At the highly probable risk of being TLDR; A little bit of backstory.
I was a single amiga owner. My trusty 1200 and I had been through a lot together and I'd learnt a lot about modern computing from it.
My introduction on here ( https://www.amibay.com/showthread.php?t=35759 ) describes how I acquired my 1200 and some of the things I did with it. From it I learnt to program, to render, to paint, to diagram, to word process, to compose "music", to edit sound, to type (oh so many hours on IRC), to administrate, how complex multiprocessor and I/O systems worked, about multitasking, and a sort of rough idea of how it was engineered to do all the wonderful things it did.
MS-DOS and Windows PCs, even the mighty macintosh, held no interest for me.
Many years later when my good friend (from many years of Amiga related learning and fun as well as being a cool guy) gifted me his old A4000/030 I was thrilled.
For the entire life I've known this machine the sound had always been overtly distorted. I didn't care, but I did decide to look into why it didn't work at some time. After all how hard could it be to replace even the op amp if that was what was broken.
Roll forward a few more years, a house move and plenty of other changes. I get the pleasure of meeting some new Amigans at work.
One of them in particular seems to feel he missed the boat a bit due to his being 10 years my junior and is now rapidly making up for it. So he's a bit keen to poke around and I'm more than happy to assist and advise. He's currently the owner of at least a CD32, an A600, one or more A500 and recently an A4000.
Sometime during this recent time I did some research into the audio system on the A4000 and came across a great guy in New Zealand who was able to give me some pointers and great advice, both via his web site and via email.
I finally got around to taking it apart, and started cleaning it gently with IPA and a soft toothbrush, taking extreme care around some of the obvious damage.
I removed the corrosion I could see and the badly furred battery and cleaned up the amp circuitry. I then set to testing various elements and came to the conclusion it was the vref to the op amp that was at fault.
Not really having the space for any serious work on it I carried on cleaning the whole board and de-fluffing the insides, might as well preserve what I can.
Another 6 months pass.
You are in a wild forest. To the north is a dark path.
To the south is a slightly less dark path.
>
Suddenly a weekend appears, where some how the avid Amiga Collector has offered me use of his kitchen, tools and services to have a go at finding out exactly what is wrong with the audio. With it always being much nicer having a fellow Amigan at hand for ideas and assistance I wasn't going to pass up the opportunity. The kitchen, tools and skills an added bonus.
This about about how far away my eyes focus sharply.
I'm fairly skilled with a soldering iron and a multimeter, and an oscilloscope, if one is at hand (we don't have one). I can read schematics and translate them to circuits. But hell this 1206 stuff is small; and therefore scary to a good old discrete guy like me. Now I know 1206 is considered huge these days and there are bound to be guys (and hopefully gals) on here who are laughing out loud at me stating 1206 is small, but I'm hoping the general consensus will be it's scary.
On with the prOn.
So take it apart. Might as well do something fun.
The next job is read, and refresh the grey matter on simple op-amp circuits, compare schematic with board and turn it over lots.
Next job is think, apply logic and do some more reading to confirm possible theories. Think of tests that will confirm these theories.
And stare at the board some more.
So for some of the tests we're going to need it powered up, guess we need to work out what is the minimum configuration for an operational Rev B A4000.
Voila, it shows us the begging screen. One motherboard, cpu daughterboard, some chip ram, some fast ram and the all important PSU.
It does help to know which way the composite/RGB switch on the back of the monitor should be before trying this excercise.
Inspect stuff.
VIAs. Oooh grubby. We'll give them a poke later.
A damaged DC filter cap connection.
Gratuitous Amiga computer city shots.
Gratuitious Photography setup shot.
The Amiga Collector is busy reading elsewhere, so I do a bit more cleaning from the review of the macro shots. I get a thin bit of wire and poke some of the vias clean.
Okay so time to do some actual testing. After a little bit more refreshing the grey matter I work out I need to test the voltages at either end of both r401 and r402.
Hmm this meter seems to have a broken negative sign. Switch meter.
Yep definitely a problem there. The 0.45v should be 2.5v. The Amiga Collector is reading stuff elsewhere so I call him over to show him. And the problem disappears.
Over the next half hour or so... Wiggle the board. Power it off and on several times. Wiggle the board some more. Re-test lots. The problem has gone.
We'll find out in a while, but techincally the most likely reason for the distorted sound seems to have gone.
So lets get back to sorting that DC filter cap out.
Remove the offending DC filter cap .
Clean the pads carefully.
Solder in the new cap.
Wire up and power on.
Test the sound with Galaga Deluxe.
It works.
Okay apply gentle pressure to the board with a soft pokey thing. No problem. Keep trying various suspect areas. No problem.
Houston I think we have working audio.
I know this is a fairly trivial fix, and it's not really complete. It could do with having all the electrolytics replaced and some more cleaning (Damn you Macro Lense). But I think we need a bit more practice with our tools.
She's now sat proudly on my desk at work (excuse the modified case, from the previous owner, I'll sort that as soon as I can find a new front bezel).
So next week maybe we should find out what's wrong with The Amiga Collector's A4000 sound.
