. Let's hope anyway. I have seen photos of the supply without the SK7 output, and the terminal blocks are wired slightly differently. i may attempt this later on today.

this pic shows how one is configured that does not have a SK7 output.


SK5 does not plug into anything at the moment, even with that circuit board attached. Until i find a schematic or something i'm not going to start poking about inside it any time soon. It's not that i don't trust you guys, but just that i don't trust myself to do it properly.

And at the end of this all, if i decide not to seriously mess about with the supply, i think i will probably sell it on ebay. If you're interested give me a shout. After all it does seem to be a nice rugged supply,just because 48V isn't what i want doesn't mean someone else might want it. They seem to sell from 'never used' £250 to about £50. considering the state mine is in considerably less. Enough to cover the postage and a bit on the side for me anyway.

And on a end note there seems to be a company up north (from my essex point of view anyway) called 'Advance Product Services Ltd' formed out of a load of former farnell and advance technicians and engineers. maybe they might have a schematic or something.

 

[Hoiler]

News! i have managed to get it to run without connecting anything to SK7. by connecting all the front panel connections like the ones in the picture above it will work without the board with the choke coil on it. we are getting somewhere hopefully.

 

[throbscottle]

It would certainly be interesting to see what this "one external component" is!

I hope the Advance Product folks are able to help you out - drop them a polite email, let us know how it goes.

On another note, you could treat this as the transformer/rectifier/smoothing (ie, expensive) side of a hefty linear PSU - there are plenty of designs out there for the regulator part.

On a different other note, I'd have thought you'd be tracing out circuit diagrams by now! It takes a lot of time and patience, but can be done.

I know if I'd found one of these I wouldn't flog it. Just a shame I can't afford to buy it from you if you go down that route.

Good luck anyway, whatever you do.

 

[tvtech]

Hi Guys

Never ignore my posts on Technical stuff...I like to share my little bit of knowledge here..

Go your own way if you think you know better...

tvtech

 

[Hoiler]

I'm sorry tvtech but to be honest i am not looking to truly understand how the supply works, just how to modify it. however no mater what i think, it seems that to be able to modify it i'm going to have to understand how it works.

i did drop them a nice email. i hope they get back to me. That is a good idea to incorporate it into a bigger supply. If this ebay user lets me down i'd love to go down that route .

i have tried tracing the supply out, but im not sure that i will get anywhere with it quickly..,