Hi
I'm posting to see if anyone would be able to help me out. I have some basic repair knowledge with electronics and have somewhat successfully fixed amplifiers in the past before, but I'm am stuck here. I'll try to describe below what I've checked so far, forgive me for any technical/naming errors ...
This amplifier is a class D, mono output, and when powering on (energize rem line with 12v), the amp acts like one of the output's are shorted on - there is a loud pop and the sub immediately moves to the max travel, reading voltage over the sub is about 38v negative. (referring to the + / - for speaker hook up), and obviously things get hot quick. I initially jumped the gun and assumed the output mosfets were burned and tried replacing all 4, to no such luck.
The amplifier has 2 internal rails, which feed into 2 groups of 2 IRF640's for the final audio output. From what I can tell there looks to be a positive and negative phase.
At idle (no audio signal), I've measured the voltage input to pair of gate inputs on of IRF640 for what I coined the negative phase to be +~28 volts. This one I suspect there is a problem with as the speaker output is also negative when at idle (more below)
At idle, the voltage input at the positive phase gate inputs on the IRF640 is ~0 volts (0.0013 ish), looks mostly OK.
I've removed both of the negative phase IRF640 mosfets, and still read the ~28 volts at the gate input for that phase.
I've traced the gate drive for the mosfet pair off to some surface mount transistors and what look to be power transistors, I checked a few diodes and the area, didn't find anything unusual...
I am a bit stuck how to proceed?
Thanks for any advice
Jonathan
I'm posting to see if anyone would be able to help me out. I have some basic repair knowledge with electronics and have somewhat successfully fixed amplifiers in the past before, but I'm am stuck here. I'll try to describe below what I've checked so far, forgive me for any technical/naming errors ...
This amplifier is a class D, mono output, and when powering on (energize rem line with 12v), the amp acts like one of the output's are shorted on - there is a loud pop and the sub immediately moves to the max travel, reading voltage over the sub is about 38v negative. (referring to the + / - for speaker hook up), and obviously things get hot quick. I initially jumped the gun and assumed the output mosfets were burned and tried replacing all 4, to no such luck.
The amplifier has 2 internal rails, which feed into 2 groups of 2 IRF640's for the final audio output. From what I can tell there looks to be a positive and negative phase.
At idle (no audio signal), I've measured the voltage input to pair of gate inputs on of IRF640 for what I coined the negative phase to be +~28 volts. This one I suspect there is a problem with as the speaker output is also negative when at idle (more below)
At idle, the voltage input at the positive phase gate inputs on the IRF640 is ~0 volts (0.0013 ish), looks mostly OK.
I've removed both of the negative phase IRF640 mosfets, and still read the ~28 volts at the gate input for that phase.
I've traced the gate drive for the mosfet pair off to some surface mount transistors and what look to be power transistors, I checked a few diodes and the area, didn't find anything unusual...
I am a bit stuck how to proceed?
Thanks for any advice
Jonathan
Has anything been done between the time that the amp was working properly and the time when you began troubleshooting this problem?
With the low-side FETs out of the amp, is the DC on the speaker terminals gone?
With the low-side FETs out of the amp, is the DC on the speaker terminals gone?
Hi Perry
thanks for the reply - I can't say for sure, as I bought the amplifier broken thinking I could fix it...
I've done the following:
Remove and verify the 4x huf75339p on the primary side of the coil for the step up
Verify the TO220 diode packages STTH2002CT and one other diode array (don't have the pn handy).
Thanks,
Hi Perry
Gah, though I put that in there...:banghead:
Yes, with the fets out , DC on speaker terminals is gone
Jonathan
Gah, though I put that in there...:banghead:
Yes, with the fets out , DC on speaker terminals is gone
Jonathan
Do all of the op-amps have both positive and negative supply voltage on them?
When measuring the drive voltage for the output transistors, you have to place the black probe on leg 3 and the red probe on leg 1.
When measuring the drive voltage for the output transistors, you have to place the black probe on leg 3 and the red probe on leg 1.
Hi Perry
thanks, I need to do a little digging to find and check all the OP amps... will get back to you shortly.
Will also check black on leg3 and red on leg1 of the output transistors - IRF640's -
Question - Should I put the 2x IRF640 back in to make this measurement on that phase?
Jonathan
thanks, I need to do a little digging to find and check all the OP amps... will get back to you shortly.
Will also check black on leg3 and red on leg1 of the output transistors - IRF640's -
Question - Should I put the 2x IRF640 back in to make this measurement on that phase?
Jonathan
When you checked the low-side output transistors, did you check for leakage as well as for a direct short?
There should be no continuity between leg 1 and either of the other two legs (out of the circuit) with the meter set to ohms (highest ohm range if the meter isn't auto-ranging).
There should be no continuity between leg 1 and either of the other two legs (out of the circuit) with the meter set to ohms (highest ohm range if the meter isn't auto-ranging).
Hi Perry
I need to look into how to check for leakage... I don't know how to do this but will research this.
I checked and there was no direct shorts in the mosfets themselves. Tested mosfet leg1 to the other 2 legs, result was I believe infinite ohms.
Additionally I tested the fet's using this procedure to make sure they 'switched' on OK
hxxp://www.utm.edu/staff/leeb/mostest.htm
thanks again for your help.
I need to look into how to check for leakage... I don't know how to do this but will research this.
