I have a Orion 1200D that had some C3198 transistors blown which control the output relay. Replaced them and now when I power up the board, I do get audio, but there's 2 resistors that get really hot and the amp draws 4amps at 10V, and at 12V it's drawing 8A at idle!
All of the PSU fets are good, all of the output fets seem ok, none even get warm. None of the transistors or any other component on the driver boards or main board get hot that I can find, except two resistors which I mentioned.
I detail the resistors and output fet waveforms in images in link below - am not sure if the gate waveforms are ok and am concerned about possible slow turn-on indicated by the curve of the top and bottom of drain pin pulses.
Pictures
Orion 1200D - Album on Imgur
Appreciate any help!
All of the PSU fets are good, all of the output fets seem ok, none even get warm. None of the transistors or any other component on the driver boards or main board get hot that I can find, except two resistors which I mentioned.
I detail the resistors and output fet waveforms in images in link below - am not sure if the gate waveforms are ok and am concerned about possible slow turn-on indicated by the curve of the top and bottom of drain pin pulses.
Pictures
Orion 1200D - Album on Imgur
Appreciate any help!
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Is your probe calibrated to your scope? If not, that could cause the curved leading edge on the drains. If they are not heating up, the drive is likely OK.
The resistors are large so they can dissipate the heat. If the capacitors in series with the resistors are not shorted, replace the one that's out of tolerance. If they're causing heat stress on their solder pads, go with the next larger resistor and leave the leads longer so they cannot transfer so much heat to the board.
As a side note, I have photos of a rev2 board and they're using 22k resistors.
The resistors are large so they can dissipate the heat. If the capacitors in series with the resistors are not shorted, replace the one that's out of tolerance. If they're causing heat stress on their solder pads, go with the next larger resistor and leave the leads longer so they cannot transfer so much heat to the board.
As a side note, I have photos of a rev2 board and they're using 22k resistors.
Perry,
Thank you. My probe is calibrated, so it's not that.
I saw in another post where you said they were 22k ohms... I was considering replacing them. What are these resistors for? Would the amp be ok to test shortly with them removed to see if they are causing the draw?
My primary concern is the current draw. It's pretty excessive at idle.
Thanks!
Thank you. My probe is calibrated, so it's not that.
I saw in another post where you said they were 22k ohms... I was considering replacing them. What are these resistors for? Would the amp be ok to test shortly with them removed to see if they are causing the draw?
My primary concern is the current draw. It's pretty excessive at idle.
Thanks!
The RC network is likely used to damp high frequency noise that might appear on the rail-rail carrier waveform. The amp may work without them but monitor the waveform and be prepared to shut the amp down if the noise is excessive.
Perry with those resistors out I get no Gate switching...
The Pins on the resistors I marked as pin 2 in my photos of both resistors connect together and also connects to one of the pins of the daughter boards. I traced it and it goes to R144, a 7.5k resistor, and then to pin 5 of U105, a TL074C. Since this is the non-inverting input of an opamp, I traced pin 6 - it goes thru a 4.7k to pin 7, the output, so that's feedback. Pin 7 goes also to a 2.4k and then c142 and c143 and pin 13, so the inverting input of one of the other opamps... So these are more than noise limiting - they somehow are related to the output switching circuit.
It also only slightly reduces the current draw with them out. On another note, I started questioning the powersupply; maybe it was the issue after all. So the Gate and Drain outputs don't look real good... especially the gate... Looks same on both banks too. The Powersupply fets do start getting warm, but as it's 4 amps and at idle I sort of expect that. 3rd image here shows waveforms: Orion 1200D - Album on Imgur
The Pins on the resistors I marked as pin 2 in my photos of both resistors connect together and also connects to one of the pins of the daughter boards. I traced it and it goes to R144, a 7.5k resistor, and then to pin 5 of U105, a TL074C. Since this is the non-inverting input of an opamp, I traced pin 6 - it goes thru a 4.7k to pin 7, the output, so that's feedback. Pin 7 goes also to a 2.4k and then c142 and c143 and pin 13, so the inverting input of one of the other opamps... So these are more than noise limiting - they somehow are related to the output switching circuit.
