6128 AY-3-8912A ? Works in CPC 6128 ?

Started by willow3411, 19:58, 14 February 22

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willow3411

Hello,
My AY-3-8912 sound chipset from my CPC 6128 no longer works (no sound but the keyboard works fine). I can't find component 8912 anymore. we only find AY-3-8912A . but does it work? because pin two is not the same (not connected to A). Can adapt the 8912A on the CPC 6128? thanks in advance Willow

eto

Unfortunately I don't know if there is any difference. Actually I wasn't even able to find a datasheet for the A variant.

But maybe this helps. Seems it is in stock.
https://amigastore.eu/715-ay-3-8912-sound-generator-chip.html

willow3411

Thank you ! I also saw the link to order but I'm afraid it's A. on pin A #2 is not connected. on 8912 it is the TEST function. I have an A and it does not work on CPC 6128 (the keyboard does anything)

Nworc

The pin 2 is just a test pin and is irrelevant.

The difference between the 8912 and 8912A is that the latter does not have the internal pull up resistors on the output port. While the sound will work, the difference in the pull up resistors will interfere with the keyboard logic in the regular CPCs. Of course it is possible to work around this but that requires some soldering. I would prefer to buy the right type, which is much less effort. This is no theory, I've checked that with a test board.

willow3411

Oh yes ! welding does not scare me if you have a tutorial or explanation I am a taker thank you

Nworc

#5
Ooops, what did I do   :o

Well, it's not that complicated, I mean?  You would just add the pull-up resistors externally.  The question is just: what value should they have.  I just don't know - you would have to experiment.  Maybe that information can be found in the specs of the non-A type if you find it, or somewhere in the service manual of the CPC.

However, I must express my displeasure at the fact that people here are obviously toying with the idea of tinkering with a historical cultural asset by means of a quick and dirty repair. I cannot endorse this!  :picard:

TotO

#6
Hello,

The AY-3-8912/A has the same pinout, but it require to add an extenal resistor network at the proper place on the CPC 6128 mainboard to allow the keyboard and joystick to work properly.


EDIT: You can use a 2k2 resistor network. It is not dirty to do it, Amstrad does.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

willow3411

Quote from: Nworc on 21:58, 14 February 22
Ooops, what did I do   :o

Well, it's not that complicated, I mean?  You would just add the pull-up resistors externally.  The question is just: what value should they have.  I just don't know - you would have to experiment.  Maybe that information can be found in the specs of the non-A type if you find it, or somewhere in the service manual of the CPC.

However, I must express my displeasure at the fact that people here are obviously toying with the idea of tinkering with a historical cultural asset by means of a quick and dirty repair. I cannot endorse this!  :picard:
thank you very much The problem is not dirty repair, but the fact that I can't find AY-3-8912 on the market anymore. Suppliers only deliver 8912A

willow3411

Quote from: TotO on 22:01, 14 February 22Hello,

The AY-3-8912/A has the same pinout, but it require to add an extenal resistor network at the proper place on the CPC 6128 mainboard to allow the keyboard and joystick to work properly.
Ben precisely, that I understood well, and it is this diagram which I would like to find with the values ​​of the resistances.
Thanks

TotO

And a picture to show that. 2K2 works fine and you just have to put it on the good way.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

willow3411

#10
Very good job !!!
But the way ? I don't look....
thanks

TotO

#11
Here where is located the common of the 9pin (8+1) resistor network.
Before you ask, there is probably a white dot on it to know the good pin. :)
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

Nworc

Quote from: willow3411
Quote from: Nworc
However, I must express my displeasure at the fact that people here are obviously toying with the idea of tinkering with a historical cultural asset by means of a quick and dirty repair. I cannot endorse this!  :picard:

thank you very much The problem is not dirty repair, but the fact that I can't find AY-3-8912 on the market anymore. Suppliers only deliver 8912A

Sorry, my humour might be a bit too dry to get noticed   ;D

willow3411

Quote from: Nworc on 23:58, 14 February 22
thank you very much The problem is not dirty repair, but the fact that I can't find AY-3-8912 on the market anymore. Suppliers only deliver 8912A

Sorry, my humour might be a bit too dry to get noticed   ;D
Everyone has their own sense of humor Don't worry, it takes more than that to upset me. :)

willow3411

Quote from: TotO on 22:47, 14 February 22
Here where is located the common of the 9pin (8+1) resistor network.
Before you ask, there is probably a white dot on it to know the good pin. :)
sorry, I had not seen well :). on my map it was a bit hidden. Do you know where I can find this component? thanks in advance

willow3411


TotO

"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

willow3411


willow3411

Quote from: TotO on 15:12, 15 February 22
Yes, the one printed 2K2 is OK.
Goodnight all . A little background on the repair. A huge thank you to all of you (especially TotO). Everything works perfectly with the network of 2.2K resistors. On the other hand Attention: Amigastore.eu supposedly sells AY-3-8912 but they are copies (made in taiwan) and they do not work!! thanks again here are the photos

TotO

Great!  :)
Next time, think to order some sockets!  ;D
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

willow3411

Quote from: TotO on 20:26, 18 February 22Next time, think to order some sockets
Yes the supports are on order but still late in France!!!

TotO

It was faster that I send you one.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

Nworc

Quote from: willow3411
On the other hand Attention: Amigastore.eu supposedly sells AY-3-8912 but they are copies (made in taiwan) and they do not work!!

Excuse me, I cannot believe that this is a "bad copy". What I see on the photo is a genuine chip made by General Instruments, produced in Taiwan. Taiwan is not China, Taiwan has a high tech industry comparable to South Korea. I suspect that your keyboard is not working, and that's why you say the chip is not working.

If you wish, you can send me the chip to check what's wrong. I think it's just a simple issue with the pull-up resistors. I mean, does anyone here know for sure what the correct value for the resistors is? The CPC keyboard logic is very picky in this, sometimes it stops working if I make an angry face ...

TotO

#23
Well... If the IC do not works, he can ask to be replaced. (it is wrote 2 years warranty)
Now, I will not take the defense of sites selling circuits 5 to 10 times the price they buy them.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

eto

Quote from: TotO on 11:20, 19 February 22Now, I will not take the defense of sites selling circuits 5 to 10 times the price they buy them.

Is there any other place where you can buy them for less than that? Even on Aliexpress I have to pay more than 20€ + shipping + taxes/customs. 


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