collapse

Author Topic: Fender Mustang 1 Transformer Identification Help  (Read 1937 times)

yustech

  • SSGuitar Regular
  • ***
  • Posts: 26
  • Chip Points: 0
    • View Profile
Fender Mustang 1 Transformer Identification Help
« on: September 20, 2016, 11:03:53 AM »

Hello friends,got this sent for repairs.No power.Check there's no secondary coming out from that tiny transformer.Never bought such component before nor have any idea about its type and data.I don't know what those numbers stamp on it means.

Would appreciate any info about it. Thanks.

« Last Edit: September 20, 2016, 01:15:44 PM by yustech »
http://yustech.blogspot.com/
That Tech & Tutor from greater KD

Vitrolin

  • Master SSGuitarist
  • ****
  • Posts: 63
  • Chip Points: 3
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #1 on: September 20, 2016, 05:14:57 PM »
its a switch mode power supply, you could start by checking if the primary switcher is running, ive seen that more than once...

Enzo

  • Legendary
  • ******
  • Posts: 1842
  • Chip Points: 189
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #2 on: September 20, 2016, 07:58:03 PM »
First off, that is a switchmode power supply, or SMPS.  Unless you know what you are doing they are extremely dangerous to work on.  The mains is directly rectified and filtered meaning high voltage at all the current in the world.  And in general, the control circuits, in fact the whole primary side is NOT referenced to ground or chassis, but instead to -170vDC.  You CANNOT ground your scope to that circuit unless you use an isolation transformer.

SMPS run at very high frequencies, like 50kHz or 100kHz or even much higher.  And not remotely a sine wave.  Your meter will never measure whatever it puts out.

It is far more likely that the primary side, the switching side is not running.  There may be a problem on the primary side causing this, OR there may be a short across the secondary somewhere loading it down and it shuts itself off.  They do that.  There are also usually inrush limiters on the mains wiring, and those are higher failure rate items compared to the rest.

Can you post or link the entire schematic so we can see what we are discussing?

g1

  • Legendary
  • ******
  • Posts: 596
  • Chip Points: 69
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #3 on: September 20, 2016, 08:15:33 PM »
  I believe this is the schematic:

yustech

  • SSGuitar Regular
  • ***
  • Posts: 26
  • Chip Points: 0
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #4 on: September 21, 2016, 01:55:19 AM »

Thank you Vitrolin.
Thank you Enzo.You had saved two lives here.Me and my cheap Velleman scope.Almost put my scope and held the board live :)

To be honest this SMPS thing is very new to me.I'm not much of a theory guy.Just trying to fix stuff,replace what's broken,give it back or earn a few dollars and move on to the next repairs if there's any.EE knowledge doesn't stay long in my brain.Haha

Ok here's what I gather.When turned on I took some voltage reading(in red).Hope we could pin narrow down the fault.So far what I could understand about this circuit are both primary and secondary are isolated.The optocoupler has somesort of virtual connection there.Ignore my opinion if they're irrelevant to the subject.

This is the best I could blow up the schemes,cut it and do some photo font.I'm not good with IT stuff either

http://yustech.blogspot.com/
That Tech & Tutor from greater KD

J M Fahey

  • SSGuitar Global Mod
  • Legendary
  • ****
  • Posts: 4141
  • Chip Points: 429
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #5 on: September 21, 2016, 05:12:04 AM »
You´ll have to learn about SMPS, they are popping up all over the place.
FWIW I am starting to study them.

Seen them for many years in PCs, but didn´t care too much, for 2 reasons:
1) they are cheap and easily replaceable, so why bother?
2) they are standardized, so you junk a bad one, buy anothjer which does the same for peanuts, replace it, end of problem.

But you can´t do the same with those in Guitar/Bass amps :(

Chech the NCP1271 controller datasheet, this Mustang supply and the application example are very close, only difference is the secondary, the example is a laptop power brick supplying 19V @ 3 A , so some 60W ; Mustang secondary and diodes supply whatever a TDA7294 or a TDA2050 needs.

Buy an isolation transformer, 220 to 220V in your case, so SMPS supply is no longer "live mains"  and you can scope and measure.


Enzo

  • Legendary
  • ******
  • Posts: 1842
  • Chip Points: 189
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #6 on: September 21, 2016, 06:44:47 PM »
I have a working understanding of them, but honestly it is my skill as a troubleshooter that gets me through them more so than any specific knowledge about them.

