Sound issues

ItsTheSmell · 01 July 2018, 12:52

I own 2 1200s rev 1D.4 and the sound is distorted on both of them. I had the audio chip replaced which seemed to solve it but now its back. The music in Dune is so distorted you cant listen to it. Ive tried the WHDload version and the adf from emuparadise and both are the same. Its been recapped so im at a loss as to why this is happening, any ideas anyone? Ive an a500+ and the audio is fine on that so its not the adf.

fordav1 · 01 July 2018, 13:17

it's one of the common problems on the A1200. The 22uF SMD caps leaks and screw the board where the op amp is. There are also 22uF caps near the audio jack outputs. You need to remove all the affected parts, clean it up and replace with new parts, while checking to make sure there are no broken tracks etc.
If it has been recapped then whoever did it didn't properly clean it and the corrosive fluid from the leaked caps has gotten into the vias. That causes broken tracks between top and bottom of the board where that via is. There could be multiple places and multiple bad vias. Leaky caps causing open vias is the no.1 cause of problems on the A1200 and A600

ItsTheSmell · 01 July 2018, 13:25

as far as i know the caps havent leaked. one of the boards was recapped by someone else who didnt do a very good job and the guy who recapped the other board redid the recap, he replaced the opamp but it was still distorted so he replaced the caps of which some smelt fishy. he couldnt find any damage to the board.

fordav1 · 01 July 2018, 14:37

As I said, very common to see A1200 with sound related issues. I've fixed dozens of them. There's always a leaking cap even if it doesn't look like it and it slowly eats at the vias even if removed and replaced. Once it leaks the damage doesn't go away just because the cap is replaced. There's always a dodgy via or some corrosion in the area near the 22uF SMD caps or the 10uF cap (all near the LF347). The easiest way is remove all the parts and check the PCB, then test the parts using a cheap component tester (ebay etc) then put them back together with new parts if they are out of spec or damaged.
Here's some pics from an A600 I did last year....

Solderbro · 01 July 2018, 18:05

Be careful, i grilled a new cerko when soldering in , now there is no sound at right channel. These cerko types 22uF 16V are rare and available 6V types maybe burn through.

Daedalus · 01 July 2018, 20:59

Have you checked the PSU? If the +12V or -12V supplies aren't working properly you'll get audio distortion, but the computer itself will boot and run fine once the 5V rail is working. Another fault I've seen a couple of times is a failure of resistors in the power supply path to the audio circuitry, essentially doing the same thing as a failed +/-12V rail, but localised to the audio portion of the board. Check R301 and R302, they should both be 10 ohms, and pins 4 and 11 of U15 should be +12V and -12V respectively.

FOL · 02 July 2018, 10:23

I would also check the bottom of the board under that area. Maybe track going through board is damaged. When you have alot of leakage it normally makes its way through to other side of board.

ItsTheSmell · 02 July 2018, 10:41

Quote:

Originally Posted by Daedalus

Have you checked the PSU? If the +12V or -12V supplies aren't working properly you'll get audio distortion, but the computer itself will boot and run fine once the 5V rail is working. Another fault I've seen a couple of times is a failure of resistors in the power supply path to the audio circuitry, essentially doing the same thing as a failed +/-12V rail, but localised to the audio portion of the board. Check R301 and R302, they should both be 10 ohms, and pins 4 and 11 of U15 should be +12V and -12V respectively.

originally, i had a brick psu that was putting out -18v into the op amp which is why I got it replaced on both 1200s. the newer psu seemed to be putting out -12v into the opamp once the psu was connected. ive since purchased a brand new psu so this cannot be the cause any longer. Do any of you live in the uk?

Daedalus · 02 July 2018, 10:50

Quote:

Originally Posted by ItsTheSmell

originally, i had a brick psu that was putting out -18v into the op amp which is why I got it replaced on both 1200s. the newer psu seemed to be putting out -12v into the opamp once the psu was connected.

Hmmm, -18 could possibly have damaged the op amp. And you haven't used the old PSU on the machine since you fitted the new op-amp? If you use the old PSU with the new op-amp, that could have done the same damage to the replacement part.

Quote:

ive since purchased a brand new psu so this cannot be the cause any longer.

If the op-amp was already damaged, switching to a good PSU won't fix it.

Quote:

Do any of you live in the uk?

Yep, lots of us

There might be someone not too far from where you are who could give a hand.

Quote:

How do I test the ohms on r301 and r302?

With the power off, use a multimeter's resistance setting and touch either end of the resistor with the probes. It should be around 10 ohms in both cases. Better still would be to measure the resistance between the power rails and the relevant power pins of the op-amp, which will tell you whether the whole power supply circuit is intact.

