A4000 Audio Problem

[spaceman88]

Hi,
A couple of months ago I posted a question about my newly aquired A4000's right mouse button not bringing down the top menu (the keyboard equivalent would, right amiga + Alt). I got some suggestions, but didn't get a chance to seriously work on  it until today. Someone asked me about the sound, when I checked it was terrible (low, static). The funny thing is it gets about five times louder (according to my ocsilloscope) when I press the otherwise useless right mouse button!! I downloaded the audio test program from the excellent Amiga Technical Resource guide. I measured some voltages on U402, my +12v & -12v are OK but the VREF on pins 10 & 12 are too high at 4.1 - 4.2v. I checked the resistance between pins 13-14 and pins 8-9 and got about 770 ohms. The output on pin 8 is only about 120mV (when the mouse button is pushed) and is clipped on the bottom. I used to do surface mount repairs on Super Nintendos 10 years ago, but no longer have the hot air soldering system, so I hope this doesn't get too involved :-). Any ideas what to check next?
Thanks, Len

[da9000]

Hi Len,

without much thinking about it (the mouse troubles complicate the matter), but my first guess is that you've got to do this anyways, since it'll save your A4000 in the future, but primarily because of the broken sound:

http://amiga.serveftp.net/audio_repair.html

Smell the SMD caps to see if there's a nasty odor. That'll be a good indicator.

And while you're at it, perhaps this could be a possible job for you too:

http://amiga.serveftp.net/A3640_capacitor.html

Both should be easy for you, given your background with surface mount repairs on SNES systems. Of course you might be 70 years old by now and have shaky hands (I hope not!) in which case get some helping hands as some areas are tight and lifting pads is common. I've done both jobs on many Amigas, so I can always help if need be (I'm in the US though, don't know how far).

Good luck

[spaceman88]

Well I'm not quite 70 yet (46), but the eyes are not quite as good as they were. This was an Ebay special (works fine, but sold as is!!) When I first received it I didn't check it well enough and even left positive feedback!!! I bought this with the idea of building a Video Toaster setup, but now I just want my sound back :-(. I had found the audio repair site before and was using it to trace through the circuit. This unit has a 68030 so I won't have to worry about the A3640 problem. There doesn't seem to be any odour and I would hate to change all the audio parts and find out that Paula is bad. I may try the audio fix without hot air but NOT Paula!
Len

[da9000]

Hey Len,

I would not recommend using a heat-gun for the SMD caps. It's not very hard to do it with a decent soldering iron, and less chance of screwing something else up. Plus there's a decent number of them (if you want to do them all), so it'll be much quicker with the soldering iron, than having to cover all the areas needed to blast with the heat-gun.

As for Paula, what Anthony means in his site is that if there are signs of battery leakage or whatnot, then remove/replace. If you don't have such a problem I would do 4 things:

1) remove and re-seat Paula and see what happens

2) if no improvement, get another Paula, try it

3) if no improvement, perhaps add solder to the pins/holes of the Paula socket, from the back-side of the motherboard, and see what happens

4) if no improvement, start with the audio-circuitry SMD caps. I use tantalums for replacement because I don't want to bother with SMDs when I'm your age :-)

Good luck!

[spaceman88]

Hi again,
Unfortunatly Paula doesn't have a socket on my board (Rev. C), it's soldered (with VERY small legs) directly to the board.
Thanks, Len

[da9000]

Ah. Well, skip to the SMD caps then :-)

Like Anthony says, these chips don't damage so easily.

Has the battery leaked at all?


EDIT:
I've not tried this with any custom chips, but it works for DRAMs: you can piggy back another chip on top of the faulty one, so you can temporarily test to see if the new one makes a difference and thus isolate the problem. It'll be tricky with Paula or anything such, with so many pins and everything on it. DRAMs with 10-20 pins are much easier.

[Kin-Hell]

DP....soz....

[Kin-Hell]

Sounds to me like you have a CIA chip problem. There are 2 of them, both surface mounted. Plugging devices into the Mouse & or joystick ports is NOT good practise when your Amiga is running. Same goes for Keyboard, Paralell/serial ports. Just don't do it when the Miggy running. Try another known working mouse to eliminate your mouse being faulty.

I've also seen boards with battery leakage just trash the entire board as far back as the Sound chips & rear ports. This damage isn't always evident untill you spray the board with an Alcohol based cleaning agent. What sometimes appears to be a small amount of leakage around the battery area can be more sinister than what you can actually see. Brake Cleaner for cars will work, but better to use any evapourating alcohol based Electrical cleaner. For spraying & hanging the board to dry, the "Fur" & discolouration to the PCB just shows the consequences of battery leakage.

