Hi!
Lately I've been "fighting" against a cpc6128plus, trying to repair some issues.
The issue I'm working now is about sound. One of the channels didn't work. On cpc plus, one of the channels goes to one of the "pseudo" stereo channels, and the other two goes to the other one. Testing the board, I didn't found anything weird so I decided to replace the sound chip.
The sound chip on cpc is used also for the keyboard, so if the chip is dead, no sound and no keyboard.
Well, last week I purchased a AY38912A/P chip. I believed it should work since the pin out is quite the same compared to the one used on en cpc plus, the AY38912/P, only one pin is different (test/no connect)
Well, carefully I remove the the AY38912/P, then I install a socket and with multimether I see that all the tracks survived, nothing was broken during the desoldering process. Now, testing.
- I place the new AY38912A/P chip on the socket: keyboard doesnt works and an also I've got horrible noise sound on the tv-set speakers.
- I place its original AY38912/P: the horrible noise dissappears but now the keyboard doesnt works
I supose that the original AY38912/P was completly killed during the desoldering.
Now, the questions:
- should I try find an original AY38912/P? is it compatible with AY38912A/P?
Thanks!
Because the "A" version require an external 2K2 resistor network to pull-up the GPIO pins.
On CPC there is the room for it. I don't know about PLUS.
EDIT: It doesn't have. You require to add it from pin 7 to 14 and took VCC from pin 3 or a closer source. (like capacitor pin)
Best to add from the Amstrad PLUS PCB back to be more easy to solder it. (or use a not "A" IC)
That sounds less like the AY was broken (since you can hear all three channels) and more like the mixer path for the centre channel is broken at some point. That's through R165 (to the left channel) and R166 (to the right). Whichever side is the one you can only hear one channel in is the one you need to look at.
Hi! first of all, thank you very much for you answers!
Quote from: TotO on 00:14, 13 January 20
Because the "A" version require an external 2K2 resistor network to pull-up the GPIO pins.
On CPC there is the room for it. I don't know about PLUS.
EDIT: It doesn't have. You require to add it from pin 7 to 14 and took VCC from pin 3 or a closer source. (like capacitor pin)
Best to add from the Amstrad PLUS PCB back to be more easy to solder it. (or use a not "A" IC)
I've got enough soldering skills for that, but maybe I preffear getting a not A chip. Does anyone knows where to get one with guarantee that it is not a chinesse reprinted fake?
Quote from: pelrun on 02:24, 13 January 20
That sounds less like the AY was broken (since you can hear all three channels) and more like the mixer path for the centre channel is broken at some point. That's through R165 (to the left channel) and R166 (to the right). Whichever side is the one you can only hear one channel in is the one you need to look at.
Well, back then I couldn't hear all three channels, only 2. But now I listen nothing, so now I supose that the original AY is really dead since keyboard doesn't works (before removing the original AY keyboard worked perfectly) Anyway, if its the resistor, that would be my first time seeing a broken resistor, weird weird weird ;-)
By the way, you said its R165 and R166, but can't find those on the board. The higher number was R98, but I did find near de AY R66 and R65. Are those what you wanted to say? wich kind of resistors are those?
Also, maybe I should mention it, before all this I changed all electrolytic capacitors since two of them were dead and computer didn't started up before.
https://www.ebay.de/itm/AY-3-8912-SOUND-CHIP-GENERAL-INSTRUMENT/283441064745
Bryce.
I can send you one to test and you will let me know if it is OK. ;D
If yes, will be kind to send me next the A version in exchange.
Hi again
Quote from: Bryce on 11:01, 13 January 20
https://www.ebay.de/itm/AY-3-8912-SOUND-CHIP-GENERAL-INSTRUMENT/283441064745 (https://www.ebay.de/itm/AY-3-8912-SOUND-CHIP-GENERAL-INSTRUMENT/283441064745)
Bryce.
Just now I purchased it. Lets see what happens!
Its supposed that the manufacturer its not important. I mean, no matter if it is from Microchip or from GI...
