MTX TA92001 power supply questions & fix - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st January 2010, 11:02 AM   #1
pergo is offline pergo  Italy
diyAudio Member
 
pergo's Avatar
 
Join Date: Dec 2008
Default MTX TA92001 power supply questions & fix

hi all,

i have a huge MTX TA92001 with some problems in the power supply.

The oscillator is TL494 (smd) in open collector mode (with pull-up resistor), that drives a pair of darligton MJD127 (smd) with collector to GND, base to tl494 pin 8 (or 12), and emitter to a tiny transformer. from base, to collector there is a 10ohm resistor.

This tiny trafo has 1 primary (it seems push pull with CT to 12v) and 2 secondaries. The primary has the 2 pulses from tl494 open collector, and generates in the secondary, 2 pulses out of phase, for driving gates of mosfet (STW80NF06).
Gate resistor is 10 ohm.

This is not a push pull smps, because mosfet drain are at 12V, and source is floating and goes to toroid. Center tap of toroid primary is at GND. Only one secondary.

What kind of smps is it? half bridge?

next problem.
I tried to fix one part/toroid of smps (i fix thousand of car amps in italy), but:
1- smps stars without remote on
2- idle current is 1,5A, generates +-100V @12Vin, output stage is OK (no shorts). no hot component. output voltage very clean, low ripple.
3- with remote on, the current rise to 1,7A (i think comparators turn on)

then, i tried to elevate Vin to 14,5V, and i saw that +-100V rise (oh..unregulated).
but when i rise 14V, i heard....boooom!
A small route near comparators (lm339) smokes, and broken.
I resoldered it, and i re-turn on the amplifier....but nothing!
TL494 is standby, heat up, its outputs are HIGH. its inputs are set wrong, with +IN at 0v, and -IN at 5V.....obviously doesn't work. tl494 is ok because i put a new one with same results.

i'm going crazy because the pcb is multilayer and some routes appear and disappear

i wanna rebuilt oscillator, with sg3525 (that i know very well, and i use it for several smps projects) in aftermarket board, by me.
i tried to use my "test board" (fully working) based on sg3525+Ir4427, fully unregulated (but there is an option for feedback, with zener+opto).
i removed, for safety, the diode AKA e KAK from original power supply, tl494 and darlington MJD127 to isolate original circuit from new board .
i linked IR4427 outputs, first time to primary of tiny transformer, then directly to the gate of mosfets.

the power supply starts but works bad. Idle current is 1,5A (but now, there's no output mosfet!!).
Gate waveforms are optimal, no ringing, but IR4427 heat up.
Drain stays at 12V (ok)
Sources turn on very bad. With 100kHz, the waveforms is likely a distorted sinewave 6Vpp (mmm..12 : 2 = ??) but no DC voltage.
I reduced oscillator frequency to 30kHz, and is become more square wave, but again 6Vpp.
Test mosfets (working irfz44..they're cheap) heat very much!

A note:
when the power supply started first time, and generates +-100V correctly, gate waveforms are: positive side @10V, gnd (deadtime?), negative side @-10V, AC and DC coupled o-scope. Frequency is about 25kHz..very low.
How could i generate that waveforms with sg3525? i need tiny trafo and open collector mode?


sorry for the long description.
i'm sorry but i can't make photos of first start waveforms (when it works and generates +-100V)..because now, same setting, doesn't work

Thank you everyone!

Last edited by pergo; 31st January 2010 at 11:08 AM.
  Reply With Quote
Old 31st January 2010, 11:19 AM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
I think this would be considered a push-pull supply but the transformer is driven by followers instead of being grounded as they are in most supplies.

This supply is likely regulated but I'm not sure.