Sim085 · 02 July 2018, 14:45

When you say distorted do you mean something like this:
https://www.dropbox.com/s/o50yq6te44...04933.mp4?dl=0

ItsTheSmell · 02 July 2018, 21:15

Quote:

Originally Posted by Sim085

When you say distorted do you mean something like this:
https://www.dropbox.com/s/o50yq6te44...04933.mp4?dl=0

no as bad as that, the music can still be heard but the level is too high so it leads into distortion.

The opamp is new on both machines and the dodgy psu has been binned so I havent damaged the opamp again. It could possibly be the 2nd psu i used was faulty but as far as i can tell its working ok. the 3rd psu is brand new.

ItsTheSmell · 03 July 2018, 18:53

Quote:

Originally Posted by Daedalus

With the power off, use a multimeter's resistance setting and touch either end of the resistor with the probes. It should be around 10 ohms in both cases. Better still would be to measure the resistance between the power rails and the relevant power pins of the op-amp, which will tell you whether the whole power supply circuit is intact.

R301 reads 10.8, R302 is 11 (multimeter set to Ohms 200. Does this make any difference?

FOL · 03 July 2018, 23:48

Quote:

Originally Posted by Daedalus

Hmmm, -18 could possibly have damaged the op amp. And you haven't used the old PSU on the machine since you fitted the new op-amp? If you use the old PSU with the new op-amp, that could have done the same damage to the replacement part.

If the op-amp was already damaged, switching to a good PSU won't fix it.

Yep, lots of us

There might be someone not too far from where you are who could give a hand.

With the power off, use a multimeter's resistance setting and touch either end of the resistor with the probes. It should be around 10 ohms in both cases. Better still would be to measure the resistance between the power rails and the relevant power pins of the op-amp, which will tell you whether the whole power supply circuit is intact.

Just so you know, -18 is normal offload. I have a few PSU's here that read that and have been working fine for around 10 years of 8 hour daily usage.

FOL · 03 July 2018, 23:52

Quote:

Originally Posted by ItsTheSmell

R301 reads 10.8, R302 is 11 (multimeter set to Ohms 200. Does this make any difference?

Check the transistors below the opamp. What do they read voltage wise.
Do you have your +12 and -12 actually on the opamp itself?

Daedalus · 04 July 2018, 00:09

Quote:

Originally Posted by FOL

Just so you know, -18 is normal offload. I have a few PSU's here that read that and have been working fine for around 10 years of 8 hour daily usage.

Yep, fair point. I assumed it was being measured at the op amp with this, but I might've picked it up wrong...

Quote:

originally, i had a brick psu that was putting out -18v into the op amp

ItsTheSmell · 04 July 2018, 08:37

Thanks for getting back to me, the -18v was read from the centre (back side) of the opamp, the centre (user side) was reading at +12v. I tested the psu i had recently purchased into the 1200 and the opamp was @ +/-12v into the opamp. I had the opamps replaced after finding this. So is the psu dodgy? The amiga ran fine on it, just with sound level distorion but I cant find out the cause, I bought a 2nd amiga and it turned up with the same rev board and the same distortion but I used the same psu.

Daedalus · 04 July 2018, 10:17

Yeah, that sounds like the PSU was indeed dodgy. An Amiga will run mostly fine once the 5V supply is ok - the digital circuits don't care about the 12V rails so it will run fine with the exception of audio and serial when there's a problem with them.

ItsTheSmell · 04 July 2018, 16:48

Ive tried to do a continuity test on all of the resistors below the opamp and hardly any give me a reading (with the power off) should I get a readout/buzzer sound when tested? Im a novice with electronics.

Daedalus · 04 July 2018, 17:14

No, the continuity test only beeps when there is below a certain resistance between the probes, usually around 20-30 ohms. Anything above that won't beep, so to check those resistors, use the resistance setting of your meter instead and read the value off the display. It should be roughly what is given on the schematic, though there are certain cases where that might not be the case.

ItsTheSmell · 04 July 2018, 17:23

its not giving me a reading on any of them (mm set to ohms 200) but the power to the amiga board is off, should it be on?

01 July 2018, 12:52	#1
ItsTheSmell Registered User Join Date: Mar 2018 Location: New Ferry Posts: 516	Sound issues I own 2 1200s rev 1D.4 and the sound is distorted on both of them. I had the audio chip replaced which seemed to solve it but now its back. The music in Dune is so distorted you cant listen to it. Ive tried the WHDload version and the adf from emuparadise and both are the same. Its been recapped so im at a loss as to why this is happening, any ideas anyone? Ive an a500+ and the audio is fine on that so its not the adf.

01 July 2018, 13:25	#3
ItsTheSmell Registered User Join Date: Mar 2018 Location: New Ferry Posts: 516	leaking caps as far as i know the caps havent leaked. one of the boards was recapped by someone else who didnt do a very good job and the guy who recapped the other board redid the recap, he replaced the opamp but it was still distorted so he replaced the caps of which some smelt fishy. he couldnt find any damage to the board.

