MTX Audio 600XD

Dr Zeus · 19th April 2011, 03:22 AM

I've got this amp on the bench with blown power fets which doesnt seem to want to power up. I removed all fets to measure signal on the gate pads, but I'm not measuring anything at all before or after the 100 ohm gate resistors.

The power supply fets are 1H12SL (Fairchild) and measure:
Leg 1: 0
Leg 2: 13.7
Leg 3: 0

TL494C:
Pin 1: 0
Pin 2: 4.76
Pin 3: 0.064
Pin 4: 0.828
Pin 5: 1.482
Pin 6: 3.341
Pin 7: 0.004
Pin 8: 12.94
Pin 9: 0
Pin 10: 0
pin 11: 12.94
pin 12: 12.42
Pin 13: 4.95
Pin 14: 4.95
Pin 15: 4.95
pin 16: 0

This amp also suffered from a small explosion due to this coil closest the spearker terminal outs having what looks like a weak solder joint on the bottom of the PCB. Nothing in this area measuring incorrectly with the DVM at this point.

joesch1999 · 03:48 AM

you need to go from pin 11 and twelve they power the fets and figure out what is bad.

Perry Babin · 19th April 2011, 08:12 AM

If this power supply drives its FETs with a transformer, you won't see the same voltages as a normal amp.

Do you see pulses (any kind of pulses) on pins 8 and 11 or is it straight DC?

Dr Zeus · 26th April 2011, 03:21 AM

I do see +20v waveform. 10 volts/div at 5uS: There is a similar waveform at the fet gate resistors.

Dr Zeus · 26th April 2011, 03:23 AM

Interesting thing is, I wasnt getting anything at all at the gates before just now. Let me try putting this amp back together.

Dr Zeus · 28th April 2011, 04:00 AM

What kind of ps fets can I use in this amp It came with Fairchild 1H12SL and I think legs 2&3 are stuck and shorting. What is 1H12SL? When I do a google search I get a link to this thread!

Dr Zeus · 28th April 2011, 04:02 AM

OH Im such a dummy. i guess thats a 75339P. A 55v 75A transistor. I guess I've got IRFZ48N and IRF3205 fets I could use.

Perry Babin · 28th April 2011, 04:06 AM

I've never had to repair one of these but I've used the 3205s in other MTX amps.

Dr Zeus · 28th April 2011, 04:25 AM

Cool. I replaced the surface mount gate resistors with new 68ohm ones and put some IRF3205s in place. The amp powers, but the PS fets get hot after a short time. The amp produced +55 rail voltage. The waveform on the PS Fets is kind of not good at 10v/Div:

Perry Babin · 28th April 2011, 04:32 AM

Does this amp have PZTA56s driving a transformer?

If so, have you checked them?

Are the 10 ohm resistors between the base and emitter within tolerance?

19th April 2011, 03:22 AM	#1
Dr Zeus diyAudio Member Join Date: Oct 2010	MTX Audio 600XD I've got this amp on the bench with blown power fets which doesnt seem to want to power up. I removed all fets to measure signal on the gate pads, but I'm not measuring anything at all before or after the 100 ohm gate resistors. The power supply fets are 1H12SL (Fairchild) and measure: Leg 1: 0 Leg 2: 13.7 Leg 3: 0 TL494C: Pin 1: 0 Pin 2: 4.76 Pin 3: 0.064 Pin 4: 0.828 Pin 5: 1.482 Pin 6: 3.341 Pin 7: 0.004 Pin 8: 12.94 Pin 9: 0 Pin 10: 0 pin 11: 12.94 pin 12: 12.42 Pin 13: 4.95 Pin 14: 4.95 Pin 15: 4.95 pin 16: 0 This amp also suffered from a small explosion due to this coil closest the spearker terminal outs having what looks like a weak solder joint on the bottom of the PCB. Nothing in this area measuring incorrectly with the DVM at this point.

19th April 2011, 03:36 AM	#2
joesch1999 diyAudio Member Join Date: Jan 2011	you need to go from pin 11 and twelve they power the fets and figure out what is bad. Last edited by joesch1999; 19th April 2011 at 03:48 AM.

19th April 2011, 08:12 AM	#3
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If this power supply drives its FETs with a transformer, you won't see the same voltages as a normal amp. Do you see pulses (any kind of pulses) on pins 8 and 11 or is it straight DC? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

28th April 2011, 04:06 AM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	I've never had to repair one of these but I've used the 3205s in other MTX amps. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

28th April 2011, 04:32 AM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Does this amp have PZTA56s driving a transformer? If so, have you checked them? Are the 10 ohm resistors between the base and emitter within tolerance? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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26th April 2011, 03:21 AM	#4
Dr Zeus diyAudio Member Join Date: Oct 2010	I do see +20v waveform. 10 volts/div at 5uS: There is a similar waveform at the fet gate resistors.

26th April 2011, 03:23 AM	#5
Dr Zeus diyAudio Member Join Date: Oct 2010	Interesting thing is, I wasnt getting anything at all at the gates before just now. Let me try putting this amp back together.

28th April 2011, 04:00 AM	#6
Dr Zeus diyAudio Member Join Date: Oct 2010	What kind of ps fets can I use in this amp It came with Fairchild 1H12SL and I think legs 2&3 are stuck and shorting. What is 1H12SL? When I do a google search I get a link to this thread!

28th April 2011, 04:02 AM	#7
Dr Zeus diyAudio Member Join Date: Oct 2010	OH Im such a dummy. i guess thats a 75339P. A 55v 75A transistor. I guess I've got IRFZ48N and IRF3205 fets I could use.

28th April 2011, 04:25 AM	#9
Dr Zeus diyAudio Member Join Date: Oct 2010	Cool. I replaced the surface mount gate resistors with new 68ohm ones and put some IRF3205s in place. The amp powers, but the PS fets get hot after a short time. The amp produced +55 rail voltage. The waveform on the PS Fets is kind of not good at 10v/Div:

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