Remote terminal 11.65V. Same as the kenwood amp it's in parallel with and working fine.
Pin 9 is 4.25V. Pin 10 is 4.17V. ( this IC doesn't have a notch like I'm used to seeing at one end but, it does have a line which I believe is pointing at pin 1.)
Pin 9 is 4.25V. Pin 10 is 4.17V. ( this IC doesn't have a notch like I'm used to seeing at one end but, it does have a line which I believe is pointing at pin 1.)
The drivers may have failed. Do you about 12v on the collectors of the NPN power supply driver transistors?
I may have to study your tutorial some more because I'm not sure where to measure that?
Q4 and Q5 are the NPN drivers.
The collector is the terminal that's by itself on the top of the transistor.
The collector is the terminal that's by itself on the top of the transistor.
You should have a bit less voltage on the emitter terminals of the driver transistors than you did on pins 9 and 10 of the 494.
I assume we are still talking Q4 and Q5. One terminal of Q4 is 4.29V The other is 0V. Q5 one is 4.20V. The other is 3.8V. In each case, that is L to R with the collector on top.
The driver with 0v on the right leg is defective.
For the other driver, you should have the 3.8v on the gate leg of the power supply FET.
For the other driver, you should have the 3.8v on the gate leg of the power supply FET.
I had a feeling you were going to say that when I measured 0V especially given the other one had voltage on both legs. So is the right leg the emitter? The left pin on Q6 is the one that had 0.96V. Q7 had nothing. 0.96 isn't close to 3.8. Do I have more problems than just the one defective driver?
If the gate resistor has 3.8v on one leg and 0.96 on the other leg and the resistor is within tolerance, the FET has likely failed. It could have happened when the amp was powered up in the vehicle or could have been damaged when you tinned the back of it. If you remove the gate resistor, you should read infinite resistance from leg 1 of the FET to either other leg.
Don't reconnect B+ to the amp until you confirm that all of the drive circuit is OK. This will be done with only remote and ground connected.
If you don't have the drivers, you'll have to get them before you can do anything else.
If you had a defective output transistor, there could be additional damage in the audio section as well.
Dd you check the gate resistors for the blown outputs?
Don't reconnect B+ to the amp until you confirm that all of the drive circuit is OK. This will be done with only remote and ground connected.
If you don't have the drivers, you'll have to get them before you can do anything else.
If you had a defective output transistor, there could be additional damage in the audio section as well.
Dd you check the gate resistors for the blown outputs?
Last edited:
I checked resistance across resistors for the items I replaced. The gate resistor for Q7 was fried so I replaced it.
I do indeed have 3.74V on one leg of the gate resistor for Q6 and 0.95V on the other leg.
I don't have the drivers. I will have to make another order. I also don't have any extra IRF3205's. I probably should have ordered extra of everything while I was at it. Being a greenhorn, I thought sure if I replaced everything on the two daughter boards I would be ok.
I need to try and make sure I have everything I could possibly need on the next order.
Is there a high number of other parts I may need or, likely just a few?
I see the defective driver Q4 from the sheets of the 201s and 401s you uploaded are part number MMBT3904LT1. I see at digikey, those are only around 12 cents a piece. I may as well order about 10 of those.
I see the defective driver Q4 from the sheets of the 201s and 401s you uploaded are part number MMBT3904LT1. I see at digikey, those are only around 12 cents a piece. I may as well order about 10 of those.
I'd order the MMBTA06 and MMBTA56 for the drivers in the power supply. Order at least 10 of each. They may be needed in the audio section of the amp.
What is the circuit board designation for the IRF540 that failed?
Don't order anything until we do some more troubleshooting.
In the future, don't change anything that doesn't need to be replaced. In an amp like this, it's possible to damage parts like the outputs by soldering the backs of the transistors and changing parts that aren't definitively defective could cause more problems than they need to. In an amp where you want to replace parts that are not defective, get the amp working perfectly, then replace the other parts. Then, if the amp doesn't work after replacing those parts, it reduces the amount of troubleshooting needed to find the fault.
For any of the FETs that you have to tin the backs on, check them before installing them in the board. At the very least, confirm that you still read infinite resistance between the gate leg and the other two legs.
What is the circuit board designation for the IRF540 that failed?
Don't order anything until we do some more troubleshooting.
In the future, don't change anything that doesn't need to be replaced. In an amp like this, it's possible to damage parts like the outputs by soldering the backs of the transistors and changing parts that aren't definitively defective could cause more problems than they need to. In an amp where you want to replace parts that are not defective, get the amp working perfectly, then replace the other parts. Then, if the amp doesn't work after replacing those parts, it reduces the amount of troubleshooting needed to find the fault.
For any of the FETs that you have to tin the backs on, check them before installing them in the board. At the very least, confirm that you still read infinite resistance between the gate leg and the other two legs.
Thank you for all of the help Perry. I'm working today (12 hour shifts) so I won't be home til late. I thought you meant it was IRF3205 that was faulty. That was Q6 I think. It was that gate resistor I measured the voltages on per your instructions. It sounds like I need to go back and check the 540's?
The 3205 appears to be dragging the drive voltage down. It should not if it's not shorted or leaky.
You can check the 540s. There are several things that need to be done before ordering parts.
You can check the 540s. There are several things that need to be done before ordering parts.
Should I check at the gate resistors by the 540's in the same manner as the IRF3205?
Just for giggles, I hooked up my 12V Dewalt drill battery to the amp. I had a solid 12V on the remote terminal. I repeated some measurements you had me do such as pins 9 and 10 of the TL494. The results were very similar to those in the truck.
I tested the pins on the 540s. On pins 1 and 3 (left to right with the tab on top) I had 0.35V on both 540s. For whatever that is worth. Board designations were R152 and R252. Q115 and Q215 on the FETs.
I tested the pins on the 540s. On pins 1 and 3 (left to right with the tab on top) I had 0.35V on both 540s. For whatever that is worth. Board designations were R152 and R252. Q115 and Q215 on the FETs.
Last edited:
"I had 0.35V on both 540s."
Do you mean that you had your meter set to diode-check and read 0.35v or do you mean that you had the amp powered up and read 0.35v with the meter set to DC voltage?
With the power supply blown, you can't really trust DC readings on the secondary side of the power supply. With only remote and ground connected, there will be essentially no secondary voltage.
Do you mean that you had your meter set to diode-check and read 0.35v or do you mean that you had the amp powered up and read 0.35v with the meter set to DC voltage?
With the power supply blown, you can't really trust DC readings on the secondary side of the power supply. With only remote and ground connected, there will be essentially no secondary voltage.
- Status
- Not open for further replies.