Quote from: TotO on 11:09, 13 January 20
I can send you one to test and you will let me know if it is OK. ;D
If yes, will be kind to send me next the A version in exchange.
Aaaargh!, I was too fast purchasing the chip! :-(
Anyway, do you know if it works or I do have to test it?
If I'm able to repair this, I'm planning on purchase some cheap chips from china and test them now that I've got the AY socketed.
Since its ebay: "doesnt works -> f**k you seller, works? I can offer them to people with same problems.
The time to search the IC and took the picture... But, if you was OK to buy a old AY IC for 15€ + 6.5€ shipping, may be it was first better for you to add over the "A" chip a 5cts resistor network to see if it fix the issue. ;D
Quote from: TotO on 11:17, 13 January 20
The time to search the IC and took the picture... But, if you was OK to buy a old AY IC for 15€ + 6.5€ shipping, may be it was first better for you to add over the "A" chip a 5cts resistor network to see if it fix the issue. ;D
Yes, thats another possibility I dont want to refuse completly, but my priority now is fully repair the computer and then make tests about it. If I add the resistors and something is not ok because I make a mistake, everything will become more confusing :-(
Quote from: makinavaja on 11:23, 13 January 20my priority now is fully repair the computer and then make tests about it. If I add the resistors and something is not ok because I make a mistake, everything will become more confusing :-(
Sure, I understand. Now, you will got an IC for testing.
Yesterday I received the chip, and I still have the same result: no keyboard and no sound.
Also, with both chips (the original and the one I purchased) if I leave the computer on for a while, automatically burning rubber will start with a qualifying race.
Any idea?
Burning Rubber does Autostart if you don't press any button, so that's normal.
If there's still no sound or keyboard, you need to investigate if the AY is getting all the signals it requires, starting with the 5V power rail and clock signal. Do you have the equipment to check these?
Bryce.
Quote from: Bryce on 14:50, 21 January 20
If there's still no sound or keyboard, you need to investigate if the AY is getting all the signals it requires, starting with the 5V power rail and clock signal. Do you have the equipment to check these?
Bryce.
I only have a multimeter, So the only stuff I can investigate is the 5V
5v tested: 4.6v arrive. The clock signal, dont know it :(
4.6V is too low, the chip will stop working at anything below 4.75V. You need to find out why it's so low. Check if it is still 4.6V when the AY is removed from the socket.
Bryce.
Sorry, a mistake writing:
4.3V, not 4.6, so its even less!
And also, the same result with the chip removed. Anyway, I'm not using the original monitor, Ii dont have it, instead I use an external power supply that works withouth issues on the other cpc6128plus board I have.
Then something close or connected to the AY has an internal short. Unfortunately, the most likely culprit is the ASIC.One final test you could do is check whether the sound works (ie: Let burning rubber start) if the keyboard is completely disconnected.
Bryce.
Tested burning rubber with the keyboard disconnected: no sound :(
Then there's a very high possibility that the ASIC is no longer doing its job. Unfortunate, as this part isn't replaceable.
Bryce.
Argh! :-(
Anyway, thank you everybody for your help then.
It curious, because before removing the original AY, at least the keyboard and two audio channels worked, but after that... could the ASIC die from that?
Quote from: Bryce on 15:58, 21 January 20
Then there's a very high possibility that the ASIC is no longer doing its job. Unfortunate, as this part isn't replaceable.
Or just the power switch that need a good cleanup ;) @makinavaja (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1919) can you test this CPC using the keyboard/power switch of your other plus ?
Hi!
Quote from: gerald on 19:21, 21 January 20
Or just the power switch that need a good cleanup ;) @makinavaja (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1919) can you test this CPC using the keyboard/power switch of your other plus ?
Yes I can, tomorrow I will try it.
By the way, how can a power switch affect the AY, the keyboard or the asic?
Quote from: gerald on 19:21, 21 January 20
Or just the power switch that need a good cleanup ;) @makinavaja (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1919) can you test this CPC using the keyboard/power switch of your other plus ?
