Apologize for the late answer.......pin3 seems to go to a sot-23 schott-diode
Measured voltages from ampFET pins - FET´s not installed and marked them into ppallis picture:
Measured voltages from ampFET pins - FET´s not installed and marked them into ppallis picture:
I have inductor out of the circuit and there´s a 34VDC on the other ´leg´ of it :/ the one in the middle of the picture below red text -48,6
All measurements have been made against power supply ground
All measurements have been made against power supply ground
The diode isn't driving the IC. Does it go back to an op-amp or comparator output?
You cannot troubleshoot this amp with the inductor out if it's like similar amps. The feedback is taken from the speaker terminals which is on the output side of the inductor. If you could find what's driving the IC, you may be able to solder a bridge between the output and inverting terminals (I've never tried but it may work) to allow the amp to function at a basic level without the inductor if you believe that it's shorted.
You cannot troubleshoot this amp with the inductor out if it's like similar amps. The feedback is taken from the speaker terminals which is on the output side of the inductor. If you could find what's driving the IC, you may be able to solder a bridge between the output and inverting terminals (I've never tried but it may work) to allow the amp to function at a basic level without the inductor if you believe that it's shorted.
Äh...stupid me 😀 Yes it goes down to that LM311 (below IRS in the picture)......is there any tricks I could do to get this working, this is my own amp and it wouldn't matter if all protection circuits were disabled.
What happens if you connect a jumper from pin 7 to 3 on the 311?
Do you get a square wave on the output transistors?
Do you get a square wave on the output transistors?
My advice is to remove power mosfets, connect inductor to pcb and remove R190 (over D40-41) to disable DC protection. This way i hope you get green led on. Then measure voltage to pin 4 and 8 of LM311 - ref to gnd. Then measure voltage to emitter Q23 ref to S of the mosfet to the right position in the picture (S is the terminal to the left of three and is connected to negative vbus). Correct values are in the range of 12-15V for all three measures.
🙂
Removed R190 and gate resistors from power mosfets, red light stays on. Did I understood right that you did mean power fets, not output fets - they have been out of circuit all the time.
Measured voltage on LM311 between pins 4 and 8, 0,050VDC - measured against ground terminal, both pins read about 0,5VDC
Voltages to emitter q23 (if I understood right) something around 1,1VDC.....but not really sure if I did measure the right way.
Sorry, my mistake, i mean output mosfets, not power supply mosfets.
However, NEVER remove gate resistor instead of mosfet, never! Mosfet is not like a transistor...
Wath do you mean...''they have been out of circuit all the time'' ?
Before my last reply, do you have tried to turn on the amp without out mosfets ?
(amp goes into protection If you remove output mosfet).
My last reply means : ''remove dc protection in order to get green led on, then check for power supply voltage''.
If red led is still ON, the power supply is turned off by protection system, so we have to disable all protection of the amp before make voltage measurements.
Please let me know the situation from the beginning. I hope you understand D class amps are sometime hard to repair so i need all information you can give
However, NEVER remove gate resistor instead of mosfet, never! Mosfet is not like a transistor...
Wath do you mean...''they have been out of circuit all the time'' ?
Before my last reply, do you have tried to turn on the amp without out mosfets ?
(amp goes into protection If you remove output mosfet).
My last reply means : ''remove dc protection in order to get green led on, then check for power supply voltage''.
If red led is still ON, the power supply is turned off by protection system, so we have to disable all protection of the amp before make voltage measurements.
Please let me know the situation from the beginning. I hope you understand D class amps are sometime hard to repair so i need all information you can give
Heh.........hmm, I have NOT tested it with output mosfets in circuit after I replaced LM311 and IRS - didn´t even cross my mind that these won´t start up without output fets 😛
However, rail voltages (+/-48VDC) has been there all the time.
I pulled out pin2 of IRS -> green light goes ON ........ so we will see if it produces audio after I install output fets, if so - I´ll solder pin2 back and pray 😀
Thank you PPalli for your fast replying 🙂
However, rail voltages (+/-48VDC) has been there all the time.
I pulled out pin2 of IRS -> green light goes ON ........ so we will see if it produces audio after I install output fets, if so - I´ll solder pin2 back and pray 😀
Thank you PPalli for your fast replying 🙂
Last edited:
Okay......output fets in circuit, green light, no output
E: soldered pin2 back, green light, no output - red light after few minutes
Draws current 540mA, 0,5VDC on speaker output......goes down to 0,030VDC if 100ohm resistor installed to speaker output
E: soldered pin2 back, green light, no output - red light after few minutes
Draws current 540mA, 0,5VDC on speaker output......goes down to 0,030VDC if 100ohm resistor installed to speaker output
Last edited:
now you have pin 2 connected, output fet connected, output inductor connected (i think everything connected): ok
green led on, so now you can make voltage measurement (as i said before) but first of all, check for square wave before output inductor.
green led on, so now you can make voltage measurement (as i said before) but first of all, check for square wave before output inductor.
Yes, I have pin2 connected, output fets connected, inductor connected, everything......green led WAS on - unfortunately turned back to red :/ I´ll try if it wakes up again by removing pin2
I have to correct my statement, that output level was the same as input -> 1V/50hz in - 1V/50hz out
... so now you can make voltage measurement (as i said before)
if you removed pin2 AND R190 and green light, one step at time, no input signal:
measure voltage to pin 4 and 8 of LM311 - ref to gnd. Then measure voltage to emitter Q23, ref to S terminal of the mosfet, the right one of the two in the picture (S is the terminal to the left of three and is connected to negative vbus).
Correct values are in the range of 12-15V for all three measures
If green become red, no measurements are possible so we need to remove some other protection
If something is not clear, i'll try to explain measurements in a better way
if you removed pin2 AND R190 and green light, one step at time, no input signal:
measure voltage to pin 4 and 8 of LM311 - ref to gnd. Then measure voltage to emitter Q23, ref to S terminal of the mosfet, the right one of the two in the picture (S is the terminal to the left of three and is connected to negative vbus).
Correct values are in the range of 12-15V for all three measures
If green become red, no measurements are possible so we need to remove some other protection
If something is not clear, i'll try to explain measurements in a better way
Hi ppalli, I saw this post from you but picture is not longer available, I melted D40 and D41, I want to replace them but I have to know in which direction diodes goes. Do you still have the picture? Thanks
Hi ppalli, can you help me with repair of same amplifier. I bought it broken. There were malfunction of DC caps C91, C93, output mosfet Q27,Q28, irs20957 and lm311. All parts were replaced with new one. Now when I try to starting up the amplifier it has protection mode and red led is lighting. DC rail about +-55Vdc. When I unsolder lm311 the amplifier is starting up and led is green and the other way when i solder back lm311 and unsolder irs20957 I got same led is green but when both solder the amplifier is in protection mode and got some squeak sound in output inductor. Can you send part of schematic diagram with irs and lm311 to checked all passive component and zener diod. Also I replaced lC5 and IC10 with new one.