It also only slightly reduces the current draw with them out. On another note, I started questioning the powersupply; maybe it was the issue after all. So the Gate and Drain outputs don't look real good... especially the gate... Looks same on both banks too. The Powersupply fets do start getting warm, but as it's 4 amps and at idle I sort of expect that. 3rd image here shows waveforms: Orion 1200D - Album on Imgur
If nothing else, it isolated the problem to the PS. Those resistors are used in the feedback circuit.
The amp is very similar to the JBL BP1200.1
The gate signal does look bad. Is that at the gate leg of the FET?
If so, what value gate resistors being used?
The amp is very similar to the JBL BP1200.1
The gate signal does look bad. Is that at the gate leg of the FET?
If so, what value gate resistors being used?
What does the signal look like on pins 9 and 10 of the 494?
What are the transistors Q8 and Q9 on the driver board?
Please post the images to this forum using the 'go advanced' and 'manage attachments' option.
When you post waveforms, set the scope to display them with so that they cover at least 3 major vertical divisions.
What are the transistors Q8 and Q9 on the driver board?
Please post the images to this forum using the 'go advanced' and 'manage attachments' option.
When you post waveforms, set the scope to display them with so that they cover at least 3 major vertical divisions.
TL494 pins 9 and 10 attached here and on the imgur link. Drivers are single C3198 transistors it looks like.
Attachments
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You need to set the scope to DC coupling and center the trace (no signal) on the center reference line.
Pins 9 and 10.
Pins 9 and 10.
Perry, It is at DC coupling and centered on the center ref line. Also the Drivers are a single C3198.
Yes, sorry those were pins 9 and 10 in the image, I labeled them wrong.
Yes, sorry those were pins 9 and 10 in the image, I labeled them wrong.
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Perry,
Sorry I misquoted the pins and also didn't have the scope grounded ::Oops
Here's the new image of the waveforms. I had to move the trace down to get a 3-div span like you wanted. The green indicator on the left indicates GND for the scope.
Sorry I misquoted the pins and also didn't have the scope grounded ::Oops
Here's the new image of the waveforms. I had to move the trace down to get a 3-div span like you wanted. The green indicator on the left indicates GND for the scope.
Attachments
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Pin 8/9 to 7 - 179 ohm (resister should be 220)
Drivers do not look replaced; amp doesn't look worked on ever before.
PSU Gate resistors are 22ohm
That circuit is similar in design, but values are different for most all components and there appear to be resistors in the drive circuit that are not in that schematic.
Drivers do not look replaced; amp doesn't look worked on ever before.
PSU Gate resistors are 22ohm
That circuit is similar in design, but values are different for most all components and there appear to be resistors in the drive circuit that are not in that schematic.
The overall design is what's important. I wasn't sure what it was using.
There are two 1k resistors mixed in with the gate resistors. They appear to be R733 and R734. You could try replacing them with a lower value (nothing lower than 220 ohms) to see if that helps.
There are two 1k resistors mixed in with the gate resistors. They appear to be R733 and R734. You could try replacing them with a lower value (nothing lower than 220 ohms) to see if that helps.
Perry,
Here's both banks Gate drive, on the Gate pin, overlayed. I suspect at the bottom where the waves overlap is potentially causing this issue because both fets are partly on at same time? I also did as you suggested and put lower resistors. Didn't seem to help any as I'm still pulling too much current.
Here's both banks Gate drive, on the Gate pin, overlayed. I suspect at the bottom where the waves overlap is potentially causing this issue because both fets are partly on at same time? I also did as you suggested and put lower resistors. Didn't seem to help any as I'm still pulling too much current.
Attachments
Didn't really help any as regards the current pull. And you see there wasn't really any change in the gate drive from the last screenshot.
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