I checked and there was no direct shorts in the mosfets themselves. Tested mosfet leg1 to the other 2 legs, result was I believe infinite ohms.
Additionally I tested the fet's using this procedure to make sure they 'switched' on OK
hxxp://www.utm.edu/staff/leeb/mostest.htm
thanks again for your help.
Hi Perry
Wow, that site has a lot of work put into it, thanks very much for your hard work in putting that up!
I checked the fets last night, all check out OK.
The 4x huf75339p
- read infinite with meter on diode test, and red on leg2, black on leg3
- read ~0.59 ohms with meter on diode test and black on leg2, red on leg3
The 4x IRF640 are all new, but tested all 4 again
- read infinite with meter on diode test, and red on leg2, black on leg3
- read ~0.55 ohms with meter on diode test and black on leg2, red on leg3
All look to be ok. I am still checking the data sheets for the following devices to provide the voltage readings for the OP amps and similar devices below:
ST 072C - Op amp
LM339 - quad comparator
LM393 - low offset voltage dual comparator
Will get the voltage measurements tonight and go from there
Jonathan
Wow, that site has a lot of work put into it, thanks very much for your hard work in putting that up!
I checked the fets last night, all check out OK.
The 4x huf75339p
- read infinite with meter on diode test, and red on leg2, black on leg3
- read ~0.59 ohms with meter on diode test and black on leg2, red on leg3
The 4x IRF640 are all new, but tested all 4 again
- read infinite with meter on diode test, and red on leg2, black on leg3
- read ~0.55 ohms with meter on diode test and black on leg2, red on leg3
All look to be ok. I am still checking the data sheets for the following devices to provide the voltage readings for the OP amps and similar devices below:
ST 072C - Op amp
LM339 - quad comparator
LM393 - low offset voltage dual comparator
Will get the voltage measurements tonight and go from there
Jonathan
Hi Perry
Hmm, found something interesting, looks like the positive supply to the OP amps is caput? I've included the measurements below, but basically the VCC measurement on the ST072C, and ST 074C op amp chips is pulled negative (-1.63) with respect to negative terminal on the amp. The LM339 and LM393 look "ok" , some are +4.5, the others are +8volts, but I am not sure if that's the expected voltage at their VCC +.
Any ideas where I can check next?
thanks,
Jonathan
Hmm, found something interesting, looks like the positive supply to the OP amps is caput? I've included the measurements below, but basically the VCC measurement on the ST072C, and ST 074C op amp chips is pulled negative (-1.63) with respect to negative terminal on the amp. The LM339 and LM393 look "ok" , some are +4.5, the others are +8volts, but I am not sure if that's the expected voltage at their VCC +.
Any ideas where I can check next?
Code:
U401 ST072C (op amp)
pin# pinID voltage
pin1 output1 -4.5
pin2 inverting input1 -0.1
pin3 non-invert input 1 -0.9
pin4 vcc - -15.9
pin5 non invert input 2 -0.2
pin6 inverting input 2 -0.75
pin7 output 2 -1.03
pin8 vcc + -1.61
U30 (slight discolor) ST072C (op amp)
pin# pinID
pin1 output1 -1.05
pin2 inverting input1 -1.04
pin3 non-invert input 1 0.03
pin4 vcc - -15.9
pin5 non invert input 2 0.0037
pin6 inverting input 2 -1.03
pin7 output 2 -1.04
pin8 vcc + -1.63
U11 (slight discolor) ST072C (op amp)
pin# pinID
pin1 output1 -2.18
pin2 inverting input1 -1.92
pin3 non-invert input 1 -1.6
pin4 vcc - -16.01
pin5 non invert input 2 2.06
pin6 inverting input 2 -2.1
pin7 output 2 -4.66
pin8 vcc + -1.62
U203 LM339 - low voltage quad comparitor
pin# pinID
pin1 output2 7.7
pin2 output1 0.6
pin3 VCC + 8.2
pin4 input 1- 3.45
pin5 input 1+ 3.4
pin6 input2- 0.7
pin7 input2+ 3.4
pin8 input 3- 2.5
pin9 input 3+ 4.97
pin10 input 4- 4.97
pin11 input 4+ 4.9
pin12 GND 0.1
pin13 output4 4.7
pin14 output3 4.7
U31 ST 074C
pin#
pin1 output1 -1.7
pin2 inverting input1 -1.69
pin3 non invert input 1 -1.51
pin4 VCC + -1.65
pin5 non invert input 2 0.003
pin6 inverting input 2 -1.3
pin7 output 2 -1.29
pin8 output 3 -1.05
pin9 inverting input 3 -0.89
pin10 non invert input 3 -0.61
pin11 VCC - -15.97
pin12 non invert input 4 -1.03
pin13 inverting input 4 -1.4
pin14 output 4 -1.36
U201 LM393 linear amp
pin#
pin1 output 1 0.01
pin2 input 1 - 0.14
pin3 input 1 + 0.8
pin4 GND 0.01
pin5 input 2 + 4.2
pin6 input 2 - 4.2
pin7 output 2 0.1
pin8 VCC 4.345
U202 LM393 linear amp
pin#
pin1 output 1 4.6
pin2 input 1 - 0.3
pin3 input 1 + 1.7
pin4 GND 0.003
pin5 input 2 + 0.15
pin6 input 2 - 2.53
pin7 output 2 0.34
pin8 VCC 8.2Jonathan
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