Please help I have a strange Issue, Don't know what to do.

steve nicholl · 03:05, 13 July 15

My 464 unfortunately seems to have almost given up on audio after 31 years of service. I have never asked for help with a machine in my life and although embarrassed to ask for help with this, I'm will for my dear Amstrad. So far:
1: I have checked all solder joints\connections\traces\caps and as far as I can see, they are good.
2: I have checked its function and booting up\loading games\tape audio are working (so CPU,PPU,40007,RAM,CRTC and gate array should be fine)
3: I have checked all keyboard functions and they are good (so surely AY chip is ok)
I am unsure how to test if it is caused by internal amp failure (IC301, IC302), could this be the cause? Also unsure if the 74LS145 could cause this. I have attached a short phone vid detailing the problem.
The only other thing that I can think of in the last few days was that while at work my nephew was over at my place, as he does, to play some pc\console. The cpc was running a game at this time and I had a in progress project pad (sega 6 btn controller) that was only partially wired internally which was sitting on the floor next to the Amstrad. If he plugged this in to "have a go", would an internal short have caused this sound failure as a I know that the AY chip has something to do with the joystick inputs. He says he didn't plug it in, although it was moved when I got home and cpc was turned off (and he's 6!).
Any help on this is unbelievably appreciated. Thank you for your time.

Bryce · 08:41, 13 July 15

Hi Steve,
It sounds like your nephew may have poked something into the internal speaker of the CPC and possibly torn the membrane. Have you tested the sound from the sound out port at the back?

Bryce.

steve nicholl · 13:36, 13 July 15

Thanks for getting back to me. I'm just returned from work there now and replied asap. As far as the speaker goes, that's the thing I don't understand. I have another PC speaker attached to the solder points on the opposite side of the pcb, so there are now 2 speakers both doing the same thing (stereo output port puts out nothing). This is why I feel that it could be an amplification problem and the speakers are not being "driven". I have a background in vehicle audio systems and my gut tells me that the speakers are not getting enough power, amperage, amplification or whatever it would be technically termed in this case. I just don't have any background or knowledge of microcomputer logarithmic sound outputs and how the signals "work". Is there an internal amp or is the volume control a function of the logarithmic output of the PSG chip? If it is internal amp then surely it can be probed for output and voltage would\should increase with amplification. Or maybe its something simple and I'm a fool! I just don't know. Any thought appreciated.

Bryce · 13:46, 13 July 15

The Audio port on the 464 is connected directly (via a few resistors) to the AY, no amplifier involved. So if you're getting nothing here, then the AY has probably died. You'll need to connect active speakers to this port to hear anything.
Adding a second speaker in parallel won't tell you anything if the original speaker is shorted, you need to disconnect the original speaker first to eliminate that as the problem, then try the Audio port with active speakers.

Bryce.

steve nicholl · 14:03, 13 July 15

Will do. I'll remove all system speakers, try again with audio out port and report back. Thank you so very much.

Bryce · 14:07, 13 July 15

Just pull the connector that goes to the tape deck, this disconnects both the speaker and its amplifier. If the Audio Port still doesn't work then the AY is damaged. If sound comes out then either the amplifier or the speaker is damaged.

Bryce.

steve nicholl · 15:02, 13 July 15

Ok, I'm being stupid.
I disconnected the system speaker in case of a short and connected a 3.5mm jack to the audio out which I fed to my Sony amp. I am getting the same clicking\crackly sound from speakers that was coming from internal speaker.
I have read your comment and tried to understand how to "pull the connector that goes to tape deck". I assume that this is the 8 pin on the motherboard, but if I do that then I cannot power on the 464 to test the sound output from the audio port. Do you mean jumper pins on the motherboard so that I power it that way and then hold del for example to test port? Sorry that I'm being thick here. Mine is the 1st cut down board, the MC0044D if it makes any difference.

Bryce · 15:13, 13 July 15

Oops, Yes, you'd have to jumper the power after disconnecting the 8pin connector. As I usually directly power PCBs that I'm repairing I forgot to mention that

In that case you'll need to disconnect just the sound cable from the 8pin connector. That's pin7 (pin 6 should be empty) and the wire is usually white. This will disconnect the Amp and you should have a direct connection from the AY to your Sony Amp. If this is still just "giving clicks" then you need to swap the AY.

Bryce.

steve nicholl · 16:02, 13 July 15

Okay, I disconnected the white audio wire (pin 6 had a blue wire + there were no empty pins just for info) and.............nothing, not even the clicks. My AY is dead as far as sound goes then.
I notice looking at the service manual that pin 2 of IC102 (between the vcc and analog channel outputs) is marked as TEST 1. Can I use this to confirm? Also the I\O ports go through this chip I see, so I must assume that the connected controller has indeed shorted voltage through a pin which was not intended for a positive charge and damaged it causing the sound issues. The keyboard side of things and everything else for that matter (assuming I'm correct that the keyboard matrix runs through this chip) are fine strangely. So, do I have any options with this. Are AY chips obtainable or is there an alternative. I am quite capable of replacing an IC but I would be willing to consider any alternative (bar, playing the music out of my stereo in the background, hoho!). Can not thank you enough for your efforts as I am making really good progress here. (Just heard, R.I.P Satoru Iwata)

||C|-|E|| · 16:09, 13 July 15

If you need to replace the chip maybe it is time to put a socket where it used to be and then, in case something happens again, you will not need to desolder and solder anymore. I wish they would have put sockets everywhere... the good news is that the AY is easy to obtain (as far I know). Is this guy, right?

