Please post the voltages on the two op-amps near the 3120s.
Op-amp closest to 3120s
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Other op-amp
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Is the large copper area connected to R414 connected directly to the + speaker output?
Op-amp closest to 3120s
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Other op-amp
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Is the large copper area connected to R414 connected directly to the + speaker output?
Those are not what I'd expect. Even taking into account that the outputs have been removed, the voltages should be significantly different. For example, the two inputs to each op-amp should match. If they don't match within ~0.01v, the output should swing as far as it can (within the limits of the power supply) to try to make them match.
Since the last post, someone dropped off an MTX 81001D. It's close enough to use as a guide to help. I'm going to go through it to see if I can find anything that could produce the 8v on the output.
The following voltages are from the 810001D.
Op-amp closest to 3120s
Pin 1: -6.15
Pin 2: 0.034
Pin 3: 0.035
Pin 4: -15.32
Pin 5: -5.91
Pin 6: -5.86
Pin 7: -0.07
Pin 8: 15.07
Other op-amp
Pin 1: 0.018
Pin 2: 0.004
Pin 3: 0.003
Pin 4: -15.32
Pin 5: 0.005
Pin 6: 0.005
Pin 7: 0.011
Pin 8: 15.08
Does the 7801 have an LM311 near the 15v reg?
Since the last post, someone dropped off an MTX 81001D. It's close enough to use as a guide to help. I'm going to go through it to see if I can find anything that could produce the 8v on the output.
The following voltages are from the 810001D.
Op-amp closest to 3120s
Pin 1: -6.15
Pin 2: 0.034
Pin 3: 0.035
Pin 4: -15.32
Pin 5: -5.91
Pin 6: -5.86
Pin 7: -0.07
Pin 8: 15.07
Other op-amp
Pin 1: 0.018
Pin 2: 0.004
Pin 3: 0.003
Pin 4: -15.32
Pin 5: 0.005
Pin 6: 0.005
Pin 7: 0.011
Pin 8: 15.08
Does the 7801 have an LM311 near the 15v reg?
I can't find anything that would cause 8v to appear on the outputs. It's a low current source so it's not a significant problem. When you power up the amp, connect a speaker or dummy load to the amp to keep the DC at a minimum. If you use a speaker, make sure that the DC is less than 1v when the amp is powered up.
At this point, I'd suggest that you reinstall the outputs and replace the two op-amps (NE5532s) near the 3120s.
Have you ever replaced any SMD ICs?
Do you have any kapton tape?
Has the red LED near the 3120s (LED400) ever lit up?
At this point, I'd suggest that you reinstall the outputs and replace the two op-amps (NE5532s) near the 3120s.
Have you ever replaced any SMD ICs?
Do you have any kapton tape?
Has the red LED near the 3120s (LED400) ever lit up?
#12 on the video clips page. Read the notes under the image.
The area has VERY tight spacing between components. If you use the Kapton, you can cover the other parts so that the IC can't stick to them as you move the op-amp off of the pads. If you don't want to buy the tape, you can try lifting the IC after the solder is hot enough on ALL of the legs. You must be careful not to lift before the solder is hot enough. If you aren't patient, you could lift one or more of the pads.
As an alternative, you can desolder one side at a time. Apply additional solder to one row of legs and get the entire row hot by running the iron back and forth across the legs. When it's hot enough, use a small screwdriver to lift the chip to a 20-30 degree angle. Hold it there until the solder cools. Use desoldering braid to remove the solder from the side that you lifted. When you go to the other side, you'll lift the IC as soon as the solder is hot enough.
The area has VERY tight spacing between components. If you use the Kapton, you can cover the other parts so that the IC can't stick to them as you move the op-amp off of the pads. If you don't want to buy the tape, you can try lifting the IC after the solder is hot enough on ALL of the legs. You must be careful not to lift before the solder is hot enough. If you aren't patient, you could lift one or more of the pads.
As an alternative, you can desolder one side at a time. Apply additional solder to one row of legs and get the entire row hot by running the iron back and forth across the legs. When it's hot enough, use a small screwdriver to lift the chip to a 20-30 degree angle. Hold it there until the solder cools. Use desoldering braid to remove the solder from the side that you lifted. When you go to the other side, you'll lift the IC as soon as the solder is hot enough.
Perry Babin said:
Those are the new measurements after replacing the op-amps.
Now on the 3120 closest to the output fets I get:
Between pin 5-8 = -15.5V
Between pin 2-3 = 0.11V
Between pin 5-6 = -0.199V
Other 3120
Between pin 5-8 = -14.68V
Between pin 2-3 = 0.111V
Between pin 5-6 = -4.88V
I still get DC across the outputs, at first I got 1.5V DC, then after powering off the amp and powering it back on because the OP-Amp furthest from the 3120's was getting hot, the DC output now is 4.11V and 3.96V with a 220 ohm resistor across it.
