Hello, I am currently trying to repair a Memphis Audio Pr1x1000 amp. I think I have narrowed down the problem to a short somewhere near the transformer, (I think). And I am trying to rule out the transformer as the problem, but I dont exactly know how to test the transformer, I am getting a couple of shorts on the transformer, but I dont know if that is normal or not, I can leave a photo of what is shorted together. Can someone help me figure out what should, and shouldnt be "shorted" on the transformer?
Some things I have done:
I thought it might be a mosfet/transistor, but I pulled all the transistors, and the short was still there, and all the transistors seem to be in working condition, (from what I can tell)
I used some IPA around the board to check for hot spots, and two diodes and a small capacitor were getting hot when the amp was powered on, so I pulled them, and the transformer seems to be shorted still, unless what Im seeing continuity on is normal. (You should be able to see the diodes in the photo, they are the ones slightly askew as I put them back on the board)
I also found an IC that was getting warm, a IRS2092S (op amp?) but when I pulled it, the transformer still has those "shorts"
I tried hooking my multimeter in continuity mode to the "shorts" on the transformer, and wiggling wires to see if it would stop or change, but it didnt
Idk, but at this point im lost, and just wondering how to make sure my transformer is good, or what else I should be checking.
Any help is much appreciated.
Some things I have done:
I thought it might be a mosfet/transistor, but I pulled all the transistors, and the short was still there, and all the transistors seem to be in working condition, (from what I can tell)
I used some IPA around the board to check for hot spots, and two diodes and a small capacitor were getting hot when the amp was powered on, so I pulled them, and the transformer seems to be shorted still, unless what Im seeing continuity on is normal. (You should be able to see the diodes in the photo, they are the ones slightly askew as I put them back on the board)
I also found an IC that was getting warm, a IRS2092S (op amp?) but when I pulled it, the transformer still has those "shorts"
I tried hooking my multimeter in continuity mode to the "shorts" on the transformer, and wiggling wires to see if it would stop or change, but it didnt
Idk, but at this point im lost, and just wondering how to make sure my transformer is good, or what else I should be checking.
Any help is much appreciated.
With all due respect, if you have to ask how to do it, take it to a competent engineer for your own safety.
The IRS2092 is the class D driver, not an op amp) and runs slightly warm normally.
Remove the transformer, (other components may skew your readings) and consult the manufacturers data sheet on it. It suffices to say, you need a service manul/service information diagram sheet to be able to work out what is going on.
The IRS2092 is the class D driver, not an op amp) and runs slightly warm normally.
Remove the transformer, (other components may skew your readings) and consult the manufacturers data sheet on it. It suffices to say, you need a service manul/service information diagram sheet to be able to work out what is going on.
Im sorry but I dont have enough money to pay someone else to fix it for me.
And I would like to learn about how to repair things like this and im not ever going to learn if I dont try.
And well thank you for that info.
And I would like to learn about how to repair things like this and im not ever going to learn if I dont try.
And well thank you for that info.
These pins that you are referring bro. They are showing short on your multimeter, but none of them are short. You can check the torodial with an inductance meter. But short of a transformer is a rare chance. Remove all the fets from supply and audio section. Then clean all your prints ( bcz higher possibility that you soldered two prints on pcb and joint them) Send me images. I will definitely help you with this.
Ok makes sense because they are just pieces of wire connected together after all, but I just wasnt sure if the bigger wire, and the small wire should be electronically connected together like that.
I dont have an inductance meter, but I do have a cheap oscilloscope on the way that should be here on monday, (just a cheap handheld one). Ill have to consider getting an inductance meter also.
And I dont think I left any solder bridges because I checked with the multimeter each time that I soldered to make sure I didnt bridge anything together.
BUT,
I was continuing to do a visual inspection on the board, and I did find what looks to be a missing resistor (R178), I am not sure if it is a missing resistor or just an intentionally un-populated spot for a resistor, its just weird because its right next to the IRS2092 chip, so it seems odd that it would be populated, but there is other spots on the board that were left intentionally unpopulated, so im just not sure.
From the IRS2092 datasheet, (if I got my pin ordering correct) it looks to be pin number 9, a "DT" pin, but I dont even know what that means, it says Input Voltage pin, but Im not sure if this pin was intentionally not used or what. It looks like there SHOULD be a resistor there because there is a capacitor right on the other side of where the resistor "should" be.