AY-3-8912A General Instruments DIP-28 Integrated Circuit from UK Seller | eBay

steve nicholl · 17:10, 13 July 15

Seriously! That inexpensive! Amazing news if that's all it will take to fix my beloved cpc. Could you confirm that this chip is the correct one for my version of board (my chip reads AY-3-8912 from Microchip Taiwan, I assume they are all the same + didn't spectrum +2's use it or something)and I will order immediately with an appropriate socket. Amazing help, never seen anything like it on any forum. Thanks again.

gerald · 18:16, 13 July 15

Most CPC are fitted with a AY-3-8912.
If you replace it with a AY-3-8912A you need to add pullup on the keyboard lines, but the MC0044 (in fact none of the 464) doesn't have a footprint on the PCB to solder them.

steve nicholl · 18:41, 13 July 15

That's typical, I've ordered one. So check for the chip is std non-a variant. Will start looking and report back. Ta.

Bryce · 21:25, 13 July 15

I'm sure I've some here. Send me a PM and I can organise one for you. I probably have a socket too (which is advisable).

Bryce.

TFM · 21:35, 13 July 15

Oh yes. To put in a socket is very much advisable.

steve nicholl · 22:22, 13 July 15

I seem to have found a non-A variant of the chip for £4, so... winner! A socket is on its way as well for a massive £1 and both should be here by Thursday at the latest. I will post results as soon as I know. Thank you Bryce for your kind offer and I may take you up on it yet. Yet again guys, Fantastic job with all your help, you are all absolute stars as this would have taken me weeks on my own. Talk soon.

||C|-|E|| · 23:39, 13 July 15

Good luck with everything!

steve nicholl · 02:08, 18 July 15

Okay guys, I have been testing while waiting for the parts as the chip has arrived but socket hasn't as yet. All that seems to be a bit irrelevant though as I have partly found the issue. It's not the chip apparently, but something to do with the keyboard membrane I think.
I was testing the traces with the multimeter from key contact to key contact which were all good. I then tested from the very last contact on the membrane (furthest from connector ribbon) to contact point on ribbon end. I found that on the 5th row down there is no contact registering after a distance greater than * icon. On 4th row there was no register of contact beyond the @ key. I suspected that the lines were bad after this, but were "good enough" for a short key to key contact beep check so I hadn't noticed.
I decided to clean them, rebuild and try the keys at the end of the lines as I was sure that they were working before and yes they worked ok. BUT!!!! When checking the keys I pressed the down arrow key as it was one of the "end row" keys and heard a beep! Upon loading Treasure Island Dizzy, I found that I still get the quiet crack, crack sound, but if I hold down the down arrow key FULL SOUND IS RESTORED PERFECTLY!!!??!?!?!
What is going on? Are bad tracks causing the "faulty track" keys to short through other keys and still work while messing up the sound? I'm kinda confused now, so do I need a membrane or huh? Any help\thoughts\ideas are very very welcome!

gerald · 09:11, 18 July 15

Quote from: steve nicholl on 02:08, 18 July 15
Okay guys, I have been testing while waiting for the parts as the chip has arrived but socket hasn't as yet. All that seems to be a bit irrelevant though as I have partly found the issue. It's not the chip apparently, but something to do with the keyboard membrane I think.
I was testing the traces with the multimeter from key contact to key contact which were all good. I then tested from the very last contact on the membrane (furthest from connector ribbon) to contact point on ribbon end. I found that on the 5th row down there is no contact registering after a distance greater than * icon. On 4th row there was no register of contact beyond the @ key. I suspected that the lines were bad after this, but were "good enough" for a short key to key contact beep check so I hadn't noticed.
I decided to clean them, rebuild and try the keys at the end of the lines as I was sure that they were working before and yes they worked ok. BUT!!!! When checking the keys I pressed the down arrow key as it was one of the "end row" keys and heard a beep! Upon loading Treasure Island Dizzy, I found that I still get the quiet crack, crack sound, but if I hold down the down arrow key FULL SOUND IS RESTORED PERFECTLY!!!??!?!?!
What is going on? Are bad tracks causing the "faulty track" keys to short through other keys and still work while messing up the sound? I'm kinda confused now, so do I need a membrane or huh? Any help\thoughts\ideas are very very welcome!

As far as I remember, sound working only when a key is pressed is a side effect of a failing AY, not the other way

steve nicholl · 13:16, 18 July 15

Ah I see, Okay. I now understand as, if you follow me, the problem not making sense makes sense now. There was no logical reason mechanically that I could think of that would cause this odd situation.

If this is a symptom, then I understand that when the key is pressed, it is correcting the sound "inside the IC" rather than in the membrane or board. As soon as this socket arrives I'll swap and let you know. Thanks millions!

arnoldemu · 17:45, 18 July 15

I would be interested with what happens if you run these two tests:

keyb allows you to press the keys on the keyboard, interesting if the i/o part of the psg has been broken.

psg.dsk runs a load of audio tests, so you'll need to listen, I hope it doesn't drive you crazy.
All kinds of tests, volume, envelope, tone, noise etc.

the sample ones are not written yet.

News:

Please help I have a strange Issue, Don't know what to do.