01 July 2018, 14:37	#4
fordav1 Registered User Join Date: Jan 2017 Location: Australia Posts: 84	As I said, very common to see A1200 with sound related issues. I've fixed dozens of them. There's always a leaking cap even if it doesn't look like it and it slowly eats at the vias even if removed and replaced. Once it leaks the damage doesn't go away just because the cap is replaced. There's always a dodgy via or some corrosion in the area near the 22uF SMD caps or the 10uF cap (all near the LF347). The easiest way is remove all the parts and check the PCB, then test the parts using a cheap component tester (ebay etc) then put them back together with new parts if they are out of spec or damaged. Here's some pics from an A600 I did last year.... Attached Thumbnails

02 July 2018, 14:45	#10
Sim085 Registered User Join Date: Apr 2009 Location: N/A Posts: 962	When you say distorted do you mean something like this: https://www.dropbox.com/s/o50yq6te44...04933.mp4?dl=0 Last edited by Sim085; 02 July 2018 at 18:32. Reason: Put correct link

04 July 2018, 08:37	#16
ItsTheSmell Registered User Join Date: Mar 2018 Location: New Ferry Posts: 516	Thanks for getting back to me, the -18v was read from the centre (back side) of the opamp, the centre (user side) was reading at +12v. I tested the psu i had recently purchased into the 1200 and the opamp was @ +/-12v into the opamp. I had the opamps replaced after finding this. So is the psu dodgy? The amiga ran fine on it, just with sound level distorion but I cant find out the cause, I bought a 2nd amiga and it turned up with the same rev board and the same distortion but I used the same psu. Last edited by ItsTheSmell; 04 July 2018 at 08:38. Reason: spelling

01 July 2018, 13:17	#2
fordav1 Registered User Join Date: Jan 2017 Location: Australia Posts: 84	it's one of the common problems on the A1200. The 22uF SMD caps leaks and screw the board where the op amp is. There are also 22uF caps near the audio jack outputs. You need to remove all the affected parts, clean it up and replace with new parts, while checking to make sure there are no broken tracks etc. If it has been recapped then whoever did it didn't properly clean it and the corrosive fluid from the leaked caps has gotten into the vias. That causes broken tracks between top and bottom of the board where that via is. There could be multiple places and multiple bad vias. Leaky caps causing open vias is the no.1 cause of problems on the A1200 and A600

01 July 2018, 18:05	#5
Solderbro Registered User Join Date: Jun 2018 Location: Hamburg Age: 55 Posts: 56	Be careful, i grilled a new cerko when soldering in , now there is no sound at right channel. These cerko types 22uF 16V are rare and available 6V types maybe burn through.

01 July 2018, 20:59	#6
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,335	Have you checked the PSU? If the +12V or -12V supplies aren't working properly you'll get audio distortion, but the computer itself will boot and run fine once the 5V rail is working. Another fault I've seen a couple of times is a failure of resistors in the power supply path to the audio circuitry, essentially doing the same thing as a failed +/-12V rail, but localised to the audio portion of the board. Check R301 and R302, they should both be 10 ohms, and pins 4 and 11 of U15 should be +12V and -12V respectively.

02 July 2018, 10:23	#7
FOL PSPUAE DEV Join Date: Nov 2006 Location: Wales / UK Age: 45 Posts: 5,999	I would also check the bottom of the board under that area. Maybe track going through board is damaged. When you have alot of leakage it normally makes its way through to other side of board.

04 July 2018, 10:17	#17
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,335	Yeah, that sounds like the PSU was indeed dodgy. An Amiga will run mostly fine once the 5V supply is ok - the digital circuits don't care about the 12V rails so it will run fine with the exception of audio and serial when there's a problem with them.

04 July 2018, 16:48	#18
ItsTheSmell Registered User Join Date: Mar 2018 Location: New Ferry Posts: 516	Ive tried to do a continuity test on all of the resistors below the opamp and hardly any give me a reading (with the power off) should I get a readout/buzzer sound when tested? Im a novice with electronics.

04 July 2018, 17:14	#19
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,335	No, the continuity test only beeps when there is below a certain resistance between the probes, usually around 20-30 ohms. Anything above that won't beep, so to check those resistors, use the resistance setting of your meter instead and read the value off the display. It should be roughly what is given on the schematic, though there are certain cases where that might not be the case.

04 July 2018, 17:23	#20
ItsTheSmell Registered User Join Date: Mar 2018 Location: New Ferry Posts: 516	its not giving me a reading on any of them (mm set to ohms 200) but the power to the amiga board is off, should it be on? Last edited by ItsTheSmell; 04 July 2018 at 19:01.

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