Broken transformer on Carlsbro GRX7

[OrganiK]

Hi all, to summarize I cant work out what the windings ratio, or rather what the VAC output of the transformer is.

A cliente came in with this GRX7 that is a mixer/power amp, quite old thing. Said it stooped working so he opened it up, saw a loose wire and connected it to where he though it went, but of course that didn't fix.

So i open it up and found the transformer was not connected up.

The transformer has 2 primary windings, and 1 secondary winding I live in Spain and we have 240VCA so naturally the to primary coils where connected together, but there wasn't continuity on the primary, so i separated then to find it was only one of them that was an open circuit.

So to determine the voltage output on the secondary winding i decided to just hook up the mains to only one of the primary windings with the secondary winding disconnected obviously (coz the voltage should be 2x since im using 240 on a single P. Winding), and then mesure the voltage on the secondary, and half of that should be the right voltage, right?? I know that's a bit of an assumption, but any way.

When i did that it would just blow the fuse, I then put a slightly bigger one but still blows it. so im guessing that primary has had it too. It measures 4 oms with the multi meter

Any help is much appreciated.

Thanks in advance.

[Khron]

Re: Broken transformer on Carlsbro GRX7

What're the odds you got the windings back to front?

Maybe it has one primary and two secondaries (which would make a lot more sense)?

What DCR are you measuring across the single "secondary"?

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

Pretty sure it is this way round, since the wires are much thicker on the single winding side and the DCR is 0.6 on that side.

Good thinking tho, i ques its a single rail power supply

[R_J]

Re: Broken transformer on Carlsbro GRX7

Post some pictures of what we are dealing with, like the transformer and the rest of the mixer, It should be easy to determine if it has a +/- power supply etc.
My guess would be a single primary and dual secondaries or at least a center tapped secondary

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

here are some pictures, were i show both sides of the the transformer, on one side, the one with 2 windings there is a small misterios hole, the board has a 2 terminals, tagged with +V and -V but there is no GND terminal or tag, so I think it is just a single rail and the -V is just the ground.

Thanks for you quick responses

[R_J]

Re: Broken transformer on Carlsbro GRX7

The pictures are closeups but don't show the complete unit, Picture 4 shows 2 fuses, why would they put a fuse in the ground line?
I see part of a large capacitor, is there only one or are there two?

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

The pictures are closeups but don't show the complete unit, Picture 4 shows 2 fuses, why would they put a fuse in the ground line?
I see part of a large capacitor, is there only one or are there two?

you are right, it is a +/- supply, there are 2 big caps and i just found the GND terminal in in between them!

But still one of the windings that is on the side where there is 2 is open circuited.

Also the DCR mesures 0.6 ohms on the single winding side, and 3.6 on the other winding. that makes me think that i have it the right way round. because there the VAC will be lower on the secondary therefor there will be less turns and les DCR. Right?

And despite all of that, when i connected it up and it blew the fuse, there was nothing connected to the other side of the transformer so there should be only a very small current not enough to blow a 8 amp fuse. but some how i got to find out the VAC out put to order a new one.

one clue i have is that them big caps are rated at 80V, but that doesn't really help much dose it

[budm]

Re: Broken transformer on Carlsbro GRX7

There is sticker on the top of the transformer, can we see straight shots of that label?
BTW, I see two wires (Blue and Brown) on one side of the transformer :
https://www.badcaps.net/forum/attach...1&d=1557945236,
https://www.badcaps.net/forum/attach...5&d=1557945236
if they stick with wire color codes then Blue will be neutral and Brown will be Hot (Phase).
On the other side of the transformer I see 4 wires: Brown, brown, orange, orange.
So I do not see 4 wires for the Hot side in your pictures.

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

here are some more photos, so there is a blue and green one on the side with one winding

[redwire]

Re: Broken transformer on Carlsbro GRX7

I would just pick a winding and inject 6VAC and see what you get out, to figure the out turns ratio on all the windings. A scope helps to confirm phasing.

The thinner wiring should be the primary, if it's got a dual 120VAC primary and putting 220V on one of course it would blow the fuse.

[R_J]

Re: Broken transformer on Carlsbro GRX7

Do you have 7 wires on that transformer? can you ohm out the windindings to match the colors? does one winding have 3 wires by chance?
I also see two large capacitors, Usually one is for the positive supply and one is for the negative supply, they will have a common point which is ground. usually the transformer has a center taped secondary where two wires go to the ~ & ~ on the bridge rectifier and the center tap of the winding goes to ground.
But who knows with this German built mixer.

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

Do you have 7 wires on that transformer? can you ohm out the windindings to match the colors? does one winding have 3 wires by chance?
I also see two large capacitors, Usually one is for the positive supply and one is for the negative supply, they will have a common point which is ground. usually the transformer has a center taped secondary where two wires go to the ~ & ~ on the bridge rectifier and the center tap of the winding goes to ground.
But who knows with this German built mixer.

There seems to be no sing of the center tap on the transformer, you're right about there being a ground terminal in between the 2 caps. Maybe the center tap wire has broken off in side, behind one of the other ones... but I can't see anything behind them

Here's a drawing I just done if it helps

the orange ones were connected together when I got it.

[petehall347]

Re: Broken transformer on Carlsbro GRX7

are those caps in parallel ?

[petehall347]

Re: Broken transformer on Carlsbro GRX7

pic 2 post 5 should clear it up .spades go to bridge .

[R_J]

Re: Broken transformer on Carlsbro GRX7

I would guess blue and green are the secondary 43 volts, Brown and pink 240vac with the orange and (yellow/red???) connected together. and now the winding between the pink and orange is open. You could supply 120vac to brown and orange to see if you get 43vac for the secondary

[petehall347]

Re: Broken transformer on Carlsbro GRX7

i would do the 120v also to find secondary voltage and further testing . been there done that .

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

The thinner wiring should be the primary, if it's got a dual 120VAC primary and putting 220V on one of course it would blow the fuse.

Even if there is no load on the secondary? would a single primary winding not have a high impedance when there is no current flowing though the secondary?

[petehall347]

Re: Broken transformer on Carlsbro GRX7

would spike the secondary then blow the fuse most likely .

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

I would guess blue and green are the secondary 43 volts, Brown and pink 240vac with the orange and (yellow/red???) connected together. and now the winding between the pink and orange is open. You could supply 120vac to brown and orange to see if you get 43vac for the secondary

yer that's what i thought, Still i recon you right about there should be a center tap on the secondary tho...

Havent got means of getting 120vac... i might be able to borrow an old building transformer, that should do right?.

Still dont quite understand why it would blow the fuse by putting more volts on it if there isn't any load on the secondary

[OrganiK]

Re: Broken transformer on Carlsbro GRX7

would spike the secondary then blow the fuse most likely .

what from the inrush current? i though that only happend on caps or motors, im really not sure so please correct me if im rong