Hello ! I am working on fixing a blown salt 8 amplifier it looks as though one of the output fets died and took the output section along with the power section with it. I have repaired a few amps before but am no way an expert but do have the desire to learn more and get better at amp repairs. Ive established that the power section mosfets are IRF7530's but I do not know what the driver NPN/PNP transistors are, also the output section uses 24N40F's I was wondering would it be possible/ worth it to replace them with 24N50F's so the amp can handle charging in the 15v range a bit better ? From my understanding these SALT amps run very close to the output fet breakdown voltage when charging above 14.4-14.8 which leads to issues sometimes when charging any higher. Also what are the 5pin output driver chips there seems to be 4 of them directly in from of the driver card, rumor is they are all TC4452's but I just wanted to confirm. If these are blown is there a high chance it took the driver card with it as well? Any help would be greatly appreciated, I may ask alot of questions but I am trying to learn for future projects.
Your research seems to be right.
Are the PS drivers defaced?
The driver board has a fair chance of surviving due to the 4452 drivers but you'll have to test for drive signal before connecting it to unlimited power.
Are the PS drivers defaced?
The driver board has a fair chance of surviving due to the 4452 drivers but you'll have to test for drive signal before connecting it to unlimited power.
Thank you for the reply! I originally thought they were charred but I was able to clean them off enough to identify the model. Do you think its worth swapping out the 24n40f's for the 24n50f's (i see they have a fair amount more of input capacitance) ? I am trying to figure out what the rail voltage would've been so I can have a fair amount of headroom when charging the amp at 15.5v.
I don't know enough about the amp to know if the extra capacitance will be a problem. From the information I have, the 20N50F is used in some similar amps. Maybe someone here will have tried the 24N50F enough times to know if it's a reliable sub.
Fair enough ! Do you know of a readily available substitute for the B631k/D600k Transistor combo, this seems to be the driver transistors for the PS. None seem blown but its best to replace them. And I noticed a capacitor was charred and deformed but I do not know how to located a replacement, the capacitor closest to it reads 223j100. I'll include pictures, again thank you so much for your assistance.
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Best to replace perfectly good parts? It's unlike that you will find exact replacements. Are you going to replace all of them? The BD139 and BD140 are typically used as PS driver replacements.
The cap value you gave is a 22000pF or 22nF 100v ±5% film cap. I have C275 as being 33000pf. You can confirm by seeing if it's in series with the 1k resistor R275. Whatever the value, find one that fits the allotted space.
The cap above may be undamaged (electrically). If so, you could measure the value to confirm that it's 33000pF.
The cap value you gave is a 22000pF or 22nF 100v ±5% film cap. I have C275 as being 33000pf. You can confirm by seeing if it's in series with the 1k resistor R275. Whatever the value, find one that fits the allotted space.
The cap above may be undamaged (electrically). If so, you could measure the value to confirm that it's 33000pF.
Thanks Perry, you are right if they are good no need to be replaced, I just wasn't sure if they would be weakened or compromised due to how dramatically the the power section failed. after I confirm there are no shorts i'll power it up and test the drive signal on the gate to confirm if they are okay or not. Thank you for the replacement recommendation, I was going to replace them all but if there is not short between the emitter collector or base I'll leave it as is. I removed the cap from the circuit and confirmed it still reads 33000pf, if I run into any further issues I will report back, Many thanks ! 🙂
When trying to determine if the drive signal is good at the gate pads of the PS FETs, remember that, without the loading capacitor, you won't be able to see if there is a marginal drive from the driver transistors. A weak driver signal may look OK with only the scope loading the signal.
Thank you for the input ultra, in that case I may stick with the stock 24N50's. May I ask what amplifier you used them on ?
Thanks Perry, I will test when I get home from work. If i remember correctly you recommend loading it with a .01uf ceramic cap between gate and source.
That value will work. Ceramic will work. I use film capacitors but there won't be any difference for this testing.
On flextron amps, just like yours. I had some results with zenon amps though
I believe mouser or digikey had a bad batch of 24n50's a while back. I got a 15 out of 50 would read as igbt's in my tester but the ones that read normal worked without issue for me in 2 dd amps with that circuit. Also In my experience those amps take around 15 amps to power up when u get to that point.
Thanks for all the input very much appreciated, I've examined the output section and cant find any shorts on the drivers once the blown fets were removed so I (THINK) they're okay. I did have a few questions if anyone could answer.
1. Is it strange only one side went down? I know from looking at the inductors that its essentially 2 separate amps paralleled at the output.
2.Is this output section setup in 4 bank of fets, where 12 fets are high side and 12 are low but split into 4 banks 2 for each half of the amp. (just confirming)
1. Is it strange only one side went down? I know from looking at the inductors that its essentially 2 separate amps paralleled at the output.
2.Is this output section setup in 4 bank of fets, where 12 fets are high side and 12 are low but split into 4 banks 2 for each half of the amp. (just confirming)
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1.I have had many times class D amps with only one side/amp being affected.
2. Yes. 6 high, 6 low per side/amp.
2. Yes. 6 high, 6 low per side/amp.
You typically have a single output FET fail, initially. When that happens, that alone can cause the amp to go into protection but it generally causes a second FET to fail (generally one on the opposite half of the same group (side) of outputs) and if the amp doesn't go into protection (as it should have when the first FET failed) and the fuse doesn't blow (common for it not to blow with large amps) the power supply fails.