This korean half bridge has me stumped a bit.
Previous owner states he purchased the amp, it was playing perfectly, and then suddenly shut down. Upon initial inspection the amp had been previously repaired and im guessing the repair tech incorrectly placed all the mosfet clamps between the fets and the sink!
Consequently ALL of the output fets are smoked and all have been removed. No solder bridges present after removal. Power supply fires up beautifully on 10v. Then the muting relays click off and the amp immediately shuts down (rail voltage is usually around 110v when this occurs).
I then inspected the 12v voltage regulation circuit which employs a pair of TA78t12. One was destroyed showing continuity across all pins. I removed both and measured voltage at the veirs. To my horror, full negative rail voltage was present on the input of the regs at powerup!
I do recall something about some amps using the negative rail voltage as a virtual ground so the 12v supplied to other components is stable. Is that the case here? Or should I not have negative rail voltage to the input of the 12v regs?
Thanks in advance.
Ps Im also having a difficult time finding a replacement for said voltage regulators. Origionals were a 3amp capacity in a to-220 case.
Previous owner states he purchased the amp, it was playing perfectly, and then suddenly shut down. Upon initial inspection the amp had been previously repaired and im guessing the repair tech incorrectly placed all the mosfet clamps between the fets and the sink!
Consequently ALL of the output fets are smoked and all have been removed. No solder bridges present after removal. Power supply fires up beautifully on 10v. Then the muting relays click off and the amp immediately shuts down (rail voltage is usually around 110v when this occurs).
I then inspected the 12v voltage regulation circuit which employs a pair of TA78t12. One was destroyed showing continuity across all pins. I removed both and measured voltage at the veirs. To my horror, full negative rail voltage was present on the input of the regs at powerup!
I do recall something about some amps using the negative rail voltage as a virtual ground so the 12v supplied to other components is stable. Is that the case here? Or should I not have negative rail voltage to the input of the 12v regs?
Thanks in advance.
Ps Im also having a difficult time finding a replacement for said voltage regulators. Origionals were a 3amp capacity in a to-220 case.
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Virtual ground isn't a term commonly used.
The driver ICs and the regulators are referenced to the negative rail. When measuring any voltages for these components, you need to place your black meter probe on the negative rail.
Do NOT connect any mains-powered scope ground (or any mains powered equipment ground) to the negative rail.
The driver ICs and the regulators are referenced to the negative rail. When measuring any voltages for these components, you need to place your black meter probe on the negative rail.
Do NOT connect any mains-powered scope ground (or any mains powered equipment ground) to the negative rail.
Thank you and roger that. I don't want the oscilliscope to explode in my face......LOL!!
Any ideas on where i should start looking to ascertain why the amp keeps shutting down when it tries to power up the output section?
As I understand it, this type of amp should power up without the output fets in place and the low side should oscillate?
I was thinking that i should remove the driver board and see if the problem remains at power up in an attempt to isolate the problem?
Any ideas on where i should start looking to ascertain why the amp keeps shutting down when it tries to power up the output section?
As I understand it, this type of amp should power up without the output fets in place and the low side should oscillate?
I was thinking that i should remove the driver board and see if the problem remains at power up in an attempt to isolate the problem?
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Yes, I have full negative rail voltage on all sides of all filter inductors. (Ground probe is on negative power terminal.)
When the relays do engage for a moment I'm also seeing a LARGE dc offset on the channels.
When the relays do engage for a moment I'm also seeing a LARGE dc offset on the channels.
The relays engaging is driving the DC to the protection circuit which is shutting the amp down, most likely.
Do you have a 120v incandescent lamp that you could touch to the rail voltage on the inductors to see how much current the source can supply?
The short could be direct, or just through a resistor. The lamp would help determine what the problem is likely to be.
Do you have a 120v incandescent lamp that you could touch to the rail voltage on the inductors to see how much current the source can supply?
The short could be direct, or just through a resistor. The lamp would help determine what the problem is likely to be.
Ok I just just tried that and the amp refused to power up at all.
Removed lamp, allowed to power up and touched lead to complete the circuit and something in the preamp section popped and let loose a whisp of smoke.
I cant see anything on visual inspection from were that whisp of smoke origionated from...
I did however connect the incandescent across the speaker terminals and powered it up. Light bulb lights up really really well until the relays open again. Ugh.
How often will these amps take out the enormous capacitors (1200microFarad, 200v)? Of the 20 caps of this size only 7 behave normally when tested for continuity accorss their terminals.
How often will these amps take out the enormous capacitors (1200microFarad, 200v)? Of the 20 caps of this size only 7 behave normally when tested for continuity accorss their terminals.
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Do you possibly have an inductor shorted to a trace on the board?
You stated that you had no solder bridges so that aren't many possibilities that can light up the lamp.
You stated that you had no solder bridges so that aren't many possibilities that can light up the lamp.
Small solder bridge found and fixed but problem persists, I think.
I've removed all 4 main torroid inductors as well is the 2 iron core inductors. All look perfect no bare areas on the board under them.
An externally hosted image should be here but it was not working when we last tested it.
Obviously with the inductors removed there is no DC being sent to the speaker leads to then send the amp into protect. However I am still getting a -142 vdc on the inputs of all 4 main inductors. (Refrenced to both terminal ground and speaker ground.) That cant be right.
I can see where someone attempted a repair on the rectifiers....and there is 1 non oem rectifier in place. However all 4 have the same exact output, one leg 125v, one leg -125, and middle leg has the switching drive being fed to it.
What are your thoughts at this point?
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In the picture above with the removed inductors, on the bottom left 3 spots for the output mosfets....ALL legs have rail voltage.
Measure the resistance across the pads for the individual the individual transistors for that group. Do you see any difference between the 3 transistors?
Measure Leg 1-2, 1-3 and 2-3.
Measure Leg 1-2, 1-3 and 2-3.
Ok Leg 1-2 starts at about 12,000 ohms and starts climbing. After about 3 minutes of waiting, it is at 32,000 and continuing to climb very very slowly. Leg 2-3 starts at about 33,000 and starts climbing after about 2 minutes it is at 60,000 and climibing more slowly.
1-3 is a stable 33,300 ohms right off of the bat.
1-3 is a stable 33,300 ohms right off of the bat.
None of that is a direct short or even anything that could light up a light bulb. Do you think that you may have had a more serious problem or that this one has changed to something than the direct short that you had earlier?
Install a jumper wire in the place of the inductor for the conductive group of outputs and see if it will still light the lamp.
Or connect the lamp to whatever ground you were using and touch the other terminal of it to the transistor side of the inductor.
Or connect the lamp to whatever ground you were using and touch the other terminal of it to the transistor side of the inductor.
EDIT: I just now saw your post and will do so just to make sure the problem is alleviated.
Ok between troubleshooting my car's AC and taking my son to therapy, I pulled the audio driver board just to see what happens. Problem resolved. I am quite confused how voltage was getting to the drain pad of all 4 internap amps but it appears *knock on wood* to be gone.
Now comes troubleshooting the audio card time....lol
Ok between troubleshooting my car's AC and taking my son to therapy, I pulled the audio driver board just to see what happens. Problem resolved. I am quite confused how voltage was getting to the drain pad of all 4 internap amps but it appears *knock on wood* to be gone.
Now comes troubleshooting the audio card time....lol
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Yes zero voltage on the drain pad of the fets with the audio card removed. Double checked with incandescent bulb and indeed no DC found.
But how would the driver card send rail voltage to the gate pads and the drain pads though? I am quite confused there....
But how would the driver card send rail voltage to the gate pads and the drain pads though? I am quite confused there....