Can someone identify this transformer?

[Titan91]

I have a nonworking Tatung VS14428 13" monitor chassis and found the transformer at T101 to be bad. The part number is T6001AA LTE. I can't find anything anywhere on this transformer on even a cross reference chart. Where can I get a replacement?

[Ken Layton]

Have you contacted the parts department at Tatung USA?

[05SRT4]

Optimus Prime?

[Titan91]

Is it a proprietary part? I can't find even a trace if information on this anywhere.

[MonMotha]

A picture may help.

It sounds like it's probably a pulse transformer of some sort.  These are often used to couple signals from the sync processor onto the horizontal output. On digital monitors, they are also often used to provide feedback from the horiztonal output to the deflection processor.  They're usually custom-designed/wound for the application at hand.  The part number is probably assigned by the manufacturer of either the part or the monitor.  You can often get spares from the monitor manufacturer, assuming they still have any.  A 13" is probably pretty old at this point.

[Titan91]

Ken based on your posts in the thread below you would suggest emailing Tatung support and sending pictures. Using his photo, which you say is the same model of chassis, the transformer I'm talking about is the large yellow one to the right, which appears to supply power to the rest of the chassis. Since this fails every possible resistance test (exhaustively testing every pin pair) then that explains why the monitor is doing absolutely nothing besides engaging the degaussing coil, which is tied directly to the A/C input and posister before it hits the transformer.

http://forum.arcadecontrols.com/index.php?topic=73158.0

[MonMotha]

Looks like a transformer for a SMPS.  Very likely a custom part used only on this monitor (or maybe a few similar models).  You'll probably need to get it from Tatung, if you can get it at all.

[lilshawn]

i would find it VERY unlikely that a transformer such as that to go open on all the windings.

if they fail, they short. (and quite spectacularly as well.)

i would suspect the switching FET and the control chip first.

[Titan91]

I didn't say it was completely open, some points show a short as well but I know there is a shared trace on the primary side anyway so one of those shorts is probably normal. I will post the test results later. I do find it rather odd that every possible pin pair either shows open or shorted, the transformer looks fine so I assume it hasn't gotten hot or anything.

[lilshawn]

the transformer is what is known as a High frequency pulsed DC transformer. It's probably not going to have many traits similar to a regular AC type of transformer as it operates on a very different principal.

Switch mode power supplies are pretty finicky because of the very low switching time requirements to operate properly. The switching,  often in the 1000000 times per second range, is important to maintain... otherwise the flux in the transformer collapses and no power is produced.

unless it's been struck by lightning or been physically damaged, i believe the likelihood of the transformer actually being bad is very remote. The switching MOSFET has an over current protection built into it. if the load spikes up, it shuts down. the system would shut down long before the transformer would be damaged.

check your AC input rectification (to be sure your AC input is being converted to DC properly.)
and check your MOSFET switcher to be sure it's actually switching.

[Titan91]

Where would the switcher MOSFET be in this case? As in what part on the board? And how would I test it? The rectifier would be the next thing I would test anyway.

[ed12]

as per normal
a/c in fuse,recifter's,filter MOSFET or regulator
look at the primary side of the transformer
the black thing 1 of the leads goes to is your MOSFET
unsolder all lead's and chk it for short
as i fiq u do not have a cruve trace to see if it working right
also there will be a small start-up cap 4.7-10 mf in the primary side to chk
if the mosfet is gone
look at the secdonary side to find if there is a dead short
:diode-range: to ground with the output diode's lifted

ed

[Titan91]

If the MOSFET is shorted the fuse would have failed. If the rectifier is shorted the fuse would have failed. So I'm thinking either the MOSFET is open (rare failure), the rectifier is open, or the startup cap is bad. Considering all caps on the monitor are original I bet it's the start-up cap. I won't be able to test again until a week from now.

