I swapped the inductors and, surprise, the negative went down.
Now, with the VR951 all the way down, the voltages are +25,5V and -34,4V.
If I increase the positive to the expected working voltage of +30 the negative goes up to 39.
Now the gap is "only" 9V and the negative voltage is influenced by the VR951.
@Eva - I tried to send the PDF but it bounced back. I'l try again later in the morning.
Pictures will come shortly.
Now, with the VR951 all the way down, the voltages are +25,5V and -34,4V.
If I increase the positive to the expected working voltage of +30 the negative goes up to 39.
Now the gap is "only" 9V and the negative voltage is influenced by the VR951.
@Eva - I tried to send the PDF but it bounced back. I'l try again later in the morning.
Pictures will come shortly.
I have taken the inductors from another 922 amp and applied the 47 Ohm/10W load to both rails.
+34,3v and -34,4V
Much better
I measured all the 4 inductors (2 of this amp and 2 of the twin one) with an LC meter and they all read the same value - can not understand it
but as long as it works, is OK.
I know it's not of much help however the pin 9&10 voltage of the IC951 is now 3.84V, in line with the other working amp.
The bad news is that the VR951 is all the way down so I can not reduce the voltage to the desired 30V - something is still not 100% OK but way better than before. I think I'll re-mount the Sanken and see if it improves.
+34,3v and -34,4V
Much better
I measured all the 4 inductors (2 of this amp and 2 of the twin one) with an LC meter and they all read the same value - can not understand it
but as long as it works, is OK.I know it's not of much help however the pin 9&10 voltage of the IC951 is now 3.84V, in line with the other working amp.
The bad news is that the VR951 is all the way down so I can not reduce the voltage to the desired 30V - something is still not 100% OK but way better than before. I think I'll re-mount the Sanken and see if it improves.
If it's regulated, it would regulate it with or without the inductors.
It's likely that the negative half of the regulator isn't working properly. If Q953 isn't conducting, it's allowing R967 to pull the voltage on pin 16 down which would tend to make the regulated voltage higher than it should be. I'm assuming that the pot should be relatively close to the mid point when the rail voltage is 35v.
The service manual states that the rail voltage is supposed to be ±35v.
It's likely that the negative half of the regulator isn't working properly. If Q953 isn't conducting, it's allowing R967 to pull the voltage on pin 16 down which would tend to make the regulated voltage higher than it should be. I'm assuming that the pot should be relatively close to the mid point when the rail voltage is 35v.
The service manual states that the rail voltage is supposed to be ±35v.
Right it's +/- 35V. I had in mind 30V - don't know why
I'll have a look to the section you highlighted in the green square later.
Eva - the inductors are 0,135 mH (more or less). I like the brute force solution
The regulation control loop is compensated to be stable with the inductors in place (with a zero very close to LC filter resonance to provide some phase margin, see RC network before the pot). Removing the inductors moves the LC resonance to a much higher frequency (L changes from 135uH to a few uH from transformer leakage inductance) and is likely to cause oscillation, which may be fatal under load. Also, that kind of inductor-less regulation results in high stress on the push pull MOSFET, rectifiers and +B capacitors, and high EMI, I have analyzed it in detail on Alpine amplifiers.
Both rails are linked by duty cycle, they can't be regulated separately. The only way to get very dissimilar rail voltages on that SMPS topology is a faulty output inductor or capacitor, or a strongly unbalanced load. That's how I figured out that the inductors were the problem.
The feedback circuit just regulates the highest of the rails (at the expense of not controlling the other) but not in the same proportion, my math tells that the negative rail should be limited around 35V (R902) while the limit for the positive one is adjustable from 21V to 38V (VR951).
If it's not working that way, you should check all the feedback components (stuff around the green square) as Perry suggested. There may be an open resistor or solder joint on the negative rail sensing (plus the inductor problem).
Both rails are linked by duty cycle, they can't be regulated separately. The only way to get very dissimilar rail voltages on that SMPS topology is a faulty output inductor or capacitor, or a strongly unbalanced load. That's how I figured out that the inductors were the problem.
The feedback circuit just regulates the highest of the rails (at the expense of not controlling the other) but not in the same proportion, my math tells that the negative rail should be limited around 35V (R902) while the limit for the positive one is adjustable from 21V to 38V (VR951).