I will put up a photo of the "missing" resistor, and if someone could let me know if there should or shouldnt be a resistor there I would appreciate it.
I dont have an inductance meter, but I do have a cheap oscilloscope on the way that should be here on monday, (just a cheap handheld one). Ill have to consider getting an inductance meter also.
And I dont think I left any solder bridges because I checked with the multimeter each time that I soldered to make sure I didnt bridge anything together.
BUT,
I was continuing to do a visual inspection on the board, and I did find what looks to be a missing resistor (R178), I am not sure if it is a missing resistor or just an intentionally un-populated spot for a resistor, its just weird because its right next to the IRS2092 chip, so it seems odd that it would be populated, but there is other spots on the board that were left intentionally unpopulated, so im just not sure.
From the IRS2092 datasheet, (if I got my pin ordering correct) it looks to be pin number 9, a "DT" pin, but I dont even know what that means, it says Input Voltage pin, but Im not sure if this pin was intentionally not used or what. It looks like there SHOULD be a resistor there because there is a capacitor right on the other side of where the resistor "should" be.
I will put up a photo of the "missing" resistor, and if someone could let me know if there should or shouldnt be a resistor there I would appreciate it.
I don't think that there has been a resistor there. And if mosfets and other parts showing shorting, than this resistor can't cause that. You can do this repair by doing step by step. At first remove all the power supplie fets and check PWM on gate on each mosfet of supply section. Then if its coming, take 2 mosfets ( check with multimeter that they are not short and working) place each on push and pull side. Than check if the rail voltage is coming or not. For check the rail voltage, you should have to remove all the fets from audio section. If rail voltage is coming, than check the low and high side outputs first from irs2092 and than at the mosfets. Divide amp into parts. Be patient, do all the things carefully. It will definitely work. In 80-90 % chances mosfets in audio and supply section is the main cause of failure of an amp.
Upload images of full pcb and amplifier.
At the end if you want that it will work well in the future, replace all the mosfets, pwm ic ( tl 494) any buffer transistor and class d driver ( irs 2092s)
At the end if you want that it will work well in the future, replace all the mosfets, pwm ic ( tl 494) any buffer transistor and class d driver ( irs 2092s)
Thanks for your help. Heres where Im at. Iv pulled all the transistors/mosfets, and am waiting for my oscilloscope to arrive so I can check for PWM on the gates of the power supply section. (That should be Monday, maybe Tuesday).
Ive also ordered some new main 80v 2200uf capacitors as a few of them were a bit bulgy, I pulled the worst one, and it tested it and its saying its a 1800 uf cap, but i dont know if that would cause my issue, (I dont think so).
I also ordered some new output transistors as after closer inspection they were a bit discolored from heat (they all test ok in my component tester, so I didnt think thats what my issue is), also added a new driver (IRS2092) chip to the order, as it was only a couple of bucks with my transistors.
I was going to order new power supply transistors also, but I didnt have enough money, and every one of my power supply transistors tests good with my (cheap) component tester. (Will get those later if I end up needing them).
Just some things id like to add that may be useful to know for diagnosis:
-When I first got the amp and tested it, I hooked it up to my power supply at 12v and 1 Amp, hooked my ipod up to the RCA's, and plugged in a car speaker to test for out put, and the speaker was just making a horrible high pitched wining and crackling noise.
-When I first opened the amp up, one of the output transistors had a broken leg, thinking that was surely going to be my issue, I soldered it back together, and the amp had not changed. made the same sound.
-Looked at the amp further, and found a Thermistor with a broken leg, so I soldered the leg back together, and tested it with resistance mode, and it seemed ok after that.
-At some point one of the rectifiers legs had broken off, and the person that had the amp before me soldered them back together, (the rectifiers test ok in my tester)
-Some of the main large voltage caps are bulged and have ordered new ones, (they dont seem to be shorted or anything tho, just slightly out of spec)
Unless anyone has any ideas of what I should/can do, im probably going to wait until i have my oscilloscope on Monday/Tuesday to continue troubleshooting this thing.
I appreciate the help/input guys
Ive also ordered some new main 80v 2200uf capacitors as a few of them were a bit bulgy, I pulled the worst one, and it tested it and its saying its a 1800 uf cap, but i dont know if that would cause my issue, (I dont think so).