Still no output. I tried to test the pins individually on the 3120's and this is what I got below:
3120 closest to output fets:
Pin 1:0.011
Pin 2:0.426
Pin 3:0.453
Pin 4:0.003
Pin 5:-84.2
Pin 6:-84.2
Pin 7:-84.2
Pin 8:-69
The other one:
Pin 1:0.009
Pin 2:0.269
Pin 3:0.376
Pin 4:0.014
And on pins 5 to 8 what ever it was caused my meter to go crazy, couldn't get any ready in DC, AC, or frequency on my DMM, it just made the screen go nuts. ?
The op-amps appear to be working normally now but there's a problem with the voltage readings. When troubleshooting, you need accurate numbers.
If you look at the voltages on pin 4 of both op-amps and on pin 8 of both op-amps, you can see a big difference. If you check the board, you'll find that there's a direct connection from 4-4 and from 8-8. You shoud read precisely the same voltage on pin 8 of both op-amps and the same voltage on pin 4 of both op-amps. If there's more than a 0.01v difference, you need to determine why.
It appears that pin 1 and pin 2 of the op-amp (the one with 0.45v on those pins - let's call it op-amp A) may have the pins shorted together. If they are shorted together, fix that and then check for DC on the output.
When you measure the voltage between pins 5-6, 5-8 on the 3120s, place the black meter lead on pin 5.
The meter probably had trouble reading the voltage on pins 5 to 8 because they're floating and have a rail to rail square wave on them.
If you look at the voltages on pin 4 of both op-amps and on pin 8 of both op-amps, you can see a big difference. If you check the board, you'll find that there's a direct connection from 4-4 and from 8-8. You shoud read precisely the same voltage on pin 8 of both op-amps and the same voltage on pin 4 of both op-amps. If there's more than a 0.01v difference, you need to determine why.
It appears that pin 1 and pin 2 of the op-amp (the one with 0.45v on those pins - let's call it op-amp A) may have the pins shorted together. If they are shorted together, fix that and then check for DC on the output.
When you measure the voltage between pins 5-6, 5-8 on the 3120s, place the black meter lead on pin 5.
The meter probably had trouble reading the voltage on pins 5 to 8 because they're floating and have a rail to rail square wave on them.
Well, I replaced op-amp A, the one that looked shorted, and I checked for continuity between all the combinations on each op amp and theres nothing shorted, but the numbers did change, however it still gets pretty warm compared to the other op-amp closer to the 3120's
The new numbers are below.
And now the 3120 closest to the output fets
Black leads on 5
5-8 =+15.55V
5-6 =+0.42V
Other 3120
5-8 =+14.82V
5-6 =+5.59V
DC on the output is still present , now 5.82V
Could there be a faulty 3120 causing this trouble, if im not mistaken, shouldn't pin 5/6 and 2/3 have opposite polarities from each other?
The op-amps are NE5532DX's from Fairchild that I ordered, the originals were NE5532's.
The new numbers are below.
Perry Babin said:
And now the 3120 closest to the output fets
Black leads on 5
5-8 =+15.55V
5-6 =+0.42V
Other 3120
5-8 =+14.82V
5-6 =+5.59V
DC on the output is still present , now 5.82V
Could there be a faulty 3120 causing this trouble, if im not mistaken, shouldn't pin 5/6 and 2/3 have opposite polarities from each other?
The op-amps are NE5532DX's from Fairchild that I ordered, the originals were NE5532's.
The numbers on the 'other' op-amp are still not what they should be. With pin 2 at a lower voltage than pin 3, the output should swing positive.
Also, the output from pin 1 goes to pin 2 of the op-amp closest to the 3120s via a 2k ohm resistor. You should see essentially the same voltage on those 2 pins.
Re-check the voltages. Power up the amp for a few minutes before measuring the voltage.
Does the amp have significatly less voltage across the speaker terminals (resistor across terminals) before LED400 swtches on?
Before LED400 lights up, the voltage from 5-6 on the opto-couplers should be close to 0v.
From this point on, let's refer to the op-amp closest to the edge of the board as the 'input' op-amp. The other op-amp will be the 'servo' op-amp.
servo
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
input
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Also, the output from pin 1 goes to pin 2 of the op-amp closest to the 3120s via a 2k ohm resistor. You should see essentially the same voltage on those 2 pins.
Re-check the voltages. Power up the amp for a few minutes before measuring the voltage.
Does the amp have significatly less voltage across the speaker terminals (resistor across terminals) before LED400 swtches on?
Before LED400 lights up, the voltage from 5-6 on the opto-couplers should be close to 0v.
