Left sound channel on A1200 gone - Page 2

Shadowfire · 29 September 2009, 01:23

Can you please tell me which capacitor you are referring to? Specifically what is the silkscreen designation (the white letter/numbers on the board)?

Based on your description of the meter, it sounds more like you're measuring an inductor than a capacitor, in which case the designator starts with L, not C, and the behavior you are seeing is correct.

8bitbubsy · 29 September 2009, 01:25

kipper2k: Found it

Quote:

Originally Posted by Shadowfire

Can you please tell me which capacitor you are referring to?

C235 (100µF SMD), under the RF and the power connector.

UPDATE: I tried to measure between pin 1 of U15 to C324, they make good contact (beep!)... Same with pin 7 and C334 (right channel cap).

kipper2k · 29 September 2009, 01:40

Quote:

Originally Posted by 8bitbubsy

kipper2k: Found it

C235 (100µF SMD), under the RF and the power connector.

UPDATE: I tried to measure between pin 1 of U15 to C324, they make good contact (beep!)... Same with pin 7 and C334 (right channel cap).

K, that shows that the traces is good to the Caps. you can run a jumper from the +ve side of your right channel cap to the +ve side of your left channel cap. If the sound level is equal to both channels then it is possible that Paula is bad

edit... ok, i confess, i actually did fry one channel of a Paula chip (left channel) one time, not sure how, but i did end up swapping Paula out. (symptons were very similar to this)

8bitbubsy · 29 September 2009, 01:42

Quote:

Originally Posted by kipper2k

K, that shows that the traces is good to the Caps. you can run a jumper from the +ve side of your right channel cap to the +ve side of your left channel cap. If the sound level is equal to both channels then it is possible that Paula is bad

What do you mean by +ve? The + pads?

kipper2k · 29 September 2009, 01:48

Quote:

Originally Posted by 8bitbubsy

What do you mean by +ve? The + pads?

The electrolytic caps you removed are polarity conscious, ie have a positive and negative terminal. Look on the motherboard for the position of the + sign and that will show you which side is +ve (positive)

8bitbubsy · 29 September 2009, 01:53

Quote:

Originally Posted by kipper2k

The electrolytic caps you removed are polarity conscious, ie have a positive and negative terminal. Look on the motherboard for the position of the + sign and that will show you which side is +ve (positive)

Okay..

Safe to jumper them with kynar wire? Just need to be sure

kipper2k · 29 September 2009, 01:57

Quote:

Originally Posted by 8bitbubsy

Okay..

Safe to jumper them with kynar wire? Just need to be sure

yup, just be careful you dont short anything

8bitbubsy · 29 September 2009, 02:04

Ok, I bridged both the + pads on C324 and C334...
This is horrible, all I hear is a NOISY and low sound in the right channel.. BUT I hear both the channels in the right channel

kipper2k · 29 September 2009, 02:16

hmmm, i,m not sure whats going on there. did you follow Zetr0's suggestion and remove, clean and resolder the caps ?. when you remove the caps, get a magnifying glass or a good camera with macro and take a good look at the board and traces, if you changed all caps then it may be time to revisit them (check they aint on backward etc)

rkauer · 29 September 2009, 02:16

Fried Paula.......

8bitbubsy · 29 September 2009, 02:19

kipper2k:
None of the caps are backwards, and all the traces looks fine...

UPDATE: All seems good :/ Tried to resolder some that looked bad soldered, didn't help...
I start to think that the left non-polarized cap is dead...

kipper2k · 29 September 2009, 04:03

Quote:

Originally Posted by 8bitbubsy

kipper2k:
None of the caps are backwards, and all the traces looks fine...

UPDATE: All seems good :/ Tried to resolder some that looked bad soldered, didn't help...
I start to think that the left non-polarized cap is dead...

You have a few options left to try before thinking the worst that one channel of Paula is fried (It is an easy IC to fry).

Remove the right channel Cap, solder it to the left channel, see if your sound level increases and sounds normal. if it does, solder a new cap to the right channel and see what the sound is like. if its good then youre a lucky man!.. if not...

check for solder bridges or blobs of solder that may have accidentally fell on the board, (seen that a few times) if all is good and still not working then its time i think to do as everyone is saying and replace Paula. I think there are probably a lot of people who have a few spares here and there that are willing to help

8bitbubsy · 29 September 2009, 04:17

Okay, I almost give up... I resoldered all the caps and did a superb job, excellent soldered, not too much solder, etc etc... Everything looks wonderful. However, each time I boot my miggy, I get the green screen O' death (chipram error). Spent many minutes seeking the board for solder blobs, bad soldering etc... Couldn't find ANYTHING

Second A1200 down. Hurray, I'm so lucky.

