Amstrad CPC 6128 sound problems.

[Ace]

I have a 6128 which had the well known drive belt issue, that I replaced it and the drive works fine again.

The problem now is that something related to the sound goes wrong and it appears generally like one channel of AY-3-8912 malfunctions. Depending on the game, gives loud static noise, wrong pitch or no sound at all. In very few games, like commando, it gives correct sound.

In two games so far, it gives wrong behavior, unrelated to sound, like Prohibition which starts initially in-game, without the start menu and with infinite lives (!) and Renegade which doesn't go past the start menu and the CPC locks.

The above behaviors are not random and they happen exactly the same way, every time I load the games.

I tested with external speakers with the same result.

The question is: there is defective some resistor, capacitor or (I hope not) the AY-3-8912 itself and how can I test it? (Or should I throw it to the garbage? - My soldering and electronic repairs experience and knowledge is next to none!)

[Bryce]

Hi Ace,
      unfortunately it's unlikely to be a resistor or a capacitor. It could be the 8255 PIO or the AY. Difficult to say from your description. Dodgy capacitors would give random crashes, not repeatable as you describe. Obviously those two games are using some feature of the 8255 or AY that doesn't work any more. But both are repairable. Where are you and the CPC located?

Bryce.

[Ace]

Thanks for the reply!

Mine and my Amstrad's location is Greece...

[Bryce]

Hmm, a bit far to send just for a repair. Have you any local hardware people that could test the board for you?

Bryce.

[Ace]

...I think not.

I have considered replace the AY myself with those that I found at ebay:

http://search.eim.ebay.gr/?kw=ay-3-8912&ect=&elc=1&eb=%CE%91%CE%BD%CE%B1%CE%B6%CE%AE%CF%84%CE%B7%CF%83%CE%B7

...but I can't be sure that is the AY to blame and I have no experience on soldering (...and I don't want my first attempt to be a chip replacement on CPC's PCB).

Edit: ...and where can I find a 8255 PIO?

[Bryce]

Well you can use a socket, to make sure the new AY isn't killed by your soldering, but I still wouldn't recommend it as a first attempt at soldering.

Bryce.

[00WReX]

Hello,

I also have a 6128 that has a sound issue...I think it is something to do with the AY chip.

http://www.cpcwiki.eu/forum/applications/software-to-test-hardware/

I have since done some very basic testing that narrowed it down...to the portion of sound that goes missing !!

For the first five minutes or so that the CPC is on the sound is fine, so it appears to be heat related (it is consistent).

What I found was that entering the following...
sound 1,0 to 255 I would get no sound (after the warmup period)...If I put a timer in to produce a constant tone, after around 5 minutes it starts to break up then nothing.
Everything else appears OK.

sound 1,256 to 4095 is OK
sound 2,0 to 4095 & sound 3,0 to 4095 is OK

Cheers,
Shane

[Bryce]

Have you checked whether there are any dodgy solder joints on the AY or it's capacitor? I'd try resoldering them all first and re-run the test.

Bryce.