Were all of the transistors clamped to the heatsink when it failed?
  Reply With Quote
Old 31st January 2010, 12:27 PM   #3
pergo is offline pergo  Italy
diyAudio Member
 
pergo's Avatar
 
Join Date: Dec 2008
thanks Perry for the reply,

MTX say "semi-unregulated"....mmm

no transistor are failed.
Original STW80NF06 were removed because they're expensive if failed, and i use irfz44 unclamped, one per primary.
at idle, they shoudn't heat if there's a square wave...but it isn't.
they heat because they don't fully turn on i think, and heat up IR4427..normally cold in other designs.

the main problem is driving gate well, i think.
normal waveform, 0-12V given by IR4427 work on classical push-pull (with CT @12V)..but here not.

i paint an example of original gate waveform (other gate is out of phase), when amp turn on and generates +-100V.
is it right?
why negative side??? n-channel mosfet are OFF both Vds=0 or Vds<0
Attached Images
File Type: jpg Immagine.jpg (21.0 KB, 187 views)
  Reply With Quote
Old 31st January 2010, 12:40 PM   #4
pergo is offline pergo  Italy
diyAudio Member
 
pergo's Avatar
 
Join Date: Dec 2008
photos with sg3525+ir4427:


gate (ringing because there are cable in air from my board, to mtx):
http://img693.imageshack.us/img693/9950/dscn0909n.jpg

source:
http://img707.imageshack.us/img707/1791/dscn0907u.jpg

current:
http://img682.imageshack.us/img682/8253/dscn0908d.jpg


timebase is 10us/div, and voltage is 5V/div.

strange source signal, or not?

thanks
  Reply With Quote
Old 31st January 2010, 12:42 PM   #5
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
The following file shows the typical waveforms for this type of power supply. It's a large file so you should expect it to take a while to download.
http://bcae1.com/temp/mtxamp01.swf

The driver transformer produces both positive and negative voltage swing. The sources of the power supply FETs follow that waveform.

In this amp, it's better to have all power transistors clamped to the heatsink. The voltage regulators, in particular, can fail within seconds and do extensive damage when they fail.
  Reply With Quote
Old 31st January 2010, 12:49 PM   #6
pergo is offline pergo  Italy
diyAudio Member
 
pergo's Avatar
 
Join Date: Dec 2008
Perry, you're very very very professional! thank you!

a question,
how is possibile to generate that tl494 waveform? i don't see driver transformer.
it has a dc component of 6V...
  Reply With Quote
Old 31st January 2010, 01:01 PM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
In the photo, the driver transformer is the small transformer behind the fan wires.

The waveform on pins 8 and 11 of the 494 are at 12v. The waveform looks strange because the transformer is driving voltage back to those pins.
Attached Images
File Type: jpg IMG_2517x.jpg (168.5 KB, 178 views)
  Reply With Quote
Old 31st January 2010, 01:12 PM   #8
pergo is offline pergo  Italy
diyAudio Member
 
pergo's Avatar
 
Join Date: Dec 2008
oh yes! perfect!

the center tap of that driver transformer is @12V?


this is the route that smokes the first time.
http://img203.imageshack.us/img203/377/dscn0912.jpg
Regulators are clamped, Diodes removed.
STW80NF06 original.
  Reply With Quote
Old 31st January 2010, 01:19 PM   #9
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Yes. The attached image shows, basically, how the circuit looks.

I don't know precisely what that trace is for. The fault that caused it to burn must have been a temporary one if it hasn't burned again.
Attached Images
File Type: jpg mtxdriver transformer01.jpg (25.8 KB, 171 views)
  Reply With Quote
Old 31st January 2010, 01:27 PM   #10
pergo is offline pergo  Italy
diyAudio Member
 
pergo's Avatar
 
Join Date: Dec 2008
thank you thank you thank you!

last question, then i go fixing
why pwm starts without remote on?

i lost remote route after the connector i don't know where it goes. Do you know which transistor could be damaged?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help me fix my MTX 1000D, no sound, just static hakentt Car Audio 13 30th October 2009 04:33 AM
Amp power supply questions, attributes jol50 Car Audio 2 23rd April 2009 01:50 AM
Help me fix MTX 152 and MTX 500D hakentt Car Audio 94 8th December 2008 06:26 PM
MTX 4160 and DC power supply interaction ECM Car Audio 3 12th October 2007 06:46 PM
grounding & power supply questions timsch75 Chip Amps 2 15th January 2004 05:04 PM


New To Site? Need Help?

All times are GMT. The time now is 05:55 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2