car amplifier repair question....

jesimon · 11th June 2003, 05:30 PM

I am just getting into amplifier repair. I have just recently built the leach amp with great success.

I have a car audio amplifier that will not turn on. The chassis as well as all the collector and the emitter on the output transistor are sitting at + 12 Volts. A working amplifier of the same type has + 30 Volts on the output transistors' collector and the chassis (heatsink) is at ground.

Does anyone have an idea to what the problem is? I can go into more detail.

Jerad

LukasLouw · 11th June 2003, 06:57 PM

What brand and model is it? What PSU controller chip does it use? Probably the TL494.......... You have to check a few voltages around controller chip to see why it's not working.

Post a few more details, and maybe we can figure it out,

Lukas

jesimon · 11th June 2003, 08:22 PM

It is a hifonics centurion. I will look at it and post more details when I get home from work.

Thanks.

Matttcattt · 11th June 2003, 08:40 PM

its still here? not moved to car audio? its been here 3 hours. the mods are slacking (no offense meant, dont ban me

).

pinkmouse · 11th June 2003, 08:55 PM

Quote:

Originally posted by Matttcattt
its still here? not moved to car audio? its been here 3 hours. the mods are slacking (no offense meant, dont ban me ).

Not slacking, just having a very nice meal

But, now you have my attention, I suppose my "god like" powers could use some exercise

thylantyr · 12th June 2003, 12:40 AM

99% of car amplifier problems
are the power transistors mounted
to the heatsinks whether output
stage or power supply. Remove all
those power transistors and use
a DMM measure each transistor "out-of-circuit", find the bad ones.

Diode · 12th June 2003, 04:14 AM

Unless you have a schematic, you'd be best be advised to take out the suspect transistors and then check them on diode check AND ohms check. Check the switching fets, probably IRFZ series, TO-220 packs. If there is a short, the PWM chip will not turn on into a fault situation. It goes into, what we call, burp mode. It will burp out a few pulses and see if all is OK but if not, it shuts down and won't start. It is a protect mode that switchers use.

Good luck,

Chris

jesimon · 12th June 2003, 05:07 AM

Some more information...

The power supply controller is a korean product KIA494P. I found the datasheet after looking for about 2 hours. A replacement part after comparing onsemi's products would be TL494-D if needed in the future.

I didn't get time to hook up the amplifier to a power supply. But I did completely remove the board from the sink. I can see that the board actually connects ground to the sink, but I know I measured 12 Volts on the sink. How would that be possible without blowing the fuse?

Quick question: I must remove each transistor from the board to insure an operating device? I see that I should do this, but am nervous about doing this (although I am very good at desoldering).

Thanks guys for your help. I appreciate it. We go over circuits in class, but never how to find problems in them. Again, I have always wanted to fix an amplifier and hope that I can repair this amp. Thanks again.

Jerad

jesimon · 12th June 2003, 06:06 AM

Removed the Power Mosfets from the board. They are IRFZ44 power mosfets made by Fairchild. Here are the DMM measures for the 6 devices.
1. Vsd = 0.505V
2. Vsd = 0.501V
3. Vsd = 0.502V
4. Vsd = 0.507V
5. Vsd = 0.512V
6. Vsd = 0.510V

1. Rsd = 2.7 M ohms (IR806H)
2. Rsd = 2.69 M ohms (IR806H)
3. Rsd = 2.69 M ohms (IR806H)
4. Rsd = 2.7 M ohms (IR806H)
5. Rsd = 2.7 M ohms (IR806H)
6. Rsd = 1.4 M ohms (IR803C)

Gate to Source & Gate to Drain were all infinite R for all devices.

Does these seem like good values?

thylantyr · 12th June 2003, 07:42 PM

Which amplifier is this?

If those values were "short" then = bad

It's a good chance they are good, but it's also
possible to have an "open" circuit. But I never
found open circuits during car amp repair, they
always shorted when bad.

Go to step two.

Remove output stage power transistors
and test them.

Later........
When you re-install the transistors and mount them
on the heatsink, typically, you need to isolate the
transistor tab from the metal heatsink. After
mounting them, do a last minute ohms check
between tab and heatsink to make sure there
is no contact. There are a few exceptions to this,
some companies many not have insulators due
to some esoteric heatsink design, I think RF
might do this on some amplifiers.