EDIT: o_O The Indivision AGA 1200 is causing the green screen.. Without it, it boots fine.. Tried to resocket it many times, no luck.....
EDIT2: Nevermind, it works good now... Now to testing the right cap to the left!

kipper2k · 29 September 2009, 04:37

There is a fix for the indivision. If you have the HP chip the indivision has a hard time staying on the chip so a little sanding and glue etc normally cures the stubborn fit ones.

Did you swap over caps on the audio channels ?

Don't trash your A1200 boards, if you cant fix them then someone else could fix it for you. I dont mind helping but i think shipping costs here to Canada would make it too expensive a repair

8bitbubsy · 29 September 2009, 04:50

Tried it now, still no sound in the left channel

(I never trash Amiga hardware)

Shadowfire · 29 September 2009, 07:06

C235 is a coupling capacitor for audio from the conexant video encoder to the RF modulator. Are you getting audio from the RF modulator, or the RCA jacks? It appears to be a mono, mixed signal from the audio circuitry.

C235 should *not* drop down to 1 ohm. It is internally shorted, and should be replaced. This would definitely cause level clipping and maybe buzzing in your RF modulator audio, though, since the audio is no longer being correctly coupled between stages.

Since the audio in only 1 channel is out, though, this can't be your problem (although it is an issue and should be replaced if you ever want RF output with sound).

The easy way to troubleshoot this would be with an oscilloscope and a looping sample of a set frequency playing on both channels. Since you have one known good channel, you compare waveforms at the same spot on each channel until they differ, and it typically narrows the problem down to 3 or 4 components.

You could do much the same thing by comparing AC & DC voltages relative to audio ground, if you have a decent multimeter.

Play a stereo tone as above. Compare measurements at the following areas, relative to audio ground:
Left Channel/Right Channel [notes] (probable cause)
U3.34/U3.33 (failed Paula)
U15.14/U15.8 (bad U15, C321 or C331)
U15.1/U15.7 (bad U15, C322, C323, C332, or C333)
R324/R334 [test the side which connects with C324/C334] (bad C324/C334)

8bitbubsy · 29 September 2009, 19:09

Thanks for the info

I don't use RF, I've removed the RF module itself (I did this long long ago)...
I don't have any decent multimeter (got a cheap one) nor oscillator :/ I'll "debug" more later today.

8bitbubsy · 29 September 2009, 23:04

(Posting another one to bump!)

Where can I find the 44-pin A1200 paula schematics? I found one, but it was *very* messy (the Commodore one)... Any pics or so which tells what pins are what on paula? Then I can try to directly connect the "audio left out" to my receiver and turn the volume all up to see if the channel works..

Any parts I can skip, so I can directly solder a wire from paula to the output cap or so..? I never use the sound filter anyways!

prowler · 29 September 2009, 23:21

Hi bubsy,

I've uploaded a PDF of the A1200 Schematics for you.

Paula is on page 9. It looks as if you require pins 33 (Right) and 34 (Left).

8bitbubsy · 29 September 2009, 23:26

That's the one I had, heh.. Okay, pin 33 and 34... Now to count the pins to get there!
EDIT:

Can't find it!

Which pin is 33 and 34?
And where should I borrow GND from?

29 September 2009, 02:19	#31
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	kipper2k: None of the caps are backwards, and all the traces looks fine... UPDATE: All seems good :/ Tried to resolder some that looked bad soldered, didn't help... I start to think that the left non-polarized cap is dead... Last edited by 8bitbubsy; 29 September 2009 at 02:57.

29 September 2009, 04:17	#33
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	Okay, I almost give up... I resoldered all the caps and did a superb job, excellent soldered, not too much solder, etc etc... Everything looks wonderful. However, each time I boot my miggy, I get the green screen O' death (chipram error). Spent many minutes seeking the board for solder blobs, bad soldering etc... Couldn't find ANYTHING Second A1200 down. Hurray, I'm so lucky. EDIT: o_O The Indivision AGA 1200 is causing the green screen.. Without it, it boots fine.. Tried to resocket it many times, no luck..... EDIT2: Nevermind, it works good now... Now to testing the right cap to the left! Last edited by 8bitbubsy; 29 September 2009 at 04:35.