I was a single amiga owner. My trusty 1200 and I had been through a lot together and I'd learnt a lot about modern computing from it.
My introduction on here ( https://www.amibay.com/showthread.php?t=35759 ) describes how I acquired my 1200 and some of the things I did with it. From it I learnt to program, to render, to paint, to diagram, to word process, to compose "music", to edit sound, to type (oh so many hours on IRC), to administrate, how complex multiprocessor and I/O systems worked, about multitasking, and a sort of rough idea of how it was engineered to do all the wonderful things it did.
MS-DOS and Windows PCs, even the mighty macintosh, held no interest for me.
Many years later when my good friend (from many years of Amiga related learning and fun as well as being a cool guy) gifted me his old A4000/030 I was thrilled.
For the entire life I've known this machine the sound had always been overtly distorted. I didn't care, but I did decide to look into why it didn't work at some time. After all how hard could it be to replace even the op amp if that was what was broken.
Roll forward a few more years, a house move and plenty of other changes. I get the pleasure of meeting some new Amigans at work.
One of them in particular seems to feel he missed the boat a bit due to his being 10 years my junior and is now rapidly making up for it. So he's a bit keen to poke around and I'm more than happy to assist and advise. He's currently the owner of at least a CD32, an A600, one or more A500 and recently an A4000.
Sometime during this recent time I did some research into the audio system on the A4000 and came across a great guy in New Zealand who was able to give me some pointers and great advice, both via his web site and via email.
I finally got around to taking it apart, and started cleaning it gently with IPA and a soft toothbrush, taking extreme care around some of the obvious damage.
I removed the corrosion I could see and the badly furred battery and cleaned up the amp circuitry. I then set to testing various elements and came to the conclusion it was the vref to the op amp that was at fault.
Not really having the space for any serious work on it I carried on cleaning the whole board and de-fluffing the insides, might as well preserve what I can.
Another 6 months pass.
You are in a wild forest. To the north is a dark path.
To the south is a slightly less dark path.
>
Suddenly a weekend appears, where some how the avid Amiga Collector has offered me use of his kitchen, tools and services to have a go at finding out exactly what is wrong with the audio. With it always being much nicer having a fellow Amigan at hand for ideas and assistance I wasn't going to pass up the opportunity. The kitchen, tools and skills an added bonus.
This about about how far away my eyes focus sharply.
I'm fairly skilled with a soldering iron and a multimeter, and an oscilloscope, if one is at hand (we don't have one). I can read schematics and translate them to circuits. But hell this 1206 stuff is small; and therefore scary to a good old discrete guy like me. Now I know 1206 is considered huge these days and there are bound to be guys (and hopefully gals) on here who are laughing out loud at me stating 1206 is small, but I'm hoping the general consensus will be it's scary.
On with the prOn.
So take it apart. Might as well do something fun.
The next job is read, and refresh the grey matter on simple op-amp circuits, compare schematic with board and turn it over lots.
Next job is think, apply logic and do some more reading to confirm possible theories. Think of tests that will confirm these theories.
And stare at the board some more.
So for some of the tests we're going to need it powered up, guess we need to work out what is the minimum configuration for an operational Rev B A4000.
Voila, it shows us the begging screen. One motherboard, cpu daughterboard, some chip ram, some fast ram and the all important PSU.
It does help to know which way the composite/RGB switch on the back of the monitor should be before trying this excercise.
Inspect stuff.
VIAs. Oooh grubby. We'll give them a poke later.
A damaged DC filter cap connection.
Gratuitous Amiga computer city shots.
Gratuitious Photography setup shot.
The Amiga Collector is busy reading elsewhere, so I do a bit more cleaning from the review of the macro shots. I get a thin bit of wire and poke some of the vias clean.
Okay so time to do some actual testing. After a little bit more refreshing the grey matter I work out I need to test the voltages at either end of both r401 and r402.
Hmm this meter seems to have a broken negative sign. Switch meter.
Yep definitely a problem there. The 0.45v should be 2.5v. The Amiga Collector is reading stuff elsewhere so I call him over to show him. And the problem disappears.
Over the next half hour or so... Wiggle the board. Power it off and on several times. Wiggle the board some more. Re-test lots. The problem has gone.
We'll find out in a while, but techincally the most likely reason for the distorted sound seems to have gone.
So lets get back to sorting that DC filter cap out.
Remove the offending DC filter cap .
Clean the pads carefully.
Solder in the new cap.
Wire up and power on.
Test the sound with Galaga Deluxe.
It works.
Okay apply gentle pressure to the board with a soft pokey thing. No problem. Keep trying various suspect areas. No problem.
Houston I think we have working audio.
I know this is a fairly trivial fix, and it's not really complete. It could do with having all the electrolytics replaced and some more cleaning (Damn you Macro Lense). But I think we need a bit more practice with our tools.
She's now sat proudly on my desk at work (excuse the modified case, from the previous owner, I'll sort that as soon as I can find a new front bezel).
So next week maybe we should find out what's wrong with The Amiga Collector's A4000 sound.
