Not always, depends on the application, but there could be some circuit board connection between them, either intentional, or in the case of a mishap, accidental!
Max.

Could one tell by the schematic? Not knowing the design of the transformer, if continuity is possibly intentional?
If this were the case one could extrapolate that issues in the power supply circuit board are not bringing the 165 volts down to 85, the way connection to the board is bringing the 92 volts down to 60 (which I will double check). Is there any possible logic here?

 

The schematic would definitely help, it should show one way or the other the configuration of the TXFR.
Max.

 

OK, here is a schematic ...
If anyone can devine anything vis-a-vis continuity between the 60 and 85 volt winding (WHICH THERE IS), it would be much appreciated!
There is a jpeg here, as I cannot scan or create/edit pdf files.
I have also included a link to the service manual in pdf, if anyone has the time to download and view.
The amp in question is a Sony TAN 8550.

https://drive.google.com/?utm_sourc...=gotodrive&usp=gtd&ltmpl=drive&pli=1#my-drive


Once I have re-soldered all the transformer leads back to the power supply board I will report the voltages again.

I am curious if reattachment brings down voltages in one winding from 92, back down to 60.

 

That shows a continuous secondary winding, with the exception of the low voltage pair.
So in that case there would be continuity between all the rest.
The black centre tap is a common to all the rest of the supplies, the voltages shown are at the DC level, did you confirm theseDC voltages, WRT the black common??
Max.

 

Simple answer is no.
Looking at the ~85 marking on the power supply board (as seen in first picture posted), I took this to mean 85 Vac, with that symbol and AC on all the windings.
So set the old Fluke to AC volts and measured the output of the transformer across each of those paired windings.
Nothing was measured in reference to ground, and no DC was measured either.
I had some very wonky voltages in my power supply board rebuild, and want to make sure that the transformer (and my incident), was not the cause.
Once all the winding leads are back and attached, how do I measure the output voltages of this transformer, to make sure it is healthy?
There is a common black wire coming from the transformer, but I always thot the output of any transformer was always AC before rectifier bridges, etc.

 

All the DC supplies are indicated with reference to the centre tap (BLK), which is also the C.T. for all the secondaries, so initially you should have the identical AC secondary voltages from the black to Red & Yellow as from Black to the Org and Grn.
In the photo of the board I do not see the black, I presume it is connected to some common point?
Max.

 

All the DC supplies are indicated with reference to the centre tap (BLK), which is also the C.T. for all the secondaries, so initially you should have the identical AC secondary voltages from the black to Red & Yellow as from Black to the Org and Grn.
In the photo of the board I do not see the black, I presume it is connected to some common point?
Max.

Thanks ffor sticking with this ... I am on a steap learning curve here!
Yes that black lead comes out to a common center point by the filter caps.
Are you saying remeasure the secondary taps with the leads floated from the power supply board, with the meter set to ACv and measure each coloured tap with reference to the common black CT?
Do I also need to float the black CT lead, or can it stay put?
Thanks again for your patience!

 

The black lead is the common centre point for the secondary windings and the common for the DC supplies, (Google full wave rectifier with centre tap).
The result of the windings is four full wave/C.T. DC supplies.
If you measure AC only from the black to the windings either side of it as I mentioned in #26, the readings should be identical for each side red & yell, Org& Grn.
You should not have to remove these to measure the AC.
These have to conform first.
Max.

 

First of all, hello from Vancouver!

This is my first post ... I just discovered this great site this morning.

I am afraid of the answer to my own question here ...

Working on rebuilding a vintage Sony power amp.

During the process with the unit unplugged a SHIELDED lead from charged filter caps somehow touched a post on the power supply board.
This post contained a lead from one of the transformer's secondary windings, supplying 85VAC.

Huge spark and the accompanying noise. Also post melted a bit at point of contact, as did the metal sleave inside the insulated tip of the filter cap lead.

These were 2 coupled 10000uf caps, so lots of juice.

That winding now delivers 135VAC, rather than 85.

The other two windings of 11 and 60VAC are fine.

I would have thought that such a huge inrush of current would have just fried the windings, and they would be open - instead the output voltage seems to have changed.

Does this make sense?

Or does one particular windings in the circuit need to have a load to measure correctly, while others don't (which does not make sense either).

This transformer is unobtanium.

It is possible to read a higher than expected voltage with the winding off load, the only thing I can think of for a voltage as high as you state, is a punch-through of the insulation to the primary winding - but that should never happen!

Just to be on the safe side - do an insulation check from primary to secondary.

 

That shows a continuous secondary winding, with the exception of the low voltage pair.
So in that case there would be continuity between all the rest.
The black centre tap is a common to all the rest of the supplies, the voltages shown are at the DC level, did you confirm theseDC voltages, WRT the black common??
Max.

OK Max here we go ...