Which one is the start-up cap? The schematics don't show the values.

http://forum.arcadecontrols.com/index.php?action=dlattach;topic=131084.0;attach=285563

[lilshawn]

actually you are more likely to find MOSFETS test as being good, but fail under use due to the extremely fast switching required. (don't switch off and on fast enough taking too long to reach full on/off state.)

the fuse is actually there to protect against shorted diodes in the rectifier bridge. (due to surges etc) because they are directly on the mains input.

your "startup" is probably c106. It's really a feedback circuit attached to pin 6. it monitors the voltage output of the FET and adjuststs the duty cycle to compensate for low/high voltage situation. but yes, if the cap is bad the voltage doesn't get sensed properly. sometimes in problematic chassis we have upped the uF of the cap (from 100 to 220uF) to help startup problems.

if the MOSFET has failed it often damages the chip too, so it's recommended you change them both. The chips are used in about 90% of SMPS power supplies, you can get a used one out of an old computer power supply or even by cracking open a high current power adapter. I've never actually bought a new chip, I've always just removed them from old power supplies.

[Titan91]

Ok I've removed the switching MOSFET which appears to be a K1507. Is that correct? The only combination of pins (black on center red on right) gives a reading of 533 which seems normal. Shouldn't the other side give a reading too? Every other combination of pins gives an open reading. Judging by the traces the center lead is the drain correct? Also, the rectifier tests fine.

[lilshawn]

http://www.4qdtec.com/mostest.html

[Titan91]

I get a high reading when using the guide and it quickly changes to open as expected. But when I put black ok drain and red on source, I get 395. When I move red to gate, I get nothing. Is this correct? I test MOSFETS all the time and always get an equivalent reading on both sides.

[lilshawn]

that MOSFET has a damper diode built into it, it's going to throw off the readings a bit. as long as it conducts and goes open it's probably fine.

that said, it's possible it tests fine in this fashion but fail under load.

[Titan91]

Just thinking about ordering a new mosfet, chip, and startup cap. Anything else I would need?

[lilshawn]

possibly a HOT maybe some of the larger elecrtolytic capacitors. hard to tell for sure.

[Titan91]

I finally ponied up enough courage to test this thing live. Connected everything up and flipped the chassis board so I could get readings. Getting 120V across the rectifier AC input, and 168V across the DC output (I assume it reads higher due to the 120Hz pulsing). Getting 168V at 2 primary sides of T101, which I mentioned earlier. So I assume the switching circuit is working? Getting nothing at all on the secondary side, tried several combinations of pins. Maybe there is a shorted/open neutral on the secondary side? To be sure it wasn't pulsing too fast for the meter I tested across a cap on the secondary side (C115) and still got nothing.

So yeah, the transformer's bad. I'll have to look into getting a replacement. 

[Titan91]

Just contacted Tatung, the monitor and parts are discontinued. He says he's never heard of a case where that particular transformer has failed, and he's probably right. Still, I want to believe the problem is something else.

Thinking logically, a switching power supply uses pulse width modulation to create the illusion of different voltages, and the output goes to one or more smoothing caps, producing the actual variable voltage. So with 100% duty cycle the voltage would equal what is coming off the rectifier correct? In that case could the switching transistor possibly be locked on, or the timing IC that drives it? Assuming I would get nothing on the secondary side of the transformer unless there is actual pulsing ( < 100% duty cycle) going on.

[lilshawn]

Without an oscilloscope  you can't be sure the FET/primary is being switched properly. like i mentioned, the FET is switched thousands of times a second.
 you won't pick up the fact the FET isn't switching with a simple voltmeter test. I have had a FET that only partially switched or twitter randomly instead of doing a complete off-on-off-on switch. the frequency of switching time is VERY important, you are relying on a tiny collapsing magnetic field to generate your output.

168 seems a little off I suppose it could be okay (every chassis is a little different.). can you measure the dc output on AC? i'd like to confirm there isn't a failed diode creating a weird situation there. a few milivolts would be okay, a few volts would not. (AC ripple in the DC output would show a failed diode) I doubt this is the case though, but it can't hurt to check.

parts can test okay on the bench, but fail when subjected to the voltage/load of the circuit.

a short on the output side of the transformer would cause the primary load to go up and the FET to go into over current protection. An open on the primary side would likely cause the B+ to wind up out of control and trip the over voltage protection/shutdown/xray etc... (depending on the method implemented)
my money is still on an improperly switching FET.