I also ordered some new output transistors as after closer inspection they were a bit discolored from heat (they all test ok in my component tester, so I didnt think thats what my issue is), also added a new driver (IRS2092) chip to the order, as it was only a couple of bucks with my transistors.
I was going to order new power supply transistors also, but I didnt have enough money, and every one of my power supply transistors tests good with my (cheap) component tester. (Will get those later if I end up needing them).
Just some things id like to add that may be useful to know for diagnosis:
-When I first got the amp and tested it, I hooked it up to my power supply at 12v and 1 Amp, hooked my ipod up to the RCA's, and plugged in a car speaker to test for out put, and the speaker was just making a horrible high pitched wining and crackling noise.
-When I first opened the amp up, one of the output transistors had a broken leg, thinking that was surely going to be my issue, I soldered it back together, and the amp had not changed. made the same sound.
-Looked at the amp further, and found a Thermistor with a broken leg, so I soldered the leg back together, and tested it with resistance mode, and it seemed ok after that.
-At some point one of the rectifiers legs had broken off, and the person that had the amp before me soldered them back together, (the rectifiers test ok in my tester)
-Some of the main large voltage caps are bulged and have ordered new ones, (they dont seem to be shorted or anything tho, just slightly out of spec)
Unless anyone has any ideas of what I should/can do, im probably going to wait until i have my oscilloscope on Monday/Tuesday to continue troubleshooting this thing.
I appreciate the help/input guys
After looking at my own photos, I did notice a bare trace near resistor R104 on the bottom photo. And it leads to the TL494 chip you were talking about. If that trace came into contact with chassis ground (thats right where the board slides into the heat sink), would it blow/short that IC maybe?
I think you have over complicated all the things.Answer a few questions bro.
1. As you remove all the supply fets, is it showing short on +12v and gnd or at Rem and gnd?
2. If its not showing short now, then add 12v ,rem and gnd at about 2-3 amp and check with the volatge meter if the voltage on supply fets gate is coming ( bcz you dnt have scope to check pwm) a simple multimeter can check this. It should be around 3-4 volts dc on 1st pin of mosfet.
1. As you remove all the supply fets, is it showing short on +12v and gnd or at Rem and gnd?
2. If its not showing short now, then add 12v ,rem and gnd at about 2-3 amp and check with the volatge meter if the voltage on supply fets gate is coming ( bcz you dnt have scope to check pwm) a simple multimeter can check this. It should be around 3-4 volts dc on 1st pin of mosfet.
That is very possible, I overthink things all the time ha.
1. With the fets out, there no short between 12v and gnd, (just caps charging), and no short between Remote and gnd.
2. I added 12v at 2 amps, and was getting 4.5 volts on the first fet pin/pad
1. With the fets out, there no short between 12v and gnd, (just caps charging), and no short between Remote and gnd.
2. I added 12v at 2 amps, and was getting 4.5 volts on the first fet pin/pad
So great its working. So your TL494 ( PWM GENERATOR) generating pulses.
Bring new mosfets and insert only 1 in push side and 2nd in pull side. Then check if the rail voltage is coming? Insert new capacitors and also check rectifiers ( if broken legs then replace them) with new ones. Tell me after if rail voltage is stable
Bring new mosfets and insert only 1 in push side and 2nd in pull side. Then check if the rail voltage is coming? Insert new capacitors and also check rectifiers ( if broken legs then replace them) with new ones. Tell me after if rail voltage is stable
Awesome. So the "push" and "pull" would just be 1 transistor on each bank of each of the 4 power supply transistors correct?
To check rail voltage, do I measure where the output transistors would go?
And to replace the rectifiers, I cant find the exact chips, so to replace them, I just need to find ones in the same package that can handle the volts and amps right?
The current ones are 400v 20amp rectifiers.
I have been trying to find a matching set of rectifiers, and the closest matching set I can find are 600v, 30amps. Would those be alright?
Or should I just replace the one with broken legs and it doesnt matter if they match or not?
