I have viewed several great and very informative posts already here on the site regarding my exact amp. Even have noted some of the exact same issues with mine that I know will need fixing.
My first initial question is my gate resisters on the PWR fets are toast of course as seen on many here already. I noted these are 47 ohm resistors I believe Mr. Perry stated in another post. Mine however are not through hole type like I have seen here but mine are surface mount or where I should say they where really smoked! pretty much all crumbled off the board.
Anyway they said 470 on the tops of them but they are only 47 ohm? and Question 2 is one of the pads on at least 1 of the bad resistors surface mount area looks like it was completely burned off and there is nothing left for me to solder a replacement too? What can I do in this case? Wishing mine where through put at this point. Any and all advise would be great! So R605s left Pad looks the worst out of all of them again not even sure what to do with that flux and dab of solder or?
Now below this text here is from another JL Audio 250/1 amp where they are using surface mount Resistors as well but they say 470 on them is that still a 47ohm resistor or 470ohm? Sorry for the dumb questions new to this repair thing but find it very interesting! And would love to fix my amp. Also the 2 amps are using the same fets for PWR IRFZ44N which I saw in another post Perry suggests replacing with IRF3205s so will be doing that! Thanks for taking time to review this and for any help guys/gals!
My first initial question is my gate resisters on the PWR fets are toast of course as seen on many here already. I noted these are 47 ohm resistors I believe Mr. Perry stated in another post. Mine however are not through hole type like I have seen here but mine are surface mount or where I should say they where really smoked! pretty much all crumbled off the board.
Anyway they said 470 on the tops of them but they are only 47 ohm? and Question 2 is one of the pads on at least 1 of the bad resistors surface mount area looks like it was completely burned off and there is nothing left for me to solder a replacement too? What can I do in this case? Wishing mine where through put at this point. Any and all advise would be great! So R605s left Pad looks the worst out of all of them again not even sure what to do with that flux and dab of solder or?
Now below this text here is from another JL Audio 250/1 amp where they are using surface mount Resistors as well but they say 470 on them is that still a 47ohm resistor or 470ohm? Sorry for the dumb questions new to this repair thing but find it very interesting! And would love to fix my amp. Also the 2 amps are using the same fets for PWR IRFZ44N which I saw in another post Perry suggests replacing with IRF3205s so will be doing that! Thanks for taking time to review this and for any help guys/gals!
Welcome to diyAudio. I will move your post to the Solid State forum.”470” is using numbers for the resistor color code. Yellow, purple, black. 4, 7 followed by zero zero’s. That is in the right range for a resistor in series with a mosfet gate.
They do this with capacitors too. Sometimes, but not all - which means you have to measure it to be sure.
They do this with capacitors too. Sometimes, but not all - which means you have to measure it to be sure.
Hello guys and thank you for the reply! Makes sense now 🙂
Do you think that left pad on R605 in the first picture will be ok? Should I just put some flux down then solder in the new resistor?
Do you think that left pad on R605 in the first picture will be ok? Should I just put some flux down then solder in the new resistor?
use your meter to make sure there is contact from that pad to the gate of the mosfet - if so, then you should be able to solder in the resistor. If not, then you will need to "modify" the resitor placement to reach from the Gate to the other pad, OR sodler to the good pad and run a wire to the gate pin of the mosfet. Either wway you go, use your meter to make sure the resistor is making good contact to the correct location on both sides, BEFORE you apply any power, or you could be doing this job again.
Good advice from @bullittstang.
Of course you have to resolve the defect that led to the smoked resistor to avoid new smoke. Most likely a failed transistor connected to R605, but there could be collateral damage to other parts.
Good luck!
Of course you have to resolve the defect that led to the smoked resistor to avoid new smoke. Most likely a failed transistor connected to R605, but there could be collateral damage to other parts.
Good luck!
Well thanks again guys for the advice here. Actually found 2 out of the 16 pads that where smoked! Was able to run traces to those 2 so we should be good but will respond once everything is soldered in and pwr up. Great Forum thanks again!