If it's not working that way, you should check all the feedback components (stuff around the green square) as Perry suggested. There may be an open resistor or solder joint on the negative rail sensing (plus the inductor problem).
There are many millions of power supplies that don't have inductors before the capacitors. I understand that it could change the stability under some conditions, it's not going to cause problems at idle. In most amps (including this one, I believe), jumping the inductor is OK for troubleshooting a problem like the one he had.
Yes, inductors can reduce the stress on power supply components but at idle, it's not a concern.
Yes, inductors can reduce the stress on power supply components but at idle, it's not a concern.
In power supplies without output inductors the turns ratio of the transformer is substantially lower. In this power supply, due to the high turns ratio, something like 15-20V would be applied to transformer leakage inductance during on time, resulting in very high di/dt and EMI.
Imagine over 100A/us current slope on the primary side... Not healthy...
Imagine over 100A/us current slope on the primary side... Not healthy...
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The only thing I'd like to clarify is that jumping the inductors is not unsafe (especially on this type of power supply) and is not likely to cause any damage when testing.
I did this with several amps I have here. I shorted one inductor (when there were 2 individual inductors), both inductors and 1 or both halves of a common mode inductor. None had any problem that would cause any damage.
In PPI amps and some other amps, they use very large inductor cores. They tend to drop voltage (peak voltage from transformer, minus ringing, is significantly greater than the rail voltage at idle). These operate differently than most amp power supplies, in this regard. I jumped the PPI and the rail voltage was within 0.1v of the voltage without the jumpers. In an amp with this type of inductor and an un-regulated supply, the rail voltage would have increased if it were jumped.
The other amps that were tested used a much smaller common mode inductor or that had 2 individual inductors, the rail voltage was within ~1/2 volt of the peak voltage on the transformer's secondary both before and after the jumpers were connected. The jumpers made essentially no difference in the rail voltage.
In the amp with individual inductors, I shorted between adjacent windings, the regulation held and both rails remained equal.
Manina, I think you should try installing the inductor you pulled from this amp in the other pioneer amp to see if it produces the same results.
If you're concerned that the inductor is shorted or has worn insulation where the windings overlap, you can check it with your meter. Touch one probe to the tinned end of the inductor. Take the other probe and rub it over the area where you suspect that the insulation is worn through. The meter should never change from OL (assuming that it reads OL with open leads). The most likely place for it to short is the point where the terminal winding first meets the rest of the windings.
I did this with several amps I have here. I shorted one inductor (when there were 2 individual inductors), both inductors and 1 or both halves of a common mode inductor. None had any problem that would cause any damage.
In PPI amps and some other amps, they use very large inductor cores. They tend to drop voltage (peak voltage from transformer, minus ringing, is significantly greater than the rail voltage at idle). These operate differently than most amp power supplies, in this regard. I jumped the PPI and the rail voltage was within 0.1v of the voltage without the jumpers. In an amp with this type of inductor and an un-regulated supply, the rail voltage would have increased if it were jumped.
The other amps that were tested used a much smaller common mode inductor or that had 2 individual inductors, the rail voltage was within ~1/2 volt of the peak voltage on the transformer's secondary both before and after the jumpers were connected. The jumpers made essentially no difference in the rail voltage.
In the amp with individual inductors, I shorted between adjacent windings, the regulation held and both rails remained equal.
Manina, I think you should try installing the inductor you pulled from this amp in the other pioneer amp to see if it produces the same results.
If you're concerned that the inductor is shorted or has worn insulation where the windings overlap, you can check it with your meter. Touch one probe to the tinned end of the inductor. Take the other probe and rub it over the area where you suspect that the insulation is worn through. The meter should never change from OL (assuming that it reads OL with open leads). The most likely place for it to short is the point where the terminal winding first meets the rest of the windings.
In the W.E. I have checked the section Perry circled (well, squared) and all is OK.
I mounted the inductors I'm sure are OK and the finals. Voltage is OK. It's stable in the 35V for both rails. I'll check the other two inductors before placing them in the other amp that I use as spare.
I'll now change the rail caps and place new ones as, at least, one of the old is gone (it was on the negative rail).
