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Old 03 October 2006, 19:34   #1
sjurmr
 
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A1200 sound problem

I recently bought myself a used A1200 and is somewhat disappointed with the sound. Like two of my earlier A500's, the sound is horrible and very distorted. In accordance, the internal floppy drive doesn't seem to work.
From what I remember from the "early days" both I/O and sound is controlled by the Paula-chip. Does this indicate that my Paula might be blown? In that case, is replacement my only option?
I should mention that an external drive and internal HD works fine.

Any advice is appreciated.

Regards,
Sjur
 
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Old 03 October 2006, 21:41   #2
voxel
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Hi :-)

it seems you A1200 suffer from the leaking capacitor syndrom :-(

There is two caps in the sound output that was meant to be non polarized that commodore replaced by normal polarized ones to gain some cents...

it leak after some times and destroy the pcb around, the sound is ugglyer as time passes.

the only thing to do is repairing the mobo, recreate the dead traces on it (and some are in the inner layers of the mobo), replace the caps with non polarized ones and all is good again :-)

that's a lot of job and have to be done by a good professional. ask JJ www.amigacenter.com :-)
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Old 03 October 2006, 22:25   #3
BippyM
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or get another mobo for about 5 (12 eoro maybe)
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Old 04 October 2006, 20:39   #4
sjurmr
 
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Thanks guys. Have looked both on ebay and the eab marketplace for a motherboard but the cheapest one I found was 13 on ebay. Any tips on where to find a cheaper one (5 would be nice )

Regards,
Sjur
 
Old 06 August 2013, 21:39   #5
kipper2k
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I am just going to resurrect this thread. I just got a couple of A1200's and the first one (and i believe the second one also) has a very high level of distorted sound on both channels. The volume level is higher than a normal a1200 so i will try to see what is going on. The floppy drive is also intermittent as well so i believe that Paula may be to blame. there is a lot of green residue left around Paula so i am expecting to find Paula is bad. A cleaning of the area with isopropyl did nothing.

The board was actually recapped in 2011 by Amigakit so i assume that it was working back then.

Quote:
Originally Posted by bippym View Post
or get another mobo for about 5 (12 eoro maybe)
Haha, Those days are gone
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Old 06 August 2013, 22:18   #6
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k, I fixed it, didn't have to remove Paula. It was a very simple fix(es). I'll post pictures later
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Old 06 August 2013, 22:47   #7
jimbob
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Kipper strikes again

Are they by any chance rev1A MBs? I see you fixed it but was going to suggest you take a look at this -

[ Show youtube player ]
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Old 06 August 2013, 22:57   #8
kipper2k
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Quote:
Originally Posted by jimbob View Post
Kipper strikes again

Are they by any chance rev1A MBs? I see you fixed it but was going to suggest you take a look at this -

[ Show youtube player ]
It was a 1D4, had the correct resistors in there (680 ohm) but my digital camera found the problem. Wish i'd have seen this video first though
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Old 07 August 2013, 16:53   #9
kipper2k
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Here is a picture of the cause of the audio problem. I took some close ups to see if there was anything obvious that i could see and when i looked at this area i found the problem.




Before reading on, see if you can see the problem...

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The left channel feedback resistor to the Op Amp had snapped in half and as a result there was no feedback to the Amp causing the Amp to go to maximum gain which caused the left channel to go full bore causing distortion. I replaced the resistor with same value resistor (680 ohm) and sound is now perfect.

The problem i had with the floppy drive which caused me to think that Paula was bad was actually caused by a cold solder joint on the floppy 4 pin connector. I resoldered the 5v pin and all is fine.

edit, one final note. The 1D4 motherboard has a 10 pin header for the mouse. You would think that Commodore would have followed the same pinout as everyone else, but NO, attaching a 9pin DB connector with the 10 pin header does not work. because the pinout is different. I had to make a custom cable as i didn't have the original one for this motherboard.

Last edited by kipper2k; 07 August 2013 at 16:59.
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