If it was just the power switch, then it would be very unlikely that Burning Rubber would run. That would mean that every chip on the PCB was getting enough voltage, but the AY wasn't??
Bryce.
Quote from: Bryce on 08:24, 22 January 20
If it was just the power switch, then it would be very unlikely that Burning Rubber would run. That would mean that every chip on the PCB was getting enough voltage, but the AY wasn't??
For an other thread about supply for GX4000, I've bee testing one down to 4V : sound is the first thing to fail.
Knowing that the measured supply on the AY is about 4.3V on this plus and the other one is fully working, if the supply provided is indeed 5V, the power switch is one of the possible culprit for the voltage drop.
Interesting, I've never tested what parts stop functioning first if you start to dial down the voltage. I would have expected the parts that use the most current (CPU, CRTC, GA) to fail first.
@makinavaja (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1919): The reason why the switch can have an effect is because when it gets dirty or oxidised it becomes a resistor. So the more current the computer is pulling, the higher the voltage drop across the switch will be.
Bryce.
Hi!
Quote from: gerald on 19:21, 21 January 20
Or just the power switch that need a good cleanup ;) @makinavaja (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1919) can you test this CPC using the keyboard/power switch of your other plus ?
I got the same results :-(
Quote from: Bryce on 09:11, 22 January 20
@makinavaja (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1919): The reason why the switch can have an effect is because when it gets dirty or oxidised it becomes a resistor. So the more current the computer is pulling, the higher the voltage drop across the switch will be.
Thanks for the explanation!
Those ASIC chips are a pain in the ass. On MSX, the 95% of the computers uses MSX-engine chips for multifunction purposes like sound, cpu , signals.... and of course there are no chip over there for purchase.
Sh**t, so, this computer is dead, I supose u_u;
Also, I tested this too: I configured the powersupply to give 6V. Then, the AY received 5,4V and, also, no sound no keyboard.
Quote from: gerald on 09:05, 22 January 20
For an other thread about supply for GX4000, I've bee testing one down to 4V : sound is the first thing to fail.
Knowing that the measured supply on the AY is about 4.3V on this plus and the other one is fully working, if the supply provided is indeed 5V, the power switch is one of the possible culprit for the voltage drop.
Quote from: makinavaja on 15:35, 22 January 20
Also, I tested this too: I configured the powersupply to give 6V. Then, the AY received 5,4V and, also, no sound no keyboard.
That was a dangerous move. 6V is enough to fry many of the other chips, but without additional test equipment there is not much else you can do now other than declare it dead.
Bryce.
Hi All
Has anybody tried to Reflow the solder on the gate array with a a hot air gun ? ?
Hopefully yours
Ray
Quote from: Audronic on 12:35, 23 January 20
Hi All
Has anybody tried to Reflow the solder on the gate array with a a hot air gun ? ?
Hopefully yours
Ray
Why would you use a hot air gun on a through hole part? A soldering iron is the correct tool to do that.
Bryce.
Hi Bryce
" Has anybody tried to Reflow the solder on the gate array with a a hot air gun ? ?"
The GATE ARRAY the one with nearly 200 pins IC101 AMS40489 or equivalent.
Thats what I was referring to ? ?
Ray
That would be the ASIC.
? See Photo ?
Hold your horses.
If you take a look at the Wikipedia page for Gate Array, it defines them as:
QuoteA gate array is an approach to the design and manufacture of application-specific integrated circuits (ASICs) using a prefabricated chip with components that are later interconnected into logic devices (e.g. NAND gates, flip-flops, etc.) according to a custom order by adding metal interconnect layers in the factory.
Now, for the sake of communication, the naming convention around those chips has been the following (taken from our wiki):
QuoteAmstrad Custom chips
The Amstrad CPC used one custom chip: the video Gate Array (also called VGA – no connection with the Video PC standard).
Latter CPC cost down series included a "pre-ASIC"-called ASIC to merge the VGA and the CRTC.