Ground>red 45.1 Vac
Ground>orange 45.2 Vac
Ground>green 66.7Vac
Ground>yellow 66.6 Vac

Measuring red/orange and green/yellow without reference to ground (or center tap) clearly just doubles those reading.

This is with all of these leads floated off the power supply board.

So at least both halves of the two secondary windings match. There is continuity between them, and no continuity between them and the 11 volt secondary winding.

So where do we go from here Obi Won?

With the power supply board now pulled, might it be time to check individual components, especially diodes?

PS: I did the Google search as you suggested, and it made sense to me (at least given my limited high school electronic background).

It's interesting to note that the total measured voltages for each winding when floated is 150 percent and 156 per cent of the voltage printed on the circuit board. Not sure if this is significant or not, but they are at least close to one another.

 

It is possible to read a higher than expected voltage with the winding off load, the only thing I can think of for a voltage as high as you state, is a punch-through of the insulation to the primary winding - but that should never happen!

Just to be on the safe side - do an insulation check from primary to secondary.

Hi Ian,

Is this something one can measure, or does it require one take the transformer apart?

 

The transformer looks OK, Next it is time to measure the 4 individual power supplies, the two +ve and the two -ve voltage WRT the black common.
The rectified DC goes to four regulating transistor circuits, fortunately you have the schematic to work through, purely DC now.
Max.

 

The transformer looks OK, Next it is time to measure the 4 individual power supplies, the two +ve and the two -ve voltage WRT the black common.
The rectified DC goes to four regulating transistor circuits, fortunately you have the schematic to work through, purely DC now.
Max.

Will do Max ...

Are you referring to the + 88v and +60v on either side of C 335 and the -88v and -60v on either side of C336?

This is the first voltage reference I can see on the schematic coming out of the diodes for each of those voltages.

 

You start with the output of the rectifiers and work methodically through from there for each of the four supplies.
Predicted Voltages are shown on the print.
Max.

 

Hi Ian,

Is this something one can measure, or does it require one take the transformer apart?

Normally you'd use a made for the job insulation tester, a PAT tester might be easier to find/borrow.

In the light of the mishap described - either there's a short to the primary, or there isn't.

Any leakage between any separate windings indicated by the high Ohms range of a DMM would be a fault you can't ignore.

 

I never saw any reference to a continuity to the primary?
The fact that the secondary voltages all appear normal seems the TXFR is OK?
I took the OP had not taken voltage readings from the best point and was confused at the result?
The four secondaries are all referenced to a common centre tap, so there obviously was continuity between the windings.
The way I see it so far anyway.
Max.

 

I never saw any reference to a continuity to the primary?
The fact that the secondary voltages all appear normal seems the TXFR is OK?
I took the OP had not taken voltage readings from the best point and was confused at the result?
The four secondaries are all referenced to a common centre tap, so there obviously was continuity between the windings.
The way I see it so far anyway.
Max.

I have not done any continuity tests with reference to the primary winding, as those leads are buried in the amp.

Assuming the transformer is OK, and I read the schematic correctly, the first reference readings on the schematic out of the diodes are at C335 and C336.

At the positive end of C335 the reading should be +60v it's plus 63v
At the negative end of C335 the reading should be +88v it's plus 68v

At the positive end of C336 the reading should be -88v it's -71v
At the negative end of C336 the reading should be -60v it's -57

So the 60v rail (if that's what it's called) is +/- 5% which I assume is acceptable.
The 88 volt rail is off by much more, the positive side is out 23% and 19% on the negative side.

That clearly won't work.

I have tested all the diodes in both paths with a fluke meter on diode mode.

There is no reverse continuity in any of the diodes.

D332 (double diode) voltage drop 0.505/0.484v
D332 (bouble diode) voltage drop 0.511/0.490v

D334 voltage drop 0.539v
D331 voltage drop 0.599v


I am so open for any ideas!!!

 

At the positive end of C335 the reading should be +60v it's plus 63v
At the negative end of C335 the reading should be +88v it's plus 68v

I am so open for any ideas!!!

The print shows the C335 Pos = 88v and C335 Neg 60v, but in any case it may appear that one of the full wave rectifiers is open on that positive side?
If you have a diode checker position on you meter, you may be able to tell if it is open.
Max.

 

The print shows the C335 Pos = 88v and C335 Neg 60v, but in any case it may appear that one of the full wave rectifiers is open on that positive side?
If you have a diode checker position on you meter, you may be able to tell if it is open.
Max.

Hey Max ...
The Fluke does have a diode testing setting ...
I just checked both full wave rectifiers again, voltage drops look normal in forward position (as recorded above), no continuity the other way (when leads are reversed) on either side of each unit. I am not sure what you mean by "open".

 

If only one is conducting this will give a low voltage.
If the rectifiers are OK it is a possibility the Electrolytic is open?
Max.