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[Daniel Levi]

There's the question of what the actual working stuff is, though - the board is PSU and control, but there's a heating element?  What exactly does this "T-shirt press" do?

I think that it is just a heated plate/plates that attach the transfer to the t-shirt (similar to a iron press), the electronics will be for temperature control and possibly feature a timer.

[Stephen Swaffer]

I would agree with that analysis-my wife has a couple of these.  Typically just line voltage to the heater elements-honestly can't remember if they are on/off temp control or scr/triac.

Clarify "transformer input"?  THat depends on your point of reference.  I would expect the center tapped primary (voltage into the transformer) to be line voltage-maybe switched to allow use on 120 or 240 volt supplies.

Transformers are pretty robust-especially of they are only supplying power to a solid state logic circuit (ultimately what this board is).  Unless a voltage spike/lightning strike took out the primary, I would be surprised to see both windings open and IF indeed all windings are open what took out the transformer?

It should be fairly easy to follow the power wiring to the input (primary) leads of the transformer.  It could be a bit trickier to SAFELY verify that that line voltage is being applied across the primary leads?  I would only try this while plugged into a known good GFCI receptacle.

I would carefully fuse any replacement transformer to make sure the new one doesn't immediately let the smoke out due to the root cause failure.

[David Allred]

I would agree with that analysis-my wife has a couple of these.  Typically just line voltage to the heater elements-honestly can't remember if they are on/off temp control or scr/triac. There is a triac (BTA16-600B) on the board.  If yours happened to look like this one would you consider opening it up and measuring the secondary voltages?  The controller seems to be common on a lot of these Chinese units.

Clarify "transformer input"?  THat depends on your point of reference.  I would expect the center tapped primary (voltage into the transformer) to be line voltage-maybe switched to allow use on 120 or 240 volt supplies.The transformer only uses the 110 primary leads.  The red (3rd) wire is not connected to anything.  If I referenced input, it would be input to the board, from the transformer secondary,

Transformers are pretty robust-especially of they are only supplying power to a solid state logic circuit (ultimately what this board is).  Unless a voltage spike/lightning strike took out the primary, I would be surprised to see both windings open and IF indeed all windings are open what took out the transformer? No info.

It should be fairly easy to follow the power wiring to the input (primary) leads of the transformer.  It could be a bit trickier to SAFELY verify that that line voltage is being applied across the primary leads?  I would only try this while plugged into a known good GFCI receptacle.Done.  Nothing from secondaries.

I would carefully fuse any replacement transformer to make sure the new one doesn't immediately let the smoke out due to the root cause failure.  Good idea.

Here is another pic that might help.  Except the unit shown is marked 220.  This one owned is not.

[Josh Millward]

I understand that there is no voltage on the output from the transformer when measured across the yellow and yellow/blk wires. Is there any measurable voltage from the yellow and black or from the yellow/blk and black wires?

Also, can you measure the DC resistance of the primary side and also all permutations of the secondary side?

My thought is that if only one side of the output is open, then maybe you can actually measure the other side and find out what the output from the transformer is supposed to be.

So the things you need to measure are:

With AC power connected to the transformer (be careful about not letting leads touch each other!)
ACV Secondary Yellow to Yellow/Blk:
ACV Secondary Yellow to Black:
ACV Secondary Yellow/Blk to Black:

With no power connected to the transformer
DCR Primary:
DCR Secondary Yellow to Yellow/Blk:
DCR Secondary Yellow to Black:
DCR Secondary Yellow/Blk to Black:

I am assuming that the transformer being used has a center tapped output, but the center tap is not being used.

I am thinking that the transformer actually looks like a Radio Shack model that I had used once with a 120V Primary and a 12-0-12 secondary. That would give you 24V on the output side, assuming you are using the two 12V leads and not the center tap. But, it could be anything, so you really need to check and see if there is any useful information that could be retrieved from the bad transformer.

Also, It sort of appears, from what others have mentioned, that it may be possible to operate this circuit from a lower voltage, so it might be interesting to see if hooking up 12V from the secondary side would allow it to work? It may be a temporary fix while you get in a replacement transformer.

[Nathan Riddle]

Last resort is count the windings on the secondary

[David Allred]

To be clear,  the transformer has 3 wires on the primary side.  Black & Blue are used (presumed for 110v from wall).
The red wire is wrapped and not used (presumed for 220v).

There are 3 wires on the secondary side.  Yellow - Black - Yellow.
All are attached to the control board.  Each yellow goes down narrow paths to different areas of the board.  The black goes to a large path ( common / neutral?).

The 2 yellow are identical in appearance.  There is no yellow/black.
Are you suggesting I use the black wire on the primary side to measure with the yellows?

If not, then the readings below are as shown.

With AC power connected to the transformer (be careful about not letting leads touch each other!)
ACV Secondary Yellow to Yellow/Blk:  DEAD
ACV Secondary Yellow to Black: DEAD
ACV Secondary Yellow/Blk to Black: DEAD

With no power connected to the transformer
DCR Primary:
DCR Secondary Yellow to Yellow/Blk:  OPEN
DCR Secondary Yellow to Black: OPEN
DCR Secondary Yellow/Blk to Black: OPEN

[David Allred]

Last resort is count the windings on the secondary

I know that is "mostly" a joke, but are we talking 10's, 100's, or 1000's of windings.  And let me guess, then.... it depends.

[Nathan Riddle]

I know that is "mostly" a joke, but are we talking 10's, 100's, or 1000's of windings.  And let me guess, then.... it depends.

Um, yeah; depends on primary, I haven't taken many apart myself. But I'd sort of assume in the 100 range for the primary and 1000ish for the secondary?

http://www.learnabout-electronics.org/ac_theory/transformers01.php

[Daniel Levi]

Right, the middle/black wire going to the a fat track looks as though it's part of the ground plane which would seem weird as you would expect that to be connected to 0V after the rectifier and that black wire would be for providing 2 separate supplies from the transformer generally for providing a +V and a -V supply which this doesn't seem to need. Although there are 2 capacitors at the top of the board that see to be connecting 2 ground planes so there could be some capacitive coupling going on.

As said before the resistor/capacitor/diode combo at the top left of the board next to the 7805 regulator must be for another supply voltage which appears to be going to the 8 pin chip in the heater control section (bottom of the board, comes from one of the legs of the power resistor at the top left of the board).

[Daniel Levi]

I've done so annotating to the top side of the board as to where I think the power is going and if I get the chance I will do the bottom as well.
The capacitors are a guess as they both seem to be tied to the 0V rail and there is +V from the bridge rectifier going to the first cap.

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