Author Topic: 6128 sound issue with some tunes/demo/games  (Read 584 times)

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Offline jpx13

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6128 sound issue with some tunes/demo/games
« on: 19:49, 18 June 17 »
Hello !

It seems my 6128 has a strange fault related to music playing... :(

I noticed that fault while looking the awesome Batman Forever demo and the 30 years Demo: some instruments sound seems really distorted/high pitched. I compared with the same music in Winape, and all was nice and "musically OK"  ;D

To investigate further, I made tests with some other demos, and with some chiptunes. It was half the time right, with a melodious sound, but sometime the sound seems distorted, and not always on the same channel.

I made some tests in basic, using the Sound, Env and Ent basic commands, and everything went fine on the 3 channels !  :o

I then downloaded Starkos, and tried to narrow the fault listenning to some tunes, and creating my own instruments. It seems that the problem is tied to the use of "hard enveloppe" as it is called in Starkos. When the tune uses an instrument of a square form or with noise, everything is as it is supposed to be, but when there is a "hard enveloppe" used, the sound is distorted and high pitched, as in the demos/games I tried before.

Does this mean the AY of my 6128 is half/partly dead or dying ?

I already ordered a new chip, comming from the slow boat from China, but before replacing it, I thought perhaps someone has an idea, or an explanation.

Thanks in advance,

JP

Offline jpx13

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Re: 6128 sound issue with some tunes/demo/games
« Reply #1 on: 09:45, 25 June 17 »
Hello !

A bit of an update today... I found the problem seems to be related to temperature. Today the weather is cloudy, and the temperature less warm than the last days (I live in south of France, and temperature was well above 30°  ;D ).

I just tried a chiptune which is causing the issue on channel 2, and for nearly 4 or 5 minutes, the sound was normal ! After that delay, it became again high pitched and sounded more like a buzzing whine than the sort of "string bass" it was before.

Any thoughts ? Is it definitely my AY that has gone bad ? The one I orderered hasn't arrived yet (the slow boat IS slow, yes...)

Do you think it is possible to test with the new AY without removing the old one, by just cutting the +5V leg of the old AY and piggybacking the new one on top of the old ?

JP

Offline Bryce

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Re: 6128 sound issue with some tunes/demo/games
« Reply #2 on: 10:54, 26 June 17 »
Have you inspected the solder joints to the AY. It may be a dry joint.

Regarding AY testing: No, you can't piggyback the AY to test it, the original AY will still have an effect on the new AY even when it's not powered.

Bryce.

Offline jpx13

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Re: 6128 sound issue with some tunes/demo/games
« Reply #3 on: 21:18, 26 June 17 »
hello Bryce,

You are right,I will inspect the solder joints of the AY, I must remove the PCB anyway if I have to replace it... As it is temperature related, it could be something like that.

My hope to test the AY by piggybacking the new one are now gone away  ;D

Thank you for your help,

JP

Offline jpx13

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Re: 6128 sound issue with some tunes/demo/games
« Reply #4 on: 11:18, 01 April 18 »
Hello,

A late update on this topic... I've been busy for the last months, and just managed to take out  the Mobo of my 6128...

I desoldered the AY, and put a socket.

I then placed my new AY, marked GI AY 3-8912, and when I fired up the machine, I discovered that the sound is now OK, but the keyboard is faulty, with random chars when pressing keys (it was hard to type run"disc !!)

So my "not A" type AY should be a "A" type.

When I put back the desoldered AY, same as before, issue with the sound, but keyboard fine !!

What I think I will do is soldering pullup resistors, and it should do the trick !

JP

Offline jpx13

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Re: 6128 sound issue with some tunes/demo/games
« Reply #5 on: 19:24, 01 April 18 »
And it's now working !

I just soldered a resistor array (8x 47k was the only one I found laying around) and it seems to work as it should.

I knew the resistor array should be 8x 2.2k, but decided I could try the one I had and despite the huge difference regarding the values, it is working fine !

So if someone as this same problem with an AY, and can't find the right chip, or is sent the wrong one from china  :(   the soldering of the resistor array (located near the AY chip) is a working solution.

Have a nice day !

JP