Good afternoon fellow DIY'ers! So probably a super easy silly question but I ordered some 47 ohm SMD resistors from Digikey they came in and holy smokes they are super tiny and the WRONG size lol What size do I need and how do you differentiate or measure for the correct size for the future and my knowledge. 🙂
Thanks in advance sorry for the noob questions!
Thanks in advance sorry for the noob questions!
Well Did some research/Measuring and I came up with either 1206 if using inches or a 3216 if using mm. I must have ordered 0603mm's lol they where tiny guys
Is this normal for amps in general to read a value on multimeter continuity test then go open? See video link file was large sorry: https://drive.google.com/file/d/1sNbsKSHjWUE4a0jgOs0QNfJjgZufJ7mD/view?usp=drivesdk
Hi do you have a circuit diagram? See you already taken the IRFZ44N Mosfets out. Do you know why the amp failed? Maybe speaker wiring short circuit?
Typically short circuit will destroy Mosfets they go short circuit between Source and Drain and put too much voltage on the Gate as they go short circuit so the Gate resistor burns out. Sometimes the Drain is shorted to the Positive supply and the Mosfet cannot survive. Sometimes the 12V polarity is reversed and the Mosfets cannot survive that. Must be quite an event to take out several Mosfets together. Suggest you have info about why the Amp failed if you can.
Typically several IRFZ44N are connected in parallel but each has a separate drive to the Gate - but if one fails and burns they all do.
How many IRFZ44N connected in parallel? They will be able to carry a LOT of power/current in parallel. If one IRFZ44N decided to fail on its own the others would be OK but all went so hard to blame the IRFZ44N.
Yes you can replace IRFZ44N with IRF3205 but why would you do that? Download the datasheets and compare them. yes the IRF3205 can handle more current but the Gate capacitance is double that for IRFZ44N, that makes the IRF3205 harder to drive and likely slower. The IRF3205 can handle more avalanche energy than IRFZ44N but your amp had some trauma and unlikely avalanche energy would have saved IRF3205 either.
I have seen a lot of IRFZ44N used by Victron Energy for their big 12 Volt to 230V 5KVA Inverters that go on ships, they connect lots of them in parallel.
Because the Gate resistors burned its possible that whatever circuitry that drives the Gate resistors is also damaged. Find out the driving circuit (maybe IC) and get datasheet and evaluate how well protected it is, better still test the Gate driver circuit.
When you start replacing the resistors and IRFZ44N consider only fitting one IRFZ44N at first and testing carefully with a light load. Is there another channel is that OK?
How about the Power Supply circuitry is any damage there? Probably good idea to know that the power supply is OK before replacing any IRFZ44N.
JX500/1d specifications:
Amplifier Topology: Class D
Power Supply: Unregulated PWM switching type
So the Power Supply switches the 12V up to a higher voltage for the amp to supply more Watts. Try to power up the amp 12V from a bench power supply limiting the current to say around 100mA at first, with no Mosfets the amp supply current should be low. Check the PWM Switching is giving the higher voltage and is not damaged.
Try to get circuit diagram for the amp.
Last edited:
Will definitely read up as I am very green to amp repair and appreciate all the advice here! Why the damage not sure it was given to me because it was "blown" Figured only 1 way to start learning similar to my first engine tear down and rebuild take it apart research, read, read some more learn make mistakes and relearn! Finally I have a running engine with zero issues years later. But I had to start somewhere. 🙂
Awesome information here thank you!!
Good attitude and well done, you have a good chance of repairing the amp so work carefully.
Low voltage high current amps using 12 Volt are very unforgiving if something gets shorted out, work carefully.
The DC PWM switching part of the supply knocks the voltage up to maybe 35 Volt or more, the output of the amp needs more than 12 to drive any power into a speaker.
There is plenty of info about these amps on this forum and elsewhere.
Low voltage high current amps using 12 Volt are very unforgiving if something gets shorted out, work carefully.
The DC PWM switching part of the supply knocks the voltage up to maybe 35 Volt or more, the output of the amp needs more than 12 to drive any power into a speaker.
There is plenty of info about these amps on this forum and elsewhere.