2SK1507 or if you are feeling lucky, an NTE2989. NTE parts are pretty easy to obtain...most parts places have NTE, but my experience with their reliability has been a crap shoot. sometimes they are good, sometimes they blow right away, sometimes a few months down the road.

a new FET could be had for about $2 each shipped. (less than a buck if you wanted 20 of them) electronic parts have a HUGE markup, so don't buy locally if you don't have to. that same part is probably $20 at your parts shop. I buy IC's locally for 10 bucks each but I can order 25 for the same price off eBay. 

[Titan91]

I get 120V AC going into the rectifier and 168V coming off the +/- sides with the meter set to DC mode. Didn't think to try it in AC mode. I'd say the pulsed output fools the meter into thinking the voltage is higher than in actually is. So you would suggest a new MOSFET? Is the first part you mentioned a direct replacement, and the second part a more universal one? You're also implying it's most likely the MOSFET and not the timing chip that drives it, correct?

[lilshawn]

yes, the 2SK# is the exact part # the NTE is a compatible part#.

You're also implying it's most likely the MOSFET and not the timing chip that drives it, correct?

could be either or both. I'd try the FET first, if it's still not operating then I'd change the chip. sometimes the FET will fail and damage the control chip.

the chips can be pulled out of computer power supplies or plug in "AC adapters" . they are pretty universal used in about 80% of SMPS circuits.  if you are trashing adapters for parts, you are going to want a fairly big one. tiny little chargers for cellphones likely use discreet components and a feedback circuit instead of the "power IC".

Ive never actually "bought" a chip, ive always salvaged the chips from blown computer power supplies. there is only a few different types. if it has the same # of legs it will probably work. if you find a different one, post up the number and i'll check that specs on it to see if it will work for sure.

[MonMotha]

Debugging switch-mode supplies without a scope can be pretty aggravating.  One thing that will probably help is the classic light-bulb test.  Isolate the rest of the monitor from the power supply by removing the appropriate components: a schematic helps a lot.  Then hook a ~60W light bulb up to the main B+ output of the supply, which is typically ~130V.  You may need to load a couple other rails suitably, too.  Now poke and prod and play with it until all the lights turn on.  Now you know you've got a working supply and can attempt to power the rest of the monitor.  With luck, it works.  With less luck, it doesn't work but you've got more confidence where the failure's not.  With bad luck some other fault on the monitor re-breaks the power supply, but that's rare.

[lilshawn]

yes, my next suggestion would be to start removing voltages to sections to isolate a bad one.

no output on any of them is leading me to believe the mosfet is stuck on or is not fully switching off. you need that sharp pulse to make the magnetic field work.

[MonMotha]

If the MOSFET really is stuck on, then you'll pretty quickly blow something.  Most likely the input fuse, but if that's been defeated or similar, probably the MOSFET itself, the bridge, or potentially the primary of the transformer (which, note, is not really being used as a typical "transformer" but rather as a bunch of coupled coils).

If it's stuck off, then of course nothing will happen.  Note that, depending on the design of the supply, the converter may give you no real gate drive in this situation even if the driver chip is fine.  Some (most) designs have a bootstrap RC network that will let the driver chip run for a few pulses but then run the driver chip off of an auxiliary winding of the transformer, while some (few) designs just basically use a shunt regulator right off the input to run the chip.  This makes it harder to test, though.  Again, without a scope, debugging these things in any way other than experimentally changing components and isolating and load testing the outputs is a pain.

[Titan91]

Well as I mentioned I'm getting voltage on several primary side pins but nothing at all on the secondary side. That would lead me to think its a mosfet/IC issue considering there is some sort of voltage on the primary. If its not switching, that could explain why I'm not seeing power on the output. The fuse is fine, but it's overrated. It's a 5A fuse in a 2.5A socket. Would that make any difference? Could I use a logic probe to see if the MOSFET is pulsing?

