I've found that those opto-couplers could seem perfectly OK (checking with a meter or at low frequencies) but when the amp begins to oscillate, they cause the amp to draw excessive current. Of course, if they appear shorted with an ohm meter, they're defective.
Having the drive signal present on the gates isn't always a reliable indicator. Sometimes the opto-couplers are damaged but still work at low frequencies. They only cause problems when the amp begins to oscillate.
Question does the circuit oscillate naturally with no signal input
Question does the circuit oscillate naturally with no signal input
No. The gate drive signal you'll see when it's driven with a signal won't be oscillation either. It's simply a distorted version (badly clipped) of the input signal.
From my experience, yes.
You should be able to edit posts. If you can't currently edit posts, you should be able to do so relatively soon.
You should be able to edit posts. If you can't currently edit posts, you should be able to do so relatively soon.
Removed output Fets left bank fet245,246,247,248,249 and right bank fet255,256,257258,259 and rechecked. Checked vgs voltages after checking gate fet resistors 5 ohm in both banks of gate resistors. I also checked R360 and R361 under shunt resistor R282 and measured 1/2 of 320ohms as you said it be because they are in parallel and re soldered them. The left bank vgs voltage was 18 volts and right bank was vgs 0 volts even after the new opto-couplers were installed. With no input signal and the left opto_couplers pins 5 & 8 was 20 volts and on the left one 14 volts . Also remove and checked fet327, Q343 fet 470 471 fet435,436,437,438,439,440,441,442,443,444 D446,447,448,448. all checked good and reinstalled the power supply parts. the power supply measures 149 volts and scoped it with no ripple on the DC voltage. with the out puts out and 261 that has a Vgs voltage of 46volts. Also Fet327 vgs is 0volts. I also changed the op amp IC between the 2 electronlitica in the drive signal ic you told me I should see a signal if I drove a signal on pin 1 & 5 of NE5532 no change in signal coming in and the same voltage on the opto couplers and the output banks vgs voltages. when ouputs are in I get 149 volts dc on my speaker outputs and no signal and bias gain pot full counter clockwise and the protection kicks in and then comes back on and then the protection cuts in over and over again same as before. Where can I go from here Perry?
I hope this make sense and not to much to take in in one mass posting
I hope this make sense and not to much to take in in one mass posting
What is the purpose ( what do they do) of fet327 and261? Just curious as I try to understand how these circuit works. For the next one.
If I'm not mistaken, FET261 is a 15v regulator (15v above the negative rail). FET327 is used to drain the rail caps when the amp is powered down.
Try shorting pins 6 and 7 of the 5532. Does that produce a drive signal on the gates of the FETs?
Try shorting pins 6 and 7 of the 5532. Does that produce a drive signal on the gates of the FETs?
with pin 6&7 shorted I get left outputs bank go from vgs from 18 volts to 0 volts and right bank stayed at vgs 0 volts.🙂
In reference when you take the gate signals where do you clip your ground on your scope probe to check the signals on the gates? No idea what the amplitude volts per division on display I should be looking for the signal on the gates.
are we going in the right direction now with our output fets vgs voltages are sitting at 0 volts?
left opto- coupler on pins 5&8 is 22 volts and right opt-coupler is 14.6 volts with pins 6&7 shorted on the ic also
In reference when you take the gate signals where do you clip your ground on your scope probe to check the signals on the gates? No idea what the amplitude volts per division on display I should be looking for the signal on the gates.
are we going in the right direction now with our output fets vgs voltages are sitting at 0 volts?
left opto- coupler on pins 5&8 is 22 volts and right opt-coupler is 14.6 volts with pins 6&7 shorted on the ic also
Do you have any signal on 6 and 7 when you drive a signal into the amp?
It's probably best to ground the scope to the amp ground for now. One gate signal will be referenced to the negative rail. The other is floating.
The amplitude will be about the same as the voltage across the opto-coupler (pins 5 and 8).
It's probably best to ground the scope to the amp ground for now. One gate signal will be referenced to the negative rail. The other is floating.
The amplitude will be about the same as the voltage across the opto-coupler (pins 5 and 8).
No signal at pin 6&7 with a drive signal into the amp. I can scope it up to the IC right before the IC you wanted me to check between the 2 electrolytic capacitors. I have a chopper carrier with the audio riding on top of the chopper carrier wave at the output of that IC pin 1 &7 and then it is gone can't find it anywhere else on the board in that area after that and not on pins 1&7 of the one between the caps that you wanted me to check if it is suppose to be on pin 1 or any of its input pins on that IC or any components around that area either
Hi Perry i used the quick post last night and never used it before and I don't know id it send you a email of my posting or not. I don't want to be a annoying but just not sure if it did or not with quick post?
For some reason the email notifications for this thread haven't been sent to my email so I didn't realize that there were any other posts in it. I have the PMs turned off on the forum.
I think there should definitely be audio on pin 1 of the IC between the caps. Do you have audio on pin 3 of that op-amp? If not follow the circuit back to see what feeds pin 3. I think it goes through one of the 100uf caps near the op-amp. If you don't have it there, follow the circuit back until you find signal.
I think there should definitely be audio on pin 1 of the IC between the caps. Do you have audio on pin 3 of that op-amp? If not follow the circuit back to see what feeds pin 3. I think it goes through one of the 100uf caps near the op-amp. If you don't have it there, follow the circuit back until you find signal.
Perry I brought the amp over to my main bench to hook it up from sitting on the shelf as i had 2 big car amps to do and a larger 250 rms per channels House deck and a high-power car deck (JVC KD-R900 used for sound competitions they are running a 6500 watt amp with it with Kicker subs and have won 2 years in a row) to put parts in and get back to the costumers and low and behold when I hooked the xtant back on on my 5 amp supply with the outputs still out to trace that signal the power led lit and the other 2 that normally come on but the protectection led wont fire up checked all the voltages you gave me in the past and the jfet is not clamping shut to bring the light on so I got no power to my low power circuits either the peamps and phaseamp ic amps I checked the circuits could find no problems even repulled the couplers and changed the ic between the eltrolytics and checked the small transitor and Jfet beside each other all good. The led is good as it fires up with no power and put the dvm in diode checker mode across emitter and base of that transistor by the jfet and the led fires up. checked all components to elinate any diode and transistor and caps all good I am at a loss at what happened from putting it away and taking it back out and now npt powering up I have my 149 volts dc on the 2 heavy shunt resistors the output coupler are the same voltages as the other night on the outputs. What could have happened ? and what can I do to find out what is wrong so I can finish my lost signal tracing and get it out of the shop. I never had an amp so temper-mental before. also resoldered all the compenets in that are thing a solder joint may have cracked on the surface mount components in that section from the board flex or something from pick it up and moving it from shelf to bench several times no luck. Also the fans are run on low speed they not running very low voltages on them.
The jfet is switched off at the same time that the LED is switched on. The FET clamps the input to the opto-couplers during/for muting.
Which LEDs are lit?
Which LEDs are lit?
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