(Found a 400v, 30amp one, but couldnt find a matching set of those)
This is the rectifier with the broken legs datasheet:
https://www.alldatasheet.com/datasheet-pdf/view/1077176/THINKISEMI/FMU34S.html0
These are the replacements I was thinking of getting:
https://www.digikey.com/en/products...0?s=N4IgTCBcDaIIIAUAqBmADAEQGxoEIGE4BxEAXQF8g
https://www.digikey.com/en/products/detail/microchip-technology/apt30d60bctg/1494481
They are slightly different because one is rated for 30 amps and the other 27 amps, and they dont have the "hole" to mount them to a heat sink, but that shouldnt be an issue as long as I can mount them to the case right?
Or if its ok to mix them and have them not be a set, I was thinking of just getting this one:
https://www.digikey.com/en/products/detail/taiwan-semiconductor-corporation/HER3005PTH/18720593
(Its a 400v 30amp)
Sorry for asking so many questions, but I just havent had to find replacement components like this before and just want to make sure I understand how to do it correctly. Thanks for your help.
To check rail voltage, do I measure where the output transistors would go?
And to replace the rectifiers, I cant find the exact chips, so to replace them, I just need to find ones in the same package that can handle the volts and amps right?
The current ones are 400v 20amp rectifiers.
I have been trying to find a matching set of rectifiers, and the closest matching set I can find are 600v, 30amps. Would those be alright?
Or should I just replace the one with broken legs and it doesnt matter if they match or not?
(Found a 400v, 30amp one, but couldnt find a matching set of those)
This is the rectifier with the broken legs datasheet:
https://www.alldatasheet.com/datasheet-pdf/view/1077176/THINKISEMI/FMU34S.html0
These are the replacements I was thinking of getting:
https://www.digikey.com/en/products...0?s=N4IgTCBcDaIIIAUAqBmADAEQGxoEIGE4BxEAXQF8g
https://www.digikey.com/en/products/detail/microchip-technology/apt30d60bctg/1494481
They are slightly different because one is rated for 30 amps and the other 27 amps, and they dont have the "hole" to mount them to a heat sink, but that shouldnt be an issue as long as I can mount them to the case right?
Or if its ok to mix them and have them not be a set, I was thinking of just getting this one:
https://www.digikey.com/en/products/detail/taiwan-semiconductor-corporation/HER3005PTH/18720593
(Its a 400v 30amp)
Sorry for asking so many questions, but I just havent had to find replacement components like this before and just want to make sure I understand how to do it correctly. Thanks for your help.
Yes you can insert just 1 mosfet to each side to get things running. 1 can handle 200-300 watts and the numbers are for more load.
Your rail voltage would be on capacitors.
Your links are broken . Send me images of your rectifiers with broken legs. I will tell you the solution.
Your rail voltage would be on capacitors.
Your links are broken . Send me images of your rectifiers with broken legs. I will tell you the solution.
Ok cool.
I made another post on here asking about replacement rectifiers and people were saying that my purposed replacements should be alright, they are a slightly different mounting style, but as long as the voltage and the amps are at least rated as much as the old ones, and I can mount them to the heat sink, they should be ok.
I just wasnt sure if it was ok to replace just one, but it seems like it would be better to have a matching set.
I did solder some old component legs onto the one with broken legs to be able to use it for now, until I can get replacements. It seems to test ok.
These are the rectifiers.
I made another post on here asking about replacement rectifiers and people were saying that my purposed replacements should be alright, they are a slightly different mounting style, but as long as the voltage and the amps are at least rated as much as the old ones, and I can mount them to the heat sink, they should be ok.
I just wasnt sure if it was ok to replace just one, but it seems like it would be better to have a matching set.
I did solder some old component legs onto the one with broken legs to be able to use it for now, until I can get replacements. It seems to test ok.
These are the rectifiers.
These seems to be ok. Don't replace them for now. Attach legs from other transistors and soldered them properly with rectifiers legs. Yes you are right you can change rectifiers with 400v 30a into 600v 27a, but the diode arrows printed on these should be matched and they also in the plastic package ( if new ones not in plastic package, insert mica under new ones)
Another thing to remember, these two are different diodes, so be ensure to place on the exact place of the pcb. If you interchange them with each other, your amp will be in protection mode.
Insert these ones for now, add some new capacitors, and 1 mosfet for each bank, your rail volatge would be running. Then insert 1-1 mosfet in each audio section bank( low side- high side) and then check if the audio is coming. Tell me if you need anything else.