[ed12]

no to the fuse size issuie
no to the logic probe
this is a job for an isolaction transformer and a scope
as the @ pointed out u want a nice sharp pulse driving the fet

>

« on: May 10, 2013, 08:22:20 pm » Insert Quote

Without an oscilloscope  you can't be sure the FET/primary is being switched properly. like i mentioned, the FET is switched thousands of times a second.
 you won't pick up the fact the FET isn't switching with a simple voltmeter test. I have had a FET that only partially switched or twitter randomly instead of doing a complete off-on-off-on switch. the frequency of switching time is VERY important, you are relying on a tiny collapsing magnetic field to generate your output.

168 seems a little off I suppose it could be okay (every chassis is a little different.). can you measure the dc output on AC? i'd like to confirm there isn't a failed diode creating a weird situation there. a few milivolts would be okay, a few volts would not. (AC ripple in the DC output would show a failed diode) I doubt this is the case though, but it can't hurt to check.

parts can test okay on the bench, but fail when subjected to the voltage/load of the circuit.

a short on the output side of the transformer would cause the primary load to go up and the FET to go into over current protection. An open on the primary side would likely cause the B+ to wind up out of control and trip the over voltage protection/shutdown/xray etc... (depending on the method implemented)
my money is still on an improperly switching FET.

2SK1507 or if you are feeling lucky, an NTE2989. NTE parts are pretty easy to obtain...most parts places have NTE, but my experience with their reliability has been a crap shoot. sometimes they are good, sometimes they blow right away, sometimes a few months down the road.

a new FET could be had for about $2 each shipped. (less than a buck if you wanted 20 of them) electronic parts have a HUGE markup, so don't buy locally if you don't have to. that same part is probably $20 at your parts shop. I buy IC's locally for 10 bucks each but I can order 25 for the same price off eBay.   
<

ed

[lilshawn]

the likelihood of OP having a scope is pretty remote, therefore i suggest that you just shotgun the whole power supply section with as much as you care to replace...

replace the FET and switcher chip and check all the diodes on the primary side see where you're at. if still not powering up, do the caps in around the switcher chip.

[ed12]

100% correct
i tend to think in tech terms

@ u can test the ac side up to the dc side of the switcher
just rember a fue rule's
a=isolate
b=isolate
if in doubt refer to a and b
from there
across the main cap should be about 147-170 vdc,that is right across the cap with it
plugged in >isolate<,from there chassic ground to input of fet or the main filter
the big 1 u
should read the same,give or take a volt
if not look at the fet and switching chip
as pointed out

ed

[Titan91]

Thanks guys, I'll swap a few things including caps because they need swapped anyway.

[Titan91]

Just for giggles I pulled apart a couple of old power supplies. Will any of these MOSFETS work?

C3150M2F3
E13009
U3H217/STPS20
U16212/STPR16
C4106/M7C2

[lilshawn]

the 2SC1507 is a 9 amp 600 volt max MOSFET and has a very fast turn on/off time. (165 nanoseconds to on 360 nanoseconds to off)

2SC3150 - only 3 amps... not enough current carrying capability.
MTE13009 - is an NPN transistor not a MOSFET
STPS20 - is a diode rectifier
STPR16 - is a diode rectifier
2SC4106 - only 7 amps... not enough current carrying capability.

ones that may work in this instance:

2SC...
1101
1102
1503

but at the expense of lower voltage maximums. these are 400/450/500 volt i believe. B+ being ~200 volts, i wouldn't go lower than 400 to have a safe overhead...higher is better too (if you could find a 800 or 1000 volt i didn't have any part # for those.)

keep looking and keep them #'s coming you may still find something suitable. I'll look them up and let you know.

[ed12]

kt's
they are used in plasma smp's
can handle 600v with extreme switching time

ed