29 September 2009, 23:26	#40
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	That's the one I had, heh.. Okay, pin 33 and 34... Now to count the pins to get there! EDIT: Can't find it! Which pin is 33 and 34? And where should I borrow GND from? Last edited by 8bitbubsy; 30 September 2009 at 00:16.

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29 September 2009, 01:23	#21
Shadowfire Registered User Join Date: Aug 2001 Location: Connecticut USA Posts: 617	Can you please tell me which capacitor you are referring to? Specifically what is the silkscreen designation (the white letter/numbers on the board)? Based on your description of the meter, it sounds more like you're measuring an inductor than a capacitor, in which case the designator starts with L, not C, and the behavior you are seeing is correct.

29 September 2009, 02:04	#28
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	Ok, I bridged both the + pads on C324 and C334... This is horrible, all I hear is a NOISY and low sound in the right channel.. BUT I hear both the channels in the right channel

29 September 2009, 02:16	#29
kipper2k Registered User Join Date: Sep 2006 Location: Thunder Bay, Canada Posts: 4,323	hmmm, i,m not sure whats going on there. did you follow Zetr0's suggestion and remove, clean and resolder the caps ?. when you remove the caps, get a magnifying glass or a good camera with macro and take a good look at the board and traces, if you changed all caps then it may be time to revisit them (check they aint on backward etc)

29 September 2009, 02:16	#30
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	Fried Paula.......

29 September 2009, 04:37	#34
kipper2k Registered User Join Date: Sep 2006 Location: Thunder Bay, Canada Posts: 4,323	There is a fix for the indivision. If you have the HP chip the indivision has a hard time staying on the chip so a little sanding and glue etc normally cures the stubborn fit ones. Did you swap over caps on the audio channels ? Don't trash your A1200 boards, if you cant fix them then someone else could fix it for you. I dont mind helping but i think shipping costs here to Canada would make it too expensive a repair

29 September 2009, 04:50	#35
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	Tried it now, still no sound in the left channel (I never trash Amiga hardware)

29 September 2009, 07:06	#36
Shadowfire Registered User Join Date: Aug 2001 Location: Connecticut USA Posts: 617	C235 is a coupling capacitor for audio from the conexant video encoder to the RF modulator. Are you getting audio from the RF modulator, or the RCA jacks? It appears to be a mono, mixed signal from the audio circuitry. C235 should not drop down to 1 ohm. It is internally shorted, and should be replaced. This would definitely cause level clipping and maybe buzzing in your RF modulator audio, though, since the audio is no longer being correctly coupled between stages. Since the audio in only 1 channel is out, though, this can't be your problem (although it is an issue and should be replaced if you ever want RF output with sound). The easy way to troubleshoot this would be with an oscilloscope and a looping sample of a set frequency playing on both channels. Since you have one known good channel, you compare waveforms at the same spot on each channel until they differ, and it typically narrows the problem down to 3 or 4 components. You could do much the same thing by comparing AC & DC voltages relative to audio ground, if you have a decent multimeter. Play a stereo tone as above. Compare measurements at the following areas, relative to audio ground: Left Channel/Right Channel [notes] (probable cause) U3.34/U3.33 (failed Paula) U15.14/U15.8 (bad U15, C321 or C331) U15.1/U15.7 (bad U15, C322, C323, C332, or C333) R324/R334 [test the side which connects with C324/C334] (bad C324/C334)

29 September 2009, 19:09	#37
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	Thanks for the info I don't use RF, I've removed the RF module itself (I did this long long ago)... I don't have any decent multimeter (got a cheap one) nor oscillator :/ I'll "debug" more later today.

29 September 2009, 23:04	#38
8bitbubsy Registered User Join Date: Sep 2009 Location: Norway Posts: 1,710	(Posting another one to bump!) Where can I find the 44-pin A1200 paula schematics? I found one, but it was very messy (the Commodore one)... Any pics or so which tells what pins are what on paula? Then I can try to directly connect the "audio left out" to my receiver and turn the volume all up to see if the channel works.. Any parts I can skip, so I can directly solder a wire from paula to the output cap or so..? I never use the sound filter anyways!

29 September 2009, 23:21	#39
prowler Global Moderator Join Date: Aug 2008 Location: Sidcup, England Posts: 10,300	Hi bubsy, I've uploaded a PDF of the A1200 Schematics for you. Paula is on page 9. It looks as if you require pins 33 (Right) and 34 (Left).

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