Vitrolin

  • Master SSGuitarist
  • ****
  • Posts: 63
  • Chip Points: 3
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #7 on: September 22, 2016, 04:49:31 PM »
Hi could you take those measurements again with reference to GND at U301 pin4,

pin 6 should be around 15VDC (form D315)
pin 5 needs a scope to be measured see enzos and faheys posts
pin eight should be quite high +300VDC, be carefull it can kill you.!!
the optocoupler on pin 2 is a galvanically isolated feedbak from secondary side, this should be low to operate correctly.


yustech

  • SSGuitar Regular
  • ***
  • Posts: 26
  • Chip Points: 0
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #8 on: September 29, 2016, 10:43:15 AM »
Hi could you take those measurements again with reference to GND at U301 pin4,

pin 6 should be around 15VDC (form D315)
pin 5 needs a scope to be measured see enzos and faheys posts
pin eight should be quite high +300VDC, be carefull it can kill you.!!
the optocoupler on pin 2 is a galvanically isolated feedbak from secondary side, this should be low to operate correctly.

Hey Vitrolin thanks for Ref point,I'm got confused as to where I should put my black DMM lead at. Done what you suggested.

U301 with pin 4 as ref.
Pin 6 has some Voltage fluctuation between 7 to 15Vdc
Pin 8 has from 229 to 300Vdc(yes it is dangerous)

I don't have an isolating transformer..I have a dumb question. If I snap off or dienggage the ground/earth leading out from this amp.Will it be safe for my scope to measure pin 5?
http://yustech.blogspot.com/
That Tech & Tutor from greater KD

J M Fahey

  • SSGuitar Global Mod
  • Legendary
  • ****
  • Posts: 4141
  • Chip Points: 429
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #9 on: September 29, 2016, 02:46:30 PM »

pin 5 needs a scope to be measured see enzos and faheys posts
pin eight should be quite high +300VDC, be carefull it can kill you.!!
the optocoupler on pin 2 is a galvanically isolated feedbak from secondary side, this should be low to operate correctly.
Quote
I don't have an isolating transformer..I have a dumb question. If I snap off or dienggage the ground/earth leading out from this amp.Will it be safe for my scope to measure pin 5?
NO, repeat NO.
You NEED an isolation transformer.
I´ll slightly correct or improve vitrolins post: not only "+300V" will kill you, even "ground" or "-300V" will, because the entire primary side is connected to mains, period.
Floating/disconnecting scope ground may protect ... the scope ... but now touching the scope will kill you.

Simple Universal Truth: IF you want to work with "Offline SMPS supplies" (what you have there) , you NEED a mains isolation transformer.
.
.
.
but ... but ... I know a couple (cheap) techs who repair PC supplies (which have same kind of supply mains problems) and do not have such transformers.

True, a few don´t, but they work in a very primitive way, they work with an unplugged supply , just look for shorts in switching transistors (MosFet or bipolars), primary or secondary diodes or filter caps ... on an unplugged and fully discharged supply.
If they suspect the controller/switcher IC they plain replace it. period.
No scope involved (they don´t even *own*  one , nor know how to use it).


A crude system, but works on most PC supplies, which anyway are cheap and if repair is unsuccessful, disposable.

As I mentioned earlier, PC supplies are generic and cheap and worst case you replace them ... now if that means junking a full amplifier the situation changes a lot.

Check PC computer supply repair videos on YT.
« Last Edit: October 23, 2016, 12:27:14 PM by J M Fahey »

Vitrolin

  • Master SSGuitarist
  • ****
  • Posts: 63
  • Chip Points: 3
    • View Profile
Re: Fender Mustang 1 Transformer Identification Help
« Reply #10 on: September 29, 2016, 04:36:11 PM »
Fahey is right in his correction of my last post anything directly connected to mains supply is lethal.

please take voltage meas on alle U301 pins, not pin 5...
pin 6 doesn't seem right check diodes and caps around it.

...you could make yourself an isolation transformer.
if you mains voltage is 230 or 220V you could take a pair of identical transformers with 110 or 115v sec.
make a series connection with the secondaries and you hav an isolated 230V.
use identical transformers with sufficient powerrating, or you could have some "interresting" results when loading, i have done this myself before i got my hands on a real mains isolation trafo.

 

* User Controls

 
 
Welcome, Guest. Please login or register.
Did you miss your activation email?

* Recent Posts

Gallien Krueger 800RB by phatt
[Today at 02:22:45 AM]


Kay 708 amp repair by Jazz P Bass
[August 19, 2019, 08:30:07 PM]


National GA920P Schematic by mwdavis
[August 19, 2019, 06:55:01 PM]


Pearce A3 schematic by epeirce
[August 19, 2019, 10:16:50 AM]


FENDER MONTREUX by jman
[August 17, 2019, 10:19:25 PM]

* Sponsors