I have an amp I am having trouble with. It had all blown power fets, burnt gate resistors on the power fets and bad drivers; however, the output fets appaired fine using a greenlee dmm, not shorted out. I replaced all the bad components, put power to the amp, and immediately fried 1 bank of power fets. All else still checks out fine. Any suggestions. I am going to replace bad power fets and remove outputs and see what happens. I do not have an oscilloscope to test with so I am stuck with a dmm for now.
I think you mean 1100.1d.
Remove all PS FETs and before installing new ones, check the drive circuit drive voltages. They should be virtually identical for both banks from the driver IC to the gate pads for the FETs.
In the future, have all FETs clamped and insert a 100w 2 ohm current limiting resistor in the B+ line. This will prevent damaging the FETs.
Remove all PS FETs and before installing new ones, check the drive circuit drive voltages. They should be virtually identical for both banks from the driver IC to the gate pads for the FETs.
In the future, have all FETs clamped and insert a 100w 2 ohm current limiting resistor in the B+ line. This will prevent damaging the FETs.
Thanks Perry. I need to get a resistor to limit power. I always clamp fets before applying any power. I am showing 3.84 volts on each side of the power gate resistor with the power fets removed. I have 47 ohm metal film resistors in place which I believe to be the correct value. All 8 were burnt but 7 of the read near 47 ohms while 1 showed 29 ohms. Shouldn't there be a voltage drop acros the resistor? Could it be the metal film resistors in place of carbon resistors? Maybe I have the wrong sized gate resistors. I did substitute irf50n06 for the irfz44n that were original to the amp. Any further insight?
You won't have any voltage drop without a load on the FET side of the gate resistor.
Are you saying that with good gate resistors in place that the drive voltage for both banks of FETs is identical?
Do you have any 1k (or close) resistors on hand that you could use to load the gate drive? You only need 1.
Are you saying that with good gate resistors in place that the drive voltage for both banks of FETs is identical?
Do you have any 1k (or close) resistors on hand that you could use to load the gate drive? You only need 1.
Yes, the voltage on both banks was near identical. They started at 3.84 volts and climbed to 3.51 on the bank that blew out all 4 fets after replacing and 3.55 on the side that seen no issues. I used 1/2 watt 47ohm rsistors and had to replace all 8 as all 8 were burnt as well as all 8 fets. I am assuming lack of voltage as the outputs are not shorted. How do I use a 1k resistor to load the gate?
Connect it between the gate pad and source pad (pads 1 and 3) and then measure the voltage across the resistor.
Then connect between gate and drain and measure the voltage across the resistor AND measure the voltage across pads 1 and 3. .
The voltage should be very nearly identical for both banks for both resistor configurations.
Then connect between gate and drain and measure the voltage across the resistor AND measure the voltage across pads 1 and 3. .
The voltage should be very nearly identical for both banks for both resistor configurations.
On bank 1 which did not blow the fets after replacing, the gate resistor showed 3.84 volts before gate resistor and 3.62 volts when the load resistor was placed betweenpads 1 (gate) and 3; however it jumped to 4.65 before gate resistor and 4.52 when load resistor was placed on gate and drain. On bank 2 which blew the fets after replacing, I had 3.82 before gate resistor and 3.61 after gate resistor when load was placed between 1 and 3 and had near identical numbers when load was replaced between gate and drain; however, I noticed the a1275 driver seemed to warm up quickly on bank 2 and remained cool on bank 1.
If one side had a significant increase measured from 1-3 when the 1k resistor was connected between 1 and 2, that side would appear to have a defective PNP driver transistor or a bad connection between the PNP driver transistor's collector and ground.
I checked the traces and components around the driver transistors. They appair to be fine. One thing of note is that the thermal protector is tied in to the gate resistor of bank 1 and that the trace after the thermal has signs of overheating as the sealer has flaked off. Not sure how to trace that. Also the drivers follow back to a ower assembly board (pwab) and go straight to an op ic designated ic1. However, the factory for some reason ground the part number off of the ic. I think this is where my problem is. Any ideas of what it is? I don't know how to post a pic of the pwab on here.
Post a photo of the thermistor connection to a gate resistor.
Post a photo of the IC and board that you need ID'd.
Post a photo of the IC and board that you need ID'd.
How can I post a pic? I see the clip attachment in the reply section. I am on my cell phone and the pictures are on it as well.
Is ic1 a tl494 then? That is what I was thinking it was. Anything else I should look for on the board?
Yes, I looked it up. Pins 9 and 10 are feeding to the driver circuits. I am not sure how I can test it though. I do have a good tl494 from another amp.
It's not likely defective.
What's the resistance from the collector of each PNP driver to ground?
What's the resistance from the collector of each PNP driver to ground?
What else can I look for then? Drivers were new nte, new gate resistors and new fairchild 50n06 fets. I did try a quick power up with no outputs in it. With power hooked up and no remote, seen .5 amp draw. When remote was hooked up I shut down supply when amos started to climbn was at 7.56 amps when I **** down power.
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