Requiring technical diagnosis : my CPC can't play music anymore !

[qbert]

Hello,

After 30 years of (near) continuous usage, it appears my CPC464 has finally met its first hardware failure. 

It appears the sound part is damaged some way. Whereas it still can produce low bass sound correctly, all acute and medium sounds are now missing. Per moment, some distorded sound is produced in place of regular acute instrument, but it is quite sparse.

No, my own ears are not responsible for this  : i checked the same musics using my PC.

If first thought the (very old) internal speaker was in cause, but I connected a pair of amplified speakers to the audio out connector : the result is exactly the same. Now, each music on the Amstrad sounds just like a piece of crap ! 

Does anybody here have ever encountered a similar faillure in the past ? Is it possible that the AY-3-8910 may be in cause ? Or perhaps a discrete component for signal amplification : a (near) dead capacitor or what ?

Any hardware expert here ?

S.O.S : Save Our Souls !!! 

[Bryce]

Most likely culprit is the AY. The audio out only involves a few additional resistors, so when that's not working the AY is definitely the problem.

Bryce.

[qbert]

Thank you very much Bryce, I was hardly envisionning exploring the schematics by myself. 

So, the first test I have to plan consists in changing the AY.  By the way, Bryce... is it socketed  or soldered  ?




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[Bryce]

Unless it has been changed before it will definitely be soldered. How's your soldering skills?

Bryce.

[qbert]

Unless it has been changed before it will definitely be soldered. How's your soldering skills?

Bryce.

That means I have to rape my first ever CPC with a burning iron
raaaaaaaaaaah eugghhhhhhhhhhhhhhh ghghghghghghghgh... 

...

have I made me explicit ?

[Bryce]

You can send it to me if you prefer.

Bryce.

[qbert]

You're a gentleman, Bryce.

However, I bought last year a (german) soldering station specially in the idea I would have to repair something.

But of course, I was not expecting my first "patient" would be my most beloved piece of hardware ever ! 

I suspect chip desoldering to be quite rough as you have to pull over the chip with a clamp, even after having removed the solder.

My fear is to damage another part while doing this : how to keep the whole board tidy on my desktop while working on a part of it ?
Bryce, do you have any special workbench or whatever for working on large PCBs or do you rest it directly over your desktop, while soldering ?

[dxs]

No you don't have to pull on the chip. Doing so almost certainly will destroy tracks or solder pads (especially if you're not the soldering guru).
Actually removing some Ic is real easy. Cut all the pins just where they join the plastic body. Now heat each pin one by one while very gently pulling it with pliers. When the solder has melted the pin comes easily so no force is needed and none should be used.
Obvious drawback: the Ic is trashed. Which is fine when removing a dead or cheap part.
Then solder wick is what you need to clean old solder. Alternatively the vacuum sucker thing works great especially on double sided boards like the CPC mainboard.
Altogether a 5 minute job and risk free with some habit. You can practice on dead pc motherboard or whatever.

[qbert]

Thank you dxs for your guidance.
I own both the (manual) vacuum sucker and the solder wick, despite being little succesful with desoldering in the past (I only had a low-cost 40W iron and it simply did'nt work on professionally soldered PCBs !).

However, I'm not yet convinced the AY is the faulty part : I have to proceed a bit with my tests, for the moment.
In the meantime, any new idea concerning the diagnosis procedure is welcome. 

[gerald]

However, I'm not yet convinced the AY is the faulty part : I have to proceed a bit with my tests, for the moment.
In the meantime, any new idea concerning the diagnosis procedure is welcome. 

The only other culprit could be the PPI (8255), which interface the AY to the Z80.

[Bryce]

I'd recommend using this method to remove the IC: IC Repair - CPCWiki   especially if it's the first IC you've ever removed and the PCB is precious to you.

It could be the 8255, but they tend to be more robust than the AY and a damaged 8255 would probably also give keyboard errors at the same time as they share the same bus.

Bryce.

[qbert]

Great doc, @Bryce ! I would never have guessed that point (until it was too late) :

Now we need to remove each pin from the PCB. This should ONLY be done from the TOP of the PCB! Heating the joint from the bottom of the PCB will result in broken tracks on the top side if you pull the pin before it has reached the right temperature! [...]

@Gerald : thank you. I'll also track the shematics for any capacitor between the 8255 and the AY.

[gerald]

@Gerald : thank you. I'll track the shematics for any capacitor between the 8255 and the AY.

It's all direct connections, only wires.
As Bryce said, it is more likely that the AY is faulty than the PPI.

[TFM]

That brings me to an idea: We could use the PlayCity for Sound diagnosis! I'll add this to my mile long 2DO list...