Is it safe to use 35V caps (as the stock ones) or shall I upgrade to 50v? I have anyway to change them and, giving the operating voltage of the amp, the stock ones are borderline (IMHO)
Unfortunately, I have to wait for the IRFIZ44N as it takes some time to get them here (local shop run out easily) then the amp should be fully operational.
I have some IRFI 3205PBF in house - is it safe to use them or it's likely to oscillate?
I mounted the inductors I'm sure are OK and the finals. Voltage is OK. It's stable in the 35V for both rails. I'll check the other two inductors before placing them in the other amp that I use as spare.
I'll now change the rail caps and place new ones as, at least, one of the old is gone (it was on the negative rail).
Is it safe to use 35V caps (as the stock ones) or shall I upgrade to 50v? I have anyway to change them and, giving the operating voltage of the amp, the stock ones are borderline (IMHO)
Unfortunately, I have to wait for the IRFIZ44N as it takes some time to get them here (local shop run out easily) then the amp should be fully operational.
I have some IRFI 3205PBF in house - is it safe to use them or it's likely to oscillate?
The drive circuit looks like it should be able to drive the 3205s. You may have to reduce the value of R978 and R979 to 1k or just a bit lower. If you power it up and the FETs run hot at idle and isn't drawing excessive current, change those resistors.
If you only have 35v rails, you don't need 50v caps. Unless you can find 3300uf caps rated for 50v that will fit, go back with the original 3300@35. 35v caps will operate at 35v with no problems.
If you only have 35v rails, you don't need 50v caps. Unless you can find 3300uf caps rated for 50v that will fit, go back with the original 3300@35. 35v caps will operate at 35v with no problems.
I placed the inductors in the working amp and I can confirm they were the cause of the problems.
With them in place, I ether get high voltage or the led blinks and the amp does not power up properly. I'll rewind both of them to be on the safe side.
As I have anyway ordered the 44n, I'll wait for them rather then to use the 3205 - just to be on the safe side.
So far, I think the amp is fixed.
Thanks for all your help.
With them in place, I ether get high voltage or the led blinks and the amp does not power up properly. I'll rewind both of them to be on the safe side.
As I have anyway ordered the 44n, I'll wait for them rather then to use the 3205 - just to be on the safe side.
So far, I think the amp is fixed.
Thanks for all your help.
After some time without any problem, I'm having (new) issues with this amp but, now, in the output section - to be precise in the right channel.
Each channel has 2 pairs of Sanken (2SA1673 and 2SC4388) - in the right channel one of the 4388 gets very hot after few seconds of operation.
The amp start producing sounds without any distortion as far as I can hear (I haven't a scope) with a current draw of around 1A - after 20-30 seconds, the draw start to increase. The more hot the 4388 become, the higher the draw. Then the draw increase drammatically and I disconned everything to avoid further issues.
I have tested the 4 transistor with the meter and they seems OK. I tried to exchange the position (moving one pair to the postion of the other pair and viceversa) and the 4388 that become hot is in the same position (even if is the exchanged one) - Q266.
With only 1 pair installed, no matter in which slot (Q265/266 or Q268/269) or which pair of the tranisitor, the temperature and the draw is OK. I also tried to swap the transistor of the pairs but with the same result.
Only when all 4 are installed, the temperature of 1 4388 (always in the same position Q266) goes high.
Any suggestion?
Each channel has 2 pairs of Sanken (2SA1673 and 2SC4388) - in the right channel one of the 4388 gets very hot after few seconds of operation.
The amp start producing sounds without any distortion as far as I can hear (I haven't a scope) with a current draw of around 1A - after 20-30 seconds, the draw start to increase. The more hot the 4388 become, the higher the draw. Then the draw increase drammatically and I disconned everything to avoid further issues.
I have tested the 4 transistor with the meter and they seems OK. I tried to exchange the position (moving one pair to the postion of the other pair and viceversa) and the 4388 that become hot is in the same position (even if is the exchanged one) - Q266.
With only 1 pair installed, no matter in which slot (Q265/266 or Q268/269) or which pair of the tranisitor, the temperature and the draw is OK. I also tried to swap the transistor of the pairs but with the same result.
Only when all 4 are installed, the temperature of 1 4388 (always in the same position Q266) goes high.
Any suggestion?
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