The Amstrad Plus included a "second heart" simply referred as the ASIC.
CPC+ ASIC's part number is 40489
So you are right that the part is named Gate Array in the service manual. But it is a type of ASIC. So it is confusing. That's why it's easier to use Gate Array for the 40007, 40008 and 40010, Pre-ASIC for the 40226 and ASIC for the 40489.
Quote from: Audronic on 00:13, 24 January 20
? See Photo ?
Yes, I see a photo of the ASIC, not a Gate Array :) . But now that we know which chip is meant, my suggestion would however still be the same. A hot air gun puts too much heat into the body of the chip before it has heated the pins sufficiently. Going around the pins with a soldering iron would still be a safer solution. Yes, I've done this on occasions when the solder looked particularly dry and cracked, but it was rarely (if ever) the solution to the problem.
Bryce.
Hmmnn
Hi again everybody
If I manage to get an oscilloscope, would anybody help me saying wich kind of tests do I have to do and wich results will I get?
I never used one before and I plan getting one of those mini oscilloscopes available on internet shops. I supose with this I will learn the basics.
Another option was asking anybody to ship him/her the board (paying, of course) to see if it can be reapaired withouth touching the ASIC.
I'm quite stubborn with this kind of stuff, as I wont ever get quiet until something broked isn't fixed. Repair repair and repair before purchasing another one...
Before you go and buy one of those mini oscilloscopes, let us know which one. Some of them are absolute junk and not even worth the few Euros they cost.
You can of course send the board to me any time you like and I will diagnose (and fix) it for you if it's fixable.
Bryce.
This Plus arrived here last night. I've repaired the sound issue, Q106 had failed. That's the small KTC1815 transistor that drives the output. I haven't looked at the keyboard side of things yet because I have to go out now and it will take a bit longer because the AY replacement wasn't quite as perfect as stated above. There's at least two damaged pin holes and I'll need to go through them all. Job for tomorrow...
Bryce.
Finished the Plus this morning. Sound and keyboard are now doing what they should. Moving on to the classic 6128 now (also from Makinavaja). For reference, this one displays a blackish screen with flickering grey lines and has already had quite a bit of mods / repairs done to the board. I'll post the progress in this thread too as I don't think Makinavaja opened a seperate thread for it.
Bryce.
Edit: Oh dear! A bit of a thermal Christmas tree going on here. Any chance that this got connected to the wrong voltage or reversed polarity?
It's not suppose to look like that then? Is it showing most of the chips are fried?
Yup. I've done some diagnosis and almost everything that's connected to Data line D6 is fried. Looks more like a static discharge issue than an over-voltage. Lots of chip changing required I'm afraid. Luckily, the 40010 and the CPU (and possibly the 8255) have survived, but several logic chips, RAM and the CRTC weren't so lucky.
Bryce.
Oh my god u_u
I would say this: cpc comunity is SO LUCKY for having hardware masters like Brice, really.
I'm still looking for people doing the same for MSX systems...
Bryce, thank you very much!
Finally starting to get somewhere with the 6128. It now boots, but the keyboard is completely dead and I can't test the floppy circuitry yet, so I don't know whether that works either.
My first suspicion was that it had got a blast of static discharge, but I now think that it was a mistake I've seen before: High voltage on a data line (in this case D6). The CRTC, 74LS244, 74LS373 and both D6 RAMs had to be replaced to get this far. Last time I saw this type of failure was when someone used an unregulated soldering iron on a computer while it was still connected to a monitor.
Anyway, need to take a break now and get back to it later.
Bryce.
Edit: I don't just do CPC's, I do any retro computer.
Doh! My fault, I forgot to reconnect one of the pins on the 8255 that I had isolated. The keyboard and disk interface both work fine, the sound too.
Job finished, time for a beer :)
Bryce.
By the way... the fdc controller chip was fake or was good?
The FDC chip is a real one.
Bryce.
Edit: Aaaand parcel already on its way back to you....