Another thing to remember, these two are different diodes, so be ensure to place on the exact place of the pcb. If you interchange them with each other, your amp will be in protection mode.
Insert these ones for now, add some new capacitors, and 1 mosfet for each bank, your rail volatge would be running. Then insert 1-1 mosfet in each audio section bank( low side- high side) and then check if the audio is coming. Tell me if you need anything else.
Attachments
Ok, luckily my board has the diode directions printed on it, so that shouldnt be a problem.
So with two transistors in the power supply, I get 12v on the rail. So I put the capacitor back in for now to test, put the diode rectifiers back in, and I put two transistors in the output audio section, and I get no audio out. And it seems like the amp keeps going to protect mode, cause it will cut back on the amount of volts its drawing, it will start drawing 8-9v instead of 12v.
So that means I have some type of issue with the audio output section right?
I just dont know what ha.
So with two transistors in the power supply, I get 12v on the rail. So I put the capacitor back in for now to test, put the diode rectifiers back in, and I put two transistors in the output audio section, and I get no audio out. And it seems like the amp keeps going to protect mode, cause it will cut back on the amount of volts its drawing, it will start drawing 8-9v instead of 12v.
So that means I have some type of issue with the audio output section right?
I just dont know what ha.
12v is not enough on rail. Something is missing. Either rectifier or an ac supply from torodial. I don't know the exact rail voltage of this amp but my guess it would be around 50 positive and 50 negative volts on capacitors. Protection mode can be on bcz of thermal protection and short circuit in audio section or supply section ( 90% chances ) . So check all the traces . Resolder transformer prints. And any other prints. Keep out audio mosfets, then check the rail voltage and protection mode.
I ended up getting about 38v on the rail, but the amp itself was only taking 8.5v, which doesnt seem right to me, but maybe it is normal if there isnt all the transistors installed?
Im starting to think the main rail caps are a problem (idk if they are THE problem, just a problem) because if I check for shorts on my 12v power input and Ground, if I switch the probes, (Neg probe on Pos, and Pos probe on Ground), I get a short for a really long time before the caps start charging (like a full minute). Plus a few of them are bulging quite a bit.
Im starting to think the main rail caps are a problem (idk if they are THE problem, just a problem) because if I check for shorts on my 12v power input and Ground, if I switch the probes, (Neg probe on Pos, and Pos probe on Ground), I get a short for a really long time before the caps start charging (like a full minute). Plus a few of them are bulging quite a bit.
Ok so I think ive made some progress. After poking around, I found what looked to be an almost short, on the last set of output fets pads (when they are out), they had a very low ohms reading compared to the other set of pads. So I kept trying to find what was making the ohms so low, and started removing things with my hot air and looked for an ohm change between the pads. And after a resistor or two, everything kept pointing to the IRS2092 chip, so I decided to remove it again, and what do you know, my low ohm reading was gone from between the pads. With that chip off I am getting a full 45v rail voltage (assuming thats full voltage ha). And nothing seems to be heating up.
I didnt find it at first because it wasnt a complete short and didnt show up on my continuity test, i had to use ohms mode to see it.
I stuck the chip back on just to test a little more, and when I put voltage to the board again, I decided to touch the chip with my finger, and the thing almost burned me it was so hot. I get the guy earlier said they run hot, but I doubt they run that hot.
So yeah I am getting voltage all the way to the output fets with that chip off, and nothing seems to be getting hot anymore.
I ordered that chip a few days ago when I orded the new output fets, so it should be here in a day or two probably, ill try to post if it ends up being the problem or not.
Will the amp making sound through the speaker without that chip? I feel like the chip needs to be on to test for audio
I didnt find it at first because it wasnt a complete short and didnt show up on my continuity test, i had to use ohms mode to see it.
I stuck the chip back on just to test a little more, and when I put voltage to the board again, I decided to touch the chip with my finger, and the thing almost burned me it was so hot. I get the guy earlier said they run hot, but I doubt they run that hot.
So yeah I am getting voltage all the way to the output fets with that chip off, and nothing seems to be getting hot anymore.
I ordered that chip a few days ago when I orded the new output fets, so it should be here in a day or two probably, ill try to post if it ends up being the problem or not.
Will the amp making sound through the speaker without that chip? I feel like the chip needs to be on to test for audio