Left sound channel on A1200 gone

[8bitbubsy]

I recapped my A1200 rev 1D.4 with all new SMD caps (didn't change the through-hole ones), and exchanged the two sound caps with non-polarized ones... Now I only get sound in the right channel! I checked the solder connections like 25 times, and the polarity of the other SMD caps too...

Looks to me like the sound error is in the other caps somewhere, what caps should I check? The two non-polarized ones under the sound RCAs are already checked...

[Zetr0]

@8bitbubsy

time to get mr multimeter out m8-

firstly I would check if there is a ground issue with the left audio, then check before the cap, replace the cap if need be you may have a dud..

[8bitbubsy]

Originally Posted by Zetr0

@8bitbubsy

time to get mr multimeter out m8-

firstly I would check if there is a ground issue with the left audio, then check before the cap, replace the cap if need be you may have a dud..

I spent like an hour trying to check the traces with the multimeter, it beeped a lot, which means the connections seems fine... Checked the two point on each the non-polarized caps...

I really think that the issue lies in the other SMD caps, but I don't want to spend one hour on each of them - therefore I ask: Does someone know which of the SMD caps (except the two under the RCAs) that's for the sound circuit?

[Shadowfire]

Take your multimeter and set it to resistance and put the leads across each cap.
It should start off with a low value and then increase to a few K or more.
If it starts low & doesn't move, that means there is a solder short, probably under the cap.

[8bitbubsy]

Originally Posted by Shadowfire

Take your multimeter and set it to resistance and put the leads across each cap.
It should start off with a low value and then increase to a few K or more.
If it starts low & doesn't move, that means there is a solder short, probably under the cap.

Thanks, this did the job!
Measured all the caps, they went from low to higher.. EXCEPT one cap, that didn't react at all - I guess it didn't get contact, I'll try to resolder it and tell you how it goes.

[8bitbubsy]

The cap makes the multimeter beep once, then it shows 1419 quickly, and goes down to 1... This is the ONLY cap (polarized) doing this! Is it destroyed? It was brand new
No matter what pin I put - and + on, it does this... Weird! Tried to desolder it and measure as well, same...

[prowler]

Originally Posted by 8bitbubsy

The cap makes the multimeter beep once, then it shows 1419 quickly, and goes down to 1... This is the ONLY cap (polarized) doing this! Is it destroyed? It was brand new

When you are testing polarized capacitors with a testmeter, always put the red probe (+) on the capacitor lead marked '+'. This will avoid injecting a reverse-polarity voltage at that point on the Amiga's motherboard.

If you have done everything correctly, then the capacitor is useless. This is not unknown with new capacitors. All it takes is poor QA.

[8bitbubsy]

Originally Posted by prowler

When you are testing polarized capacitors with a testmeter, always put the red probe (+) on the capacitor lead marked '+'. This will avoid injecting a reverse-polarity voltage at that point on the Amiga's motherboard.

If you have done everything correctly, then the capacitor is useless. This is not unknown with new capacitors. All it takes is poor QA.

Okay, I see :P Time to grab one from my broken A1200 mobo then (measure it first!)

EDIT: Still same, it measures like 1400, then fast down to 1 : ... I did still exchange it - no sound in the left channel still

[rkauer]

Small value capacitors will do this. They charge pretty fast.

[prowler]

Originally Posted by 8bitbubsy

The cap makes the multimeter beep once, then it shows 1419 quickly, and goes down to 1... This is the ONLY cap (polarized) doing this! Is it destroyed? It was brand new
No matter what pin I put - and + on, it does this... Weird! Tried to desolder it and measure as well, same...

Originally Posted by 8bitbubsy

Okay, I see :P Time to grab one from my broken A1200 mobo then (measure it first!)

EDIT: Still same, it measures like 1400, then fast down to 1 : ... I did still exchange it - no sound in the left channel still

If this was "the ONLY cap (polarized) doing this", then surely the equivalent component that you replaced in the right audio channel was not doing it.

Perhaps the one that you grabbed from your broken A1200 actually has the same fault.

[8bitbubsy]

Originally Posted by prowler

If this was "the ONLY cap (polarized) doing this", then surely the equivalent component that you replaced in the right audio channel was not doing it.

Perhaps the one that you grabbed from your broken A1200 actually has the same fault.

Don't think so :/ The other A1200 mobo did have sound in both the channels, and I used the same cap from the same place...
The A1200 have been playing a cracktro for like an hour now, it works very good, except for the lack of sound in the left channel.

[coze]

check 1200 schematics and find paula raw outputs. solder some wires there and see if you got sound. from there check the routes till it gets to audio filter. eventually you'll find where it goes off.

[prowler]

Originally Posted by 8bitbubsy

Don't think so :/

But, if that was the ONLY cap doing it, then the other one (on the other channel) can't possibly have been the same when you tested them!

[8bitbubsy]

If I unplug the right RCA, I get sound in the left RCA! But only the right channel's sound, heh.. So that means that that problem is lying a bit before the filter/amplifier, I guess....

[prowler]

Is that sound in the left channel all the time, but it's drowned out when the right channel is connected so you can't hear it?

[Zetr0]

@8bitbubsy

you have a groudning out on the audio circuit...

at this point I would pull all the caps, clean up and start again.... check at each stage m8.

[8bitbubsy]

Originally Posted by prowler

Is that sound in the left channel all the time, but it's drowned out when the right channel is connected so you can't hear it?

Yep! But if you only have an RCA in the left RCA, paula switches to mono mode, so I'm not sure if the left channel is working or not - all I hear is the right channel in it
Sounds like the issue is very early after the paula chip

EDIT: When both RCAs are in, the sound in the right is high. If I unplug the left RCA, the sound in the right is getting lower o.O
EDIT2: If I plug in my 030 acc, all I get is a blank screen... Seems like the caps are important for several things

[kipper2k]

I had a similar problem, with the problem i had was the trace from the left channel capacitor runs underneath the right channel cap. The caps leaked and wrecked that trace.

to check you can run a jumper wire from pin 1, U15 to the +ve input of C324 (the left channel cap. (pin 7, U15 goes to right channel cap)

If when you run the jumper you hear the sound coming out and both channels sound equally loud then you will know that there is an open wire between U15 and the cap


Edit... Be careful, shorting out this chip when attaching a jumper can destroy Paula!!

[8bitbubsy]

Originally Posted by kipper2k

I had a similar problem, with the problem i had was the trace from the left channel capacitor runs underneath the right channel cap. The caps leaked and wrecked that trace.

to check you can run a jumper wire from pin 1, U15 to the +ve input of C324 (the left channel cap. (pin 7, U15 goes to right channel cap)

If when you run the jumper you hear the sound coming out and both channels sound equally loud then you will know that there is an open wire between U15 and the cap


Edit... Be careful, shorting out this chip when attaching a jumper can destroy Paula!!

Where the F*** is U15? I've looked a bit, can't find it...

[kipper2k]

Originally Posted by 8bitbubsy

Where the F*** is U15? I've looked a bit, can't find it...

oh poop.... my apologies... you are talking about the 1200... Lemme look at the a1200 schematics

sorry


edit... K. the A1200 still uses U15, i'll locate it on the board for you... Rev 1D has it but i cant locate it on my Rev 2B ? thay must have made changes to the board