I ran into one of these with a blown up power supply, but the outputs were fine.
Replaced all transistors/resistors in the power supply circuit. Found an open R515 in the output stage for some reason, so i replaced that.
Now it works, plays with sound. But the amp idles at almost 3 amps and the toroid is getting really hot really fast.
Checked the drive signals going to the FETs and they are perfect. Also the outputs/power supply MOSFETS i left unclamped, and they are all getting just luke warm to the touch.
any ideas?
Replaced all transistors/resistors in the power supply circuit. Found an open R515 in the output stage for some reason, so i replaced that.
Now it works, plays with sound. But the amp idles at almost 3 amps and the toroid is getting really hot really fast.
Checked the drive signals going to the FETs and they are perfect. Also the outputs/power supply MOSFETS i left unclamped, and they are all getting just luke warm to the touch.
any ideas?
Ring-testing toroids in car amps is VERY unreliable. When removing it, you will move the windings enough to open any shorted windings and it will appear to be OK. It's likely OK if it's not drawing excessive current (30+ amps). Ring testing is really only reliable for transformers that have fixed terminals or those potted in epoxy.
Yea, it runs fine but its pulling about 3 amps idle. and the toroid starts overheating almost instantly, almost like the core is going into saturation. BUT the MOSFETs dont get hot.
Well, Another thing I noticed is even with the low pass filter turned off so the amp is running all-pass, it still sounds like lowpass with almost no highs. just less sharp on the true low pass. Ill check the frequency when I get back to the shop. The person who previously owned this amp, bought it new and purposely blew it up running full volume into 1 ohm load. Did it on purpose to see how long it would take to blow up. Idiots.
Well, Another thing I noticed is even with the low pass filter turned off so the amp is running all-pass, it still sounds like lowpass with almost no highs. just less sharp on the true low pass. Ill check the frequency when I get back to the shop. The person who previously owned this amp, bought it new and purposely blew it up running full volume into 1 ohm load. Did it on purpose to see how long it would take to blow up. Idiots.
When ring testing a toroid you should not remove it, always test in circuit. As Perry said you may "correct" the shorted turns and it will test good.
You never stated the frequency you measured.
The outputs may have a marginal problem. There are only 4 of them, replaced them to eliminate them as a possible cause for your high idle current. If you have a good transistor tester compare the current gains (HFE) between the MOSFETS you remove with each other.
You never stated the frequency you measured.
The outputs may have a marginal problem. There are only 4 of them, replaced them to eliminate them as a possible cause for your high idle current. If you have a good transistor tester compare the current gains (HFE) between the MOSFETS you remove with each other.
I use the blue ring tester made by Ana Tek. It has a wide range testing range for the Q of a coil or transformer. It has a vertical row of 8 LEDS on its side that indicate the level of Q of the coil or xformer has. The more LEDS lit going up the side the higher level Q The top 3 LEDS are green to indicate good, below that are 2 yellow LEDS that indicate questionable, then 2 red LEDS to indicate bad. If no LEDS light then the coil or xformer has a direct short across it ( no rings).
I'm familiar with the snubber on the xformer primary side skewing the readings. My experience so far in using the ringer on the primary side with snubbers has been the yellow LEDS light. If I still really suspect the xformer I could lift a lead on the snubber resistor or cap to get it out of circuit and recheck it. I have yet to do that. Those that test in the yellow range but are good I make a note of it for that make and model of amp for future reference. The ringer does have a limitation in that regard but if you adjust for that it is not a issue.
I will not say with 100% confidence that every coil , inductor or xformer that tests bad ( ex a inductor with only 10 turns) with the ringer truly is bad in all cases but I can say with 100% confidence that every coil or xformer that tests good is. So even if the ringer was only useful in knowing if a coil or xformer was truly good it is well worth the $60.00 investment to have on a tech's bench.
You ought to take a look at it Perry, for $60 (about a tank of gas) it can save a lot of bench time. They also sell it in kit form for less. Link is below.
Ana Tek Corporation
I'm familiar with the snubber on the xformer primary side skewing the readings. My experience so far in using the ringer on the primary side with snubbers has been the yellow LEDS light. If I still really suspect the xformer I could lift a lead on the snubber resistor or cap to get it out of circuit and recheck it. I have yet to do that. Those that test in the yellow range but are good I make a note of it for that make and model of amp for future reference. The ringer does have a limitation in that regard but if you adjust for that it is not a issue.
I will not say with 100% confidence that every coil , inductor or xformer that tests bad ( ex a inductor with only 10 turns) with the ringer truly is bad in all cases but I can say with 100% confidence that every coil or xformer that tests good is. So even if the ringer was only useful in knowing if a coil or xformer was truly good it is well worth the $60.00 investment to have on a tech's bench.
You ought to take a look at it Perry, for $60 (about a tank of gas) it can save a lot of bench time. They also sell it in kit form for less. Link is below.
Ana Tek Corporation
#9:
Did the transformer show any signs of overheating?
Could you tell if the core was cracked?
#8:
I don't want people to go out and buy equipment that they don't need. I've been doing this for more than 25 years and I can tell you that I've never found a use for a ringer in car amps except for checking transformers or inductors with fixed terminals or those that were potted. In all that time, I've found only about 10 that were defective. Most showed signs that they overheated so they were obviously defective. When I repaired TVs, the ringers that I have were used regularly. That's simply not the case with car amps. If someone already has a good scope and a good multimeter (or two) and they want a ringer they can buy a ringer but they shouldn't all of a sudden expect it to make their life easier.
Did the transformer show any signs of overheating?
Could you tell if the core was cracked?
#8:
I don't want people to go out and buy equipment that they don't need. I've been doing this for more than 25 years and I can tell you that I've never found a use for a ringer in car amps except for checking transformers or inductors with fixed terminals or those that were potted. In all that time, I've found only about 10 that were defective. Most showed signs that they overheated so they were obviously defective. When I repaired TVs, the ringers that I have were used regularly. That's simply not the case with car amps. If someone already has a good scope and a good multimeter (or two) and they want a ringer they can buy a ringer but they shouldn't all of a sudden expect it to make their life easier.
Thats the funny thing perry, It didnt show signs of either. And bending/twisting didnt do any difference.
But swapping the transformer, worked fine. I didnt unwind the old one to see the issue, only thing that could have occured is maybe a short to the core, or cracked core. Hard to say.
However, the guy PURPOSELY beat the thing wide open on 1 ohm and let it roll the smoke out on purpose. So, anything is possible....
But swapping the transformer, worked fine. I didnt unwind the old one to see the issue, only thing that could have occured is maybe a short to the core, or cracked core. Hard to say.
However, the guy PURPOSELY beat the thing wide open on 1 ohm and let it roll the smoke out on purpose. So, anything is possible....
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