A4000 emits high pitched squeal after recapping.

[sovietconscript]

got my Amiga motherboard back today after sending it out to be recapped because of a missing RCA sound channel. unfortunately after installing the board the audio problem I was having is worse, sort of. the problem of no audio from one of the channels seems to be fixed but I continually have a extremely high pitched sound coming from my speakers. when A game is playing its somewhat lessened but its still extremely noticeable. on the plus side I do now get both channels of sound but unfortunately the high pitched continuous squeal makes it unplayable. I've tried 2 separate speakers and headphones to the same effect. on one odd note. I hooked the sound up to my Amiga monitor which has the built in stereo and the squeal was significantly reduced to almost nothing. the only problem there is one audio channel in my monitor is blown out so I don't get both sound channels from it. on my speakers and headphones I tried just having the left or right RCA connected to see if it was an issue with one or the other but they both Emmit the high pitched squeal. I have no idea why the monitor does not have the issue. any ideas? are there certain speakers I need or any kind of filtering device I can use that you know of? on one more odd note. I like to test with Elite because of the Sonata music in the intro, if one sound channel is not working it sounds noticeably wrong. anyways I got both channels except for the horrible sequel over top BUT when I play Advanced elite on WHDLOAD if anyone is familiar there's a weird part before the game loads that plays a guitar sound effect and says CARE across the screen...the squeal completely goes away during this but once the game starts it the squeal is back.
the guy who did the recapping said this as a possible source but hes not an Amiga expert
"If you look at the audio circuit there is a spot where those same docs that cover the Errors in the silk screen on the cpu card, In those same doc's They talk about needing Bi-Polar caps in the audio circuit, So in those 2 spots I substituted (2) Ceramic Bi-Polar 10uf caps to make 20uf, previously there was 22uf electrolytic caps in those 2 spots."

would using Ceramics and Tantalum caps in the audio circuits instead of electrolytic caps cause this issues?

[GadgetUK]

My gut feeling is its those caps tbh. Quite why you would replace with ceramic i've got no idea... There are suppliers of the 22uF bipolar around, i've got 2 waiting to go into my 1200 when I can be bothered.

The other thing you can do is put two electrolytics around both ways in order to 'fake' the bi-polar nature. ie.

cap 1 > + -
cap 2 > - +

[Loedown]

I have no idea why you don't return the unit to be repaired properly under warranty.

I would suggest you have some accidental oscillation coming from the op amps, probable open circuit component or incorrect value.

[sovietconscript]

Originally Posted by Loedown

I have no idea why you don't return the unit to be repaired properly under warranty.

I would suggest you have some accidental oscillation coming from the op amps, probable open circuit component or incorrect value.

I didn't have a business do it. i was recommended a guy. so, no warranties. he offered to replace the caps with the original type but its going to cost me $25 min + 2 weeks just for shipping back and forth. he usually does Mac's and I suppose they use the ceramic caps.

[sovietconscript]

I checked for grounding issues but found none, removed the MB from the case and still the issue. here, i uploaded a video of the problem. turn your volume down!

[ Show youtube player ]

[Loedown]

Originally Posted by sovietconscript

I didn't have a business do it. i was recommended a guy. so, no warranties. he offered to replace the caps with the original type but its going to cost me $25 min + 2 weeks just for shipping back and forth. he usually does Mac's and I suppose they use the ceramic caps.

I would suppose they use electrolytic like most other things do or possibly sscon but besides that your audio is distorted. You need to send the board to someone who does Amiga repairs and knows Amiga computers not Apple. The Amiga audio circuit isn't hard to understand but knowing what to look for in repairing the audio is very important as usually it's a combination of capacitors and then some track rebuilding and fault finding. Does Amigakit in the USA do repairs and if so are they close to you?

[bubbob42]

I'd guess there is some more damage to the traces on the board, caused by leakage of the old caps (there often is and changing caps is not enough)

My A4k's audio circuit had to be rebuilt partly from scratch with copper wires. It has only ceramic caps now and sounds fine. Look for someone skilled in A4k board repair.

Best regards,

Marcus

[sovietconscript]

but 2 things interest me about this I was wondering if anyone can answer.

1) why when I play advanced elite when it does the guitar riff and display CARE. the high pitched noise completely goes away.

2) why do I not have the high pitched sound issue on my amiga monitor? I would be happy using the monitor if one of the RCA ports on the monitor was not dead. I've tried using only 1 RCA port when using the speakers but I always get the sound but via the monitor speaker it sounds fine (minus the missing sound effects due to one channel being dead).

[Loedown]

Originally Posted by sovietconscript

but 2 things interest me about this I was wondering if anyone can answer.

1) why when I play advanced elite when it does the guitar riff and display CARE. the high pitched noise completely goes away.

2) why do I not have the high pitched sound issue on my amiga monitor? I would be happy using the monitor if one of the RCA ports on the monitor was not dead. I've tried using only 1 RCA port when using the speakers but I always get the sound but via the monitor speaker it sounds fine (minus the missing sound effects due to one channel being dead).

Have you checked the power rails? When the video is more / less it will influence the power rails and chances are that your 'technician' has cocked up a part or done something similar, he could have placed a capacitor on the wrong place.

Just get it looked at by someone who knows what they're doing, I can't remote diagnose it without having it on my bench.

[pandy71]

Originally Posted by sovietconscript

would using Ceramics and Tantalum caps in the audio circuits instead of electrolytic caps cause this issues?

Connect Line In in your PC to Line Out on Amiga, use Audacity or any similar software to record what Amiga produce.
Play attached file on Amiga while recording.

You can record more ie few seconds before and after plying file, do not use any audio compression - provide plain wav or you can use lossless compression (for example flac).

http://www.filesplat.com/~shared-download?id=6RX240XT6OFB6B5WNHH666MHU3XVXC45

[8bitbubsy]

You could take some pictures of the audio region of the pcb to let us have a look. Maybe there's an obvious fault that is visible even from a picture!

[sovietconscript]

heres some pictures of the area

[Loedown]

One of the RCA connectors is non original, he hasn't cleaned around LF347 properly and he's done a horrible over soldering job on the capacitors. Your pictures aren't sharp enough to really discern much detail.

[sovietconscript]

does anyone know anyone in the US that I can send the Motherboard to for a complete repair?

[gnujon]

Originally Posted by GadgetUK

My gut feeling is its those caps tbh. Quite why you would replace with ceramic i've got no idea... There are suppliers of the 22uF bipolar around, i've got 2 waiting to go into my 1200 when I can be bothered.

The other thing you can do is put two electrolytics around both ways in order to 'fake' the bi-polar nature. ie.

cap 1 > + -
cap 2 > - +

Isn't one good reason to replace electrolitic caps with ceramic ones that the ceramics should last a lot longer and they won't leak out all over the board again?

[Loedown]

Originally Posted by gnujon

Isn't one good reason to replace electrolitic caps with ceramic ones that the ceramics should last a lot longer and they won't leak out all over the board again?

It's a good idea yes as they won't leak but it's still under test to see if it's a viable solution to the problem, there may be other unforeseen issues and until everything is tested 100% I won't be advising it as a viable solution.