From this point on, let's refer to the op-amp closest to the edge of the board as the 'input' op-amp. The other op-amp will be the 'servo' op-amp.
servo
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
input
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
After a 5 min warm up
servo
Pin 1: -4V
Pin 2: 0.245V
Pin 3: 0.238V
Pin 4: -14.92V
Pin 5: -3.42V
Pin 6: -3.32V
Pin 7: 0.5V
Pin 8: 16.01V
input
Pin 1: -2.3V
Pin 2: -1.08V
Pin 3: -1.01V
Pin 4: -14.92V
Pin 5: 0.235
Pin 6: 0.235
Pin 7: 0.235
Pin 8: 16.01
After a 10 min warm up and fan's "trying" to spin up.
servo
Pin 1: -2.48V
Pin 2: 0.19V
Pin 3: 0.237V
Pin 4: -14.99V
Pin 5: -2.5V
Pin 6: -2.6V
Pin 7: 0.61V
Pin 8: 16.07V
input
Pin 1: -3.1V
Pin 2: -1.4V
Pin 3: -1.39V
Pin 4: -14.99V
Pin 5: 0.232V
Pin 6: 0.231V
Pin 7: 0.229V
Pin 8: 16.07V
Pin's 5 and 6 shorted together on both op-amps cause the fans to fully turn on.
On the Servo op amp pin 7 goes to 8V , and on the Input Op-amp pin 7 goes to 15V when pins 5and 6 are shorted.
Across the ouputs with a 220 ohm resistor "before LED400 turns on", the DC voltage is below 1V.
Before LED400 lights up, the voltage between 5-6 on both opto-couplers is 0V.
I also noticed that when I probe pin 1 and pin 2 on the Servo op-amp , the fans turn on, it does not do that on the Input op-amp.
I tired to find this 2k resistor between pin and and 2 but could not see the traces good enough with my magnifying glass.
And with the amp warmed up, the DC on the outputs is just under 13VDC now.
servo
Pin 1: -4V
Pin 2: 0.245V
Pin 3: 0.238V
Pin 4: -14.92V
Pin 5: -3.42V
Pin 6: -3.32V
Pin 7: 0.5V
Pin 8: 16.01V
input
Pin 1: -2.3V
Pin 2: -1.08V
Pin 3: -1.01V
Pin 4: -14.92V
Pin 5: 0.235
Pin 6: 0.235
Pin 7: 0.235
Pin 8: 16.01
After a 10 min warm up and fan's "trying" to spin up.
servo
Pin 1: -2.48V
Pin 2: 0.19V
Pin 3: 0.237V
Pin 4: -14.99V
Pin 5: -2.5V
Pin 6: -2.6V
Pin 7: 0.61V
Pin 8: 16.07V
input
Pin 1: -3.1V
Pin 2: -1.4V
Pin 3: -1.39V
Pin 4: -14.99V
Pin 5: 0.232V
Pin 6: 0.231V
Pin 7: 0.229V
Pin 8: 16.07V
Pin's 5 and 6 shorted together on both op-amps cause the fans to fully turn on.
On the Servo op amp pin 7 goes to 8V , and on the Input Op-amp pin 7 goes to 15V when pins 5and 6 are shorted.
Across the ouputs with a 220 ohm resistor "before LED400 turns on", the DC voltage is below 1V.
Before LED400 lights up, the voltage between 5-6 on both opto-couplers is 0V.
I also noticed that when I probe pin 1 and pin 2 on the Servo op-amp , the fans turn on, it does not do that on the Input op-amp.
I tired to find this 2k resistor between pin and and 2 but could not see the traces good enough with my magnifying glass.
And with the amp warmed up, the DC on the outputs is just under 13VDC now.
http://bcae1.com/temp/P5060003b.jpg
Look at this photo. Does yours have all of the component parts?
The fans are probably controlled by the voltage on the speaker terminals. If that's the case, the higher DC voltage would trigger the fans.
Probing pin 1 of the op-amp should make no difference. Are you sure that you were only touching pin 1?
Look at this photo. Does yours have all of the component parts?
The fans are probably controlled by the voltage on the speaker terminals. If that's the case, the higher DC voltage would trigger the fans.
Probing pin 1 of the op-amp should make no difference. Are you sure that you were only touching pin 1?
Yes, mine has all the same component parts as in the picture.
I was probing pin 1 and 2, ie. red lead on pin 1, black on pin 2 for when the fans were turning on.
Now, all the voltage readings I have taken were with the ground at the main ground block for the amp, should I have been taking the measurement with the ground on the op-amp? I noticed Vcc doubles when I take the measurement from the ground on the op-amps.
I was probing pin 1 and 2, ie. red lead on pin 1, black on pin 2 for when the fans were turning on.
