A4000D drops volume by 75% on one channel

Hey there ppl.

Woah, It's been a long time since I was here last time.. perhaps some of you will remember me?

Well anyway.. I've come across an old A4000D with a slight fault to it's audio-out. It drops the volume on one channel to about 25%. Now I know I've seen this problem before on other machines and on the net but I can't seem to find any info on it.

If you have any ide what's gone wrong and how to fix it, let me know will you.

Oh, and if you're a master at fixing CD32's let me know, as I've got one of those that've bitten the dust as well...

[patrik]

In which way has the CD32 bit the dust?


/Patrik

[Karlos]

Sounds like a dodgy amp - I dunno if the amps are on-chip (inside paula) or off-chip. If theyre the latter, hopefully it shouldnt be too difficult to get fixed...

[SilvrDrgn]

The Op-Amps are separate.  They are not in the Paula chip.

[shIva]

the same does mine ...

@xchristofferx :

try to unplug the functioning chinch outlet. my 4000 works either on the left or on the right channel. the problem is, it doesn´ t work on both together.

@SilvrDrgn :
where can we find them ? is there a printed V xxx ?

[SilvrDrgn]

I believe they are near the stereo audio connectors on the A4000D motherboard.  I cannot be more specific than that 'cause I'm at work right now.  If you search the net for A4000D schematics, those will help you.  I have the schematics in an archive at home, but as I mentioned I'm at work right now.

[jj]

@ xchristofferx

I remeber u dude, havn't seen much off you since the site went down at the beggining of last year.

How u been keeping

[Jose]

Sure I remember you :-D Good to see you're back. I thought you were addicted with so  many posts at the time, and then had found a cure  :-P I know I haven't. People come and go, and there are only few survivors after some years.
The most ancient person I remember from amiga forums is Redrumloa from the Amiga.de forums in Jim Collas times, must be cause of his strange nick. I didn't hang around much at that time though.
No idea for your problem. You were selling a pretty  stuffed A4000 about two years ago (or was it 3? :-D ) .
What do you think of the more recent "developments"?

[z36ra]

SilvrDrgn wrote:
The Op-Amps are separate.  They are not in the Paula chip.

If it's an OP-Amp problem, I can do that.

Looks like 25W or a puller will solve the problem.

Send it to me...

[Jose]

@z36ra

Yeah, but the guy is not in US, shipping is damn expensive. I lost a bargain  A4000 once from the US,  cause shipping was more expensive than the computer!

[Castellen]

I repaired an A4000D for the same fault last week, I've seen it a few times in other machines too.
Can be caused by a number of things, but most of the cases I've seen are the SMD electrolytic capacitors leaking electrolyte onto the PCB which corrodes tracks, causes bias upsets on op-amps, etc.

The 22µF ones seem the worst, check around the base of the capacitors (the small round silver ones) for signs of discolouration or corrosion.  Sometimes the shiny soldered legs on the capacitor also turn black, indicating there is corrosion underneath.

I would not recommend trying to remove and replace these yourself unless you have good SMD soldering skills.  It's easy to lift and damage PCB tracks.
I have schematics here if you want to do some more faultfinding yourself.

Drop me an email if you need a copy.

Anthony.

Oh my.. I need to logon more often, I had forgotten the amount of traffic this site had - and still has it seems .

Well, I'm still alive and kicking . In july/august I'll get connected to a permanent highspeed ISP and from then on I'll be spending a lot more time in the forums again .

I'll be getting that "broken" A4000 in less than a week or so and hopefully I'll be able to repair it and rebuild a nice new PPC setup once again. I was such an idiot to sell it all of back in 2001 . The A1200T I got instead is just crap compared to the trusty A4000.

For those interested - I'll be posting more about the CD32 in a while ...


Anyway, back on topic. It seems as if the problem with the volume can be resolved - that's great news . But, I'm not exactly a master of the art of soldering and could use some help from someone local (sweden?), or really detaled instructions on how to get things done, I'm not all thumbs .

You'd make me a very happy man if you would waist some time on helping me out. You know, it's good carma and stuff . Both Castelan & SilverDrgn seem to know a lot about these things?


If you feel that you're up to it, please, send me an email at: xchristofferx'AT'c64.org

Thank you for all the replys. See you all later.

[z36ra]

xchristofferx wrote:
Oh my.. I need to logon more often, I had forgotten the amount of traffic this site had - and still has it seems .

Yes you do.

So far... I can solder but am in USA and can do OP-Amps and Capacitors. Would need to see the machine to diagnose but would be too expensive.

Next. I think the problem is in the capacitors and thats even easier to repair but I don't have schematics on that machine... tracing is easy in this case negating the need for them, but again I'm in the USA.

I think your best bet is selling the mobo on ebay and buying a new one. make sure you tell the buyer that it has a problem. It will bring you less money but honesty is the best policy.

[SilvrDrgn]

I just got a problem like this fixed on my A4000D motherboard over the weekend.
The capacitors on my board have been replaced by the non-polarized type.
However, upon putting everything back together, the sound on my A4000 was still
terrible.  After 7.5 hours of messing around with the hardware (different
motherboard, accelerator, removing expansion cards, removing Zorro expansion
daughter board), my dealer and I found the problem.  It was as simple as the
-12 volt and it associated ground wire not making proper contact in the main
6-pin motherboard power connector.  When I plugged that in after the capacitor
change, the -12 volt and its ground got pushed out of the connector somehow so
they weren't making contact.  The op-amps (operational amplifiers) that produce
sound on the Amiga require -12 and its ground in order to function properly.
Without either one, the sound output is very bad.  We connected the main power
connector and then wiggled and pushed in the wires with a pair of needle-nosed
pliers.  After that, perfect sound from my system!