ok, next dumb question. the 2 pins, your referring back to the preamp ribbon plug? And what is in that circuit, just the TL072 before you get to the preamp? if so ill just swap out the TL072 as its likely damaged. and earlier you mentioned the supply resistors to the preamp board, are these resistors your referring to, on the actual preamp board itself? or are they on the power amp board, as i never tested any on the power amp board except in the regulator areas and etc...
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The '2 pins' were the ones in the black plug where you have the jumpers.
If I'm not mistaken, you should read ~0 ohms from pins 1 and 7 of the RCA op-amp to those pins in the black header. You should have clean audio on both of of those pins in the header. Remove the jumpers so nothing can interfere with the signal from the RCA op-amp.
If I'm not mistaken, you should read ~0 ohms from pins 1 and 7 of the RCA op-amp to those pins in the black header. You should have clean audio on both of of those pins in the header. Remove the jumpers so nothing can interfere with the signal from the RCA op-amp.
ok. I am going to head back to the shop to work on a couple of xbox360s, and ill drag that blasted thing back to the bench and see what it does. but i bet the TL072 is bad, especially if it gets its power from those regulators. as those suckers blew TWICE. once before i had the amp, and once when i had the amp. so hehe.....
yea they had to be good becuase i had a positive and negative 15V sitting at the TL072.
Also, I scoped everything out. it was baaad..... real bad... the noise was definitely comming from the op-amp. for sure. Posted below are the recordings for the DSO-5200 but i need to figure out how to convert it into movie format, not sure how to do it. maybe ill just upload one frame of it.
After replacing the TL072 the noise and motorboating went away, and i had pretty loud audio. unfortunately, it was distorted even at low volume. Not distorted as if it were clipped off on one of the rails, that has a distinct distortion.
This one had almost like an overdrive style of distortion. But unfortuantely didnt didnt go away even at low volume from the MP3 player. it could be caused from the player, im not sure yet. however, i do have sound. its not the strongest in the world, but i do have sound now. even though it is totally distorted.
Also, I scoped everything out. it was baaad..... real bad... the noise was definitely comming from the op-amp. for sure. Posted below are the recordings for the DSO-5200 but i need to figure out how to convert it into movie format, not sure how to do it. maybe ill just upload one frame of it.
After replacing the TL072 the noise and motorboating went away, and i had pretty loud audio. unfortunately, it was distorted even at low volume. Not distorted as if it were clipped off on one of the rails, that has a distinct distortion.
This one had almost like an overdrive style of distortion. But unfortuantely didnt didnt go away even at low volume from the MP3 player. it could be caused from the player, im not sure yet. however, i do have sound. its not the strongest in the world, but i do have sound now. even though it is totally distorted.
havent had a chance to scope it after i replaced the TL072. No, no sound with pre-amp board, so pre-amp is defective. have to worry about that later.
Here is the only scope shots i got before battery died. didnt charge it. lol. First shot is pin 1, and second shot is pin 2. the two pins adjacent to one another. basically, the 2 pins comming from op-amp. which is 1 and 3 i think? heck i cant remember, but it was probed from where the jumpers were..... other pins had nothing. Also scoped the + and -15v and both are clean.
Here is the only scope shots i got before battery died. didnt charge it. lol. First shot is pin 1, and second shot is pin 2. the two pins adjacent to one another. basically, the 2 pins comming from op-amp. which is 1 and 3 i think? heck i cant remember, but it was probed from where the jumpers were..... other pins had nothing. Also scoped the + and -15v and both are clean.
Attachments
This is for an MTX 4501 but it should be the same as yours.
The pin nearest the corner of the header is connected to pin 7 of the RCA op-amp. The pin to its left is connected to pin 1 of the RCA op-amp.
With 1v AC at 100Hz into the RCAs, I have 0.40v on both of those pins in the header (using either the shield ground or the chassis ground as the reference). With the multimeter's probes across those two pins, I have 0.80v.
Both pins have a clean sine wave (except for some high frequency noise that's leaking in).
The pin nearest the corner of the header is connected to pin 7 of the RCA op-amp. The pin to its left is connected to pin 1 of the RCA op-amp.
With 1v AC at 100Hz into the RCAs, I have 0.40v on both of those pins in the header (using either the shield ground or the chassis ground as the reference). With the multimeter's probes across those two pins, I have 0.80v.
Both pins have a clean sine wave (except for some high frequency noise that's leaking in).
Can you get a wav file converted and into your mp3 player?
http://www.bcae1.com/temp/100hz300seconds.zip
http://www.bcae1.com/temp/100hz300seconds.zip
Amplifier is repaired and operational. FINALLY....
I found 2 more of those pesky a$$ 10ohm resistors open on the final TL074, i only had TL084s lying around, so i swapped the last TL074 on the pre-amp, along with its 2 10ohm resistors. That fixed the preamp, and i had sound. however it was STILL distorted.
So, i scoped the gates of the mosfets using 100hz signal, one side of the amp only had maybe a 4V P-P drive, while the other side was totally off the max scale of my scope. assuming 20 or 30v p-p
So right there, i knew there was a problem. Read the voltages at the 3120 drivers, one of the drivers had 18V on it, other driver had 0.5v on it. bingo....
Found shorted 15V zener and NPN SMD transistor. replaced both, amp now operational. thanks all...
I found 2 more of those pesky a$$ 10ohm resistors open on the final TL074, i only had TL084s lying around, so i swapped the last TL074 on the pre-amp, along with its 2 10ohm resistors. That fixed the preamp, and i had sound. however it was STILL distorted.
So, i scoped the gates of the mosfets using 100hz signal, one side of the amp only had maybe a 4V P-P drive, while the other side was totally off the max scale of my scope. assuming 20 or 30v p-p
So right there, i knew there was a problem. Read the voltages at the 3120 drivers, one of the drivers had 18V on it, other driver had 0.5v on it. bingo....
Found shorted 15V zener and NPN SMD transistor. replaced both, amp now operational. thanks all...
Well guess what, shes back on the bench again. customer complained that it was working one day, then next day it quit.
Checked things out, my 15v regs are still rock solid. but the TL072 by the RCA jacks, i have -12v sitting on pin8 where 15v supposed to be. the 100ohm resistor feeding pin8 is open.
any ideas?
Checked things out, my 15v regs are still rock solid. but the TL072 by the RCA jacks, i have -12v sitting on pin8 where 15v supposed to be. the 100ohm resistor feeding pin8 is open.
any ideas?
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