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Class d amp repair help.
Class d amp repair help.
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Old 27th October 2019, 10:41 PM   #81
petercourt is offline petercourt  Australia
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Join Date: Sep 2011
Location: queensland
Quote:
Originally Posted by Perry Babin View Post
None of the op-amps should have any more than about 25mv. There's no exact number but a volt or more for any op-amp in use (sometimes only half of the op-amp is used) is likely indicative or a problem. To know if an op-amp is defective, you have to look at the voltage on the op-amp input terminals and see if the output is what it should be for the two input voltages.

The following page will help you to understand op-amps:
Operational Amplifiers
HI yes I had a read over that before. However I was not very good in school.

So having a look over these op amps some outputs being 10v. 1 being 5v. And all the rest nothing would suggest we have a problem?

I just checked black probe on ground, positive to the vcc+ inputs of all of them. And they are all 11.6vDC.
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Old 27th October 2019, 10:46 PM   #82
Perry Babin is offline Perry Babin  United States
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15 is a generic term. It could be 9v to 18v.

Excessive DC is an issue but not all with DC will be defective since they're all essentially in series and one defective op-amp could cause the later ones to have varying levels of DC.

I don't think you should make any conclusions with the pot being defective or out of the circuit.
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Old 27th October 2019, 10:51 PM   #83
petercourt is offline petercourt  Australia
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Join Date: Sep 2011
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Quote:
Originally Posted by Perry Babin View Post
15 is a generic term. It could be 9v to 18v.

Excessive DC is an issue but not all with DC will be defective since they're all essentially in series and one defective op-amp could cause the later ones to have varying levels of DC.

I don't think you should make any conclusions with the pot being defective or out of the circuit.
That pot is essentially only connected to 2 traces on the board.
Yes the board links a few of those pins together.
Last night I put a 15kohm resistor across both those points but still no audio. No protect

Being that it's a b20k pot. 15k ohms should have made it come to life but no such luck.

I'll just wait for the pot to arrive. But since shipping takes quiet a while here if I have to order any of those 4560d chips it will take queit a while.
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Old 29th October 2019, 04:46 AM   #84
petercourt is offline petercourt  Australia
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Here is the output section scematic if anyone has any ideas on that to check?

I've checked all the resistors in circut with the bass boost the IC chip seems to be OK? I'm not sure how to test it..
Attached Files
File Type: pdf M5150 A-Model pre.pdf (248.3 KB, 1 views)
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Old 29th October 2019, 07:07 AM   #85
Perry Babin is offline Perry Babin  United States
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If you're not willing to learn how op-amps work, you'll need to post the DC voltage on all pins of all of the preamp op-amps. Copy and paste the following, giving the IC's circuit board designation. Post for one IC so we can see if you're doing it right. Then you can post for the rest. For the most accurate results, it's best to find a ground closer to the op-amps. If R101 is within tolerance, you can use the RCA shields for the black probe. Do this with no signal source connected to the amp.

{IC designation here}
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
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Old 29th October 2019, 08:05 AM   #86
petercourt is offline petercourt  Australia
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Quote:
Originally Posted by Perry Babin View Post
If you're not willing to learn how op-amps work, you'll need to post the DC voltage on all pins of all of the preamp op-amps. Copy and paste the following, giving the IC's circuit board designation. Post for one IC so we can see if you're doing it right. Then you can post for the rest. For the most accurate results, it's best to find a ground closer to the op-amps. If R101 is within tolerance, you can use the RCA shields for the black probe. Do this with no signal source connected to the amp.

{IC designation here}
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
HI prrry it's not that I don't want to learn. This is just a bit over my head. I learn by doing kind of thing.
I have never had an issue with the op amp section before so this is all new.

My results are as follows for ic109. (all DC)
Pin1- 10.8v
Pin2- 10.8v
Pin3- 10.8v
Pin4- -11.6v
Pin 5- 0.9v
Pin6- 1.9v
Pin7- 10.8v
Pin8- 11.6v.

The reason I'm stopping here as when I had the negitive probe on the RCA shield. And I touched positive to pin #5 the Amp went into protect. I kept the probe there then when it came out I read 0.9vDC.
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Old 29th October 2019, 08:38 AM   #87
petercourt is offline petercourt  Australia
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IC 105.
Pin1: - 0.14
Pin 2: - 0.6
Pin 3: - 0.28
Pin4: - 11.6
Pin5: - 0.6
Pin6: - 0.6
Pin7: - 0.6v
Pin8: 11.6

Ic107.
Pin1: - 10.4
Pin2: - 10.4
Pin3: - 10.1
Pin4: - 11.6
Pin5: - 0.9
Pin6: - 0.8
Pin7: - 0.6
Pin8: 11.6

Ic108
Pin1: - 10.4
Pin2: - 10.4
Pin3: - 10.1
Pin4: - 11.6
Pin5: 0.3
Pin6: - 0.1
Pin7: - 0.1
Pin8: 11.6

Ic104
Pin1: - 0.2
Pin2: - 0.2
Pin3: - 0.2
Pin4: - 11.6
Pin5: 0.2
Pin6: - 0. 2
Pin7: - 0.2
Pin8: 11.6

Just unplugged the Amp for a bit don't want to keep it powered for too long.
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Old 29th October 2019, 09:22 AM   #88
Perry Babin is offline Perry Babin  United States
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This is to all that are here looking for help, no one here was born knowing this stuff. Some learn it easily and some struggle... but CAN get it if they try. There are things people need to fully understand. The operation of the driver ICs (especially the TL494) is one. Most will replace hundreds of these that are working perfectly instead of learning how the IC functions. It's so important that if a tech has to spend 8 hours or more doing nothing but studying this IC, it's time well spent because it takes a few seconds and costs nothing to measure the voltage on the terminals to see if the problem is with the IC or elsewhere. Over the years, it saves FAR more than the 8, 10... whatever hours it takes to learn it.

The same goes for op-amps. If it takes a couple of weeks of hard studying to fully understand them, it's time well spent.

Did you check R101?
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Old 29th October 2019, 09:32 AM   #89
petercourt is offline petercourt  Australia
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Join Date: Sep 2011
Location: queensland
Quote:
Originally Posted by Perry Babin View Post
This is to all that are here looking for help, no one here was born knowing this stuff. Some learn it easily and some struggle... but CAN get it if they try. There are things people need to fully understand. The operation of the driver ICs (especially the TL494) is one. Most will replace hundreds of these that are working perfectly instead of learning how the IC functions. It's so important that if a tech has to spend 8 hours or more doing nothing but studying this IC, it's time well spent because it takes a few seconds and costs nothing to measure the voltage on the terminals to see if the problem is with the IC or elsewhere. Over the years, it saves FAR more than the 8, 10... whatever hours it takes to learn it.

The same goes for op-amps. If it takes a couple of weeks of hard studying to fully understand them, it's time well spent.

Did you check R101?
HI yes r101 reads 220ohm in circut.

I also notice if I touch pin 5 of ic109 with my finger amp goes into protect.
I may also add there is no bass boost pot installed on the board. It should arrive tomorrow hopefully.

Ic109 seems to be part of the bass boost circut.
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Old 31st October 2019, 04:03 AM   #90
petercourt is offline petercourt  Australia
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Join Date: Sep 2011
Location: queensland
So just an update.
I replaced the b20k pot however it's still going into protect.
I had a bit more of a dig around and found the right input for the RCA has a broken rca shield off the board. This would explain the lack of power.

I have just organized to get it shipped out for repair as it will need a new rca input block. Something the company won't sell me.

As far as the protect. Well I don't have any idea. Hopefully the repair company will find the issue.
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