11th June 2003, 05:30 PM	#1
jesimon diyAudio Member Join Date: Jun 2003 Location: Kansas	car amplifier repair question.... I am just getting into amplifier repair. I have just recently built the leach amp with great success. I have a car audio amplifier that will not turn on. The chassis as well as all the collector and the emitter on the output transistor are sitting at + 12 Volts. A working amplifier of the same type has + 30 Volts on the output transistors' collector and the chassis (heatsink) is at ground. Does anyone have an idea to what the problem is? I can go into more detail. Jerad

11th June 2003, 08:40 PM	#4
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	its still here? not moved to car audio? its been here 3 hours. the mods are slacking (no offense meant, dont ban me ). __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

12th June 2003, 04:14 AM	#7
Diode diyAudio Member Join Date: Feb 2003 Location: Oklahoma USA	Unless you have a schematic, you'd be best be advised to take out the suspect transistors and then check them on diode check AND ohms check. Check the switching fets, probably IRFZ series, TO-220 packs. If there is a short, the PWM chip will not turn on into a fault situation. It goes into, what we call, burp mode. It will burp out a few pulses and see if all is OK but if not, it shuts down and won't start. It is a protect mode that switchers use. Good luck, Chris __________________ The best audio is clean audio!

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11th June 2003, 06:57 PM	#2
LukasLouw diyAudio Member Join Date: Sep 2002 Location: Colonia, NJ	What brand and model is it? What PSU controller chip does it use? Probably the TL494.......... You have to check a few voltages around controller chip to see why it's not working. Post a few more details, and maybe we can figure it out, Lukas

11th June 2003, 08:22 PM	#3
jesimon diyAudio Member Join Date: Jun 2003 Location: Kansas	It is a hifonics centurion. I will look at it and post more details when I get home from work. Thanks.

12th June 2003, 12:40 AM	#6
thylantyr diyAudio Member Join Date: Feb 2001 Location: Mars	99% of car amplifier problems are the power transistors mounted to the heatsinks whether output stage or power supply. Remove all those power transistors and use a DMM measure each transistor "out-of-circuit", find the bad ones.

12th June 2003, 05:07 AM	#8
jesimon diyAudio Member Join Date: Jun 2003 Location: Kansas	Some more information... The power supply controller is a korean product KIA494P. I found the datasheet after looking for about 2 hours. A replacement part after comparing onsemi's products would be TL494-D if needed in the future. I didn't get time to hook up the amplifier to a power supply. But I did completely remove the board from the sink. I can see that the board actually connects ground to the sink, but I know I measured 12 Volts on the sink. How would that be possible without blowing the fuse? Quick question: I must remove each transistor from the board to insure an operating device? I see that I should do this, but am nervous about doing this (although I am very good at desoldering). Thanks guys for your help. I appreciate it. We go over circuits in class, but never how to find problems in them. Again, I have always wanted to fix an amplifier and hope that I can repair this amp. Thanks again. Jerad

12th June 2003, 06:06 AM	#9
jesimon diyAudio Member Join Date: Jun 2003 Location: Kansas	Removed the Power Mosfets from the board. They are IRFZ44 power mosfets made by Fairchild. Here are the DMM measures for the 6 devices. 1. Vsd = 0.505V 2. Vsd = 0.501V 3. Vsd = 0.502V 4. Vsd = 0.507V 5. Vsd = 0.512V 6. Vsd = 0.510V 1. Rsd = 2.7 M ohms (IR806H) 2. Rsd = 2.69 M ohms (IR806H) 3. Rsd = 2.69 M ohms (IR806H) 4. Rsd = 2.7 M ohms (IR806H) 5. Rsd = 2.7 M ohms (IR806H) 6. Rsd = 1.4 M ohms (IR803C) Gate to Source & Gate to Drain were all infinite R for all devices. Does these seem like good values?

12th June 2003, 07:42 PM	#10
thylantyr diyAudio Member Join Date: Feb 2001 Location: Mars	Which amplifier is this? If those values were "short" then = bad It's a good chance they are good, but it's also possible to have an "open" circuit. But I never found open circuits during car amp repair, they always shorted when bad. Go to step two. Remove output stage power transistors and test them. Later........ When you re-install the transistors and mount them on the heatsink, typically, you need to isolate the transistor tab from the metal heatsink. After mounting them, do a last minute ohms check between tab and heatsink to make sure there is no contact. There are a few exceptions to this, some companies many not have insulators due to some esoteric heatsink design, I think RF might do this on some amplifiers.

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