Assuming you have no battery damage to the board & to resolve these symptoms you are experiencing, I'd do the following.

1) Try another known working mouse. If Right mouse button has the same symtoms, move on.

2) Ground yourself correctly & remove the board from the Case. Lay the board on a solid surface with some anti-static material under the board. Look very very closely at all the Capacitors & SMD Resistors on the board. Ruptured Capacitor tops & or a sweaty "morning-dew" look means they are fux0rd & need replacing. Look for this sweaty look on any of the boards components & be sure you have a good clean & bright light over the board while you do this. If none of this is evident, try pressing down firmly but gently all the socketed Chips to reseat, then retry the miggy.

3) At this point, if the symtoms are still there, you need to get hold of JJB @ Amiga France & he should be able to repair it for you. As far as I am aware, he replaces the surface mounted CIA's with socketed items, thereby making it easier for home users to pull the CIA's & replace them very easily using a PLCC Puller. I have managed to lever socketed Chips without a puller, but it's not for the faint hearted. You have a very very high risk of splitting the socket when you dont use a PLCC Chip removal tool. I only mention this because by pressing on the chips, you may expose another problem & end up with a Green screen when firing the Miggy up again. One reason for doing away with sockets in the first place, but repair costs for surface mounted stuff is high & very specialised.

Best of luck with your diagnostics.

Kin    :-)

*Edit   I can't emphasise the Importance of you being Earthed whilst doing investigation work like this. 1 nanosecond & you could have more problems than you originally started with!  You mention use of an ocsilloscope above so I'm guessing you already know this, but assumption is the Mother of All F**k-Up's! ;-)

[spaceman88]

Hi guys,
I should have mentioned that I tried another mouse, what really bugs me is that the sound gets louder when the RMB is pushed. The battery was removed before I got it so I don't know how bad any leakage was.
Len

[da9000]

Len, you can try some of Kin's suggestions, because as I recall last time I had this same problem with the right mouse button, it turned out to be the cable of my mouse.

Still, the audio is almost definitely SMD caps. And as far as battery clean up, water with just a drop of non-polar detergent should do the job. For an in-depth discussion: http://68kmla.net/forums/viewtopic.php?t=2381&start=25

EDIT:
As for battery leakage, you can look around the board and see if you spot any corrosion on the copper tracks or any thin green tint on various component legs. If you do, those are signs of it happening. Obviously the worse signs will probably be where the battery was (unless this machine had a Lithium coin-cell, in which case no leakage)

[spaceman88]

Hi Guys,
Thanks for all the info. I'll reread the posts a few times and order some caps & do a little cleaning. If I get desperate enough maybe I'll part it out on Ebay!! :-).
Len

[da9000]

BTW, and again, excuse me if I'm reiterating stuff you probably already know, what I do sometimes to test things (while waiting for the parts to come) is I rip off some broken hardware some axial/radial capacitors with equivalent ratings, and use those temporarily to see if the problem is fixed. Then I remove them and put the finalized components (in my case the tantalum 'tear drop' ones, which I got from jameco.com, in case you're looking for a source - if you need parts numbers, let me know as well)

Good luck with the project!

[spaceman88]

Yes, I tried bypassing some of the audio caps with no improvement (this method works quite well troubleshooting some circuits, like vertical output sections of T.V.s or monitors). If you have the part #'s handy ...:-). BTW I turned the computer on a couple of times yesterday and both times the sound was good and the right mouse button worked for 2-3 minutes. Then the sound slowly faded, became distorted (bottom of the sine wave clipped) and the RMB stopped working. I tried cooling Paula and some audio parts with freeze spray, but no effect. I'm going remove the main board and clean it as suggested by Kin-Hell and in the link you provided. then we'll see what happens.
Thanks, Len

[countzero]

your audio circuitry caps are leaking. I've seen these symptoms on three different a4000 boards, two of them which died on me cause I was late to act. third one I could save by timely replacement of all SMD caps. As far as I understand, these caps are at the end of their life and should be replaced ASAP when you get a a4000. There's no way around it. And it's not that difficult. I could finish a whole board in about an hour after getting used to it and have the parts ready (and I should mention I'm not tech wizrd).

[beller]

I agree with countzero, you've got caps about to fail.  

My A4000's sound was failing along with the failure of the par: port.  I sent it to JJ at Amiga Center France and he fixed both problems which were, apparently, related.  Working fine now and I had him put in a coin style battery too...

Bob