Now, all the voltage readings I have taken were with the ground at the main ground block for the amp, should I have been taking the measurement with the ground on the op-amp? I noticed Vcc doubles when I take the measurement from the ground on the op-amps.
When you probed pins 1 and 2, the meter was changing the input of the op-amp and that's what caused the fans to spin up. Was your meter set to ohms or diode check?
What meter are you using?
There are two things that concern me at this point.
The first is the negative input voltage on pin 3 of the input op-amp. This could be due to leakage in contaminants on the board. If you haven't already done so, clean the area thoroughly with acetone and a toothbrush. If you have compressed air, use it to force the acetone from under the IC after cleaning. Clean it twice to be sure it's clean. That may get rid of the negative DC.
The second problem is the fact that you have significant negative voltage on pin 1 of the input op-amp and positive voltage on pin 2 of the servo op-amp. We can deal with this later if necessary.
Clean the board first and post the results (more or less DC on the outputs?).
When measuring the DC voltage on the op-amps, it may be better to use the negative speaker terminals. If you measure the DC voltage from the negative speaker terminal and the chassis ground and find that it's more than 0.005v, use the -sp terminal.
What meter are you using?
There are two things that concern me at this point.
The first is the negative input voltage on pin 3 of the input op-amp. This could be due to leakage in contaminants on the board. If you haven't already done so, clean the area thoroughly with acetone and a toothbrush. If you have compressed air, use it to force the acetone from under the IC after cleaning. Clean it twice to be sure it's clean. That may get rid of the negative DC.
The second problem is the fact that you have significant negative voltage on pin 1 of the input op-amp and positive voltage on pin 2 of the servo op-amp. We can deal with this later if necessary.
Clean the board first and post the results (more or less DC on the outputs?).
When measuring the DC voltage on the op-amps, it may be better to use the negative speaker terminals. If you measure the DC voltage from the negative speaker terminal and the chassis ground and find that it's more than 0.005v, use the -sp terminal.
When I probed pin 1 and 2 together I was in DC testing.
The meter is a Mastercraft 52-0052-2, it's sold at Canadian tire (auto ranging) They buy if from a company and re package it, so im not sure who really makes it.
I did clean the area with acetone and a tooth brush before, and I did again 2 more times, this time blowing the acetone away with compressed air. The numbers did not change on the op-amps.
The DC output rises as the amp gets warmer, the fans turn on around 15.5V DC on the outputs.
I went back to check the voltages on the Output fets, and my meter is going crazy and automatically going through all the settings on the DMM when I test the outside legs of the positive output fets, and the middle leg makes it go nuts on the negitive side. It did not do this before, I was able to read the voltages before.
The meter is a Mastercraft 52-0052-2, it's sold at Canadian tire (auto ranging) They buy if from a company and re package it, so im not sure who really makes it.
I did clean the area with acetone and a tooth brush before, and I did again 2 more times, this time blowing the acetone away with compressed air. The numbers did not change on the op-amps.
The DC output rises as the amp gets warmer, the fans turn on around 15.5V DC on the outputs.
I went back to check the voltages on the Output fets, and my meter is going crazy and automatically going through all the settings on the DMM when I test the outside legs of the positive output fets, and the middle leg makes it go nuts on the negitive side. It did not do this before, I was able to read the voltages before.
With the Crossover board disconnected the op-amp voltages changed quite a few on some of the inputs.
The new voltages are as follows.
Servo (no x-over board
Pin 1: -7.5
Pin 2: 0.03
Pin 3: 0.001
Pin 4: -15.22
Pin 5: -7.1
Pin 6: -7
Pin 7: -0.384
Pin 8: 15.81
Input (no x-over board)
Pin 1: -0.004
Pin 2: -0.001
Pin 3: -0.002
Pin 4: -15.22
Pin 5: -0.002
Pin 6: -0.001
Pin 7: -0.003
Pin 8: 15.81
3120's
Closest to ouput fets:
5-6: 0.5V
5-8: 15.61V
Other
5-6: 5.26V
5-8: 14.93V
The new voltages are as follows.
Servo (no x-over board
Pin 1: -7.5
Pin 2: 0.03
Pin 3: 0.001
Pin 4: -15.22
Pin 5: -7.1
Pin 6: -7
Pin 7: -0.384
Pin 8: 15.81
Input (no x-over board)
Pin 1: -0.004
Pin 2: -0.001
Pin 3: -0.002
Pin 4: -15.22
Pin 5: -0.002
Pin 6: -0.001
Pin 7: -0.003
Pin 8: 15.81
3120's
Closest to ouput fets:
5-6: 0.5V
5-8: 15.61V
Other
5-6: 5.26V
5-8: 14.93V
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