Author Topic: Me and my Schneider CPC 464 again.  (Read 2364 times)

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Offline twox

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Me and my Schneider CPC 464 again.
« on: 17:17, 12 January 19 »
So, i've been dusting my shelf (once in years, mind you) and i found my old Schneider CPC464. I tried to repair it about 5 years ago, and i even made a topic on this forum (http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/my-schneider-cpc-464-don%27t-work/), you should check it for details.
I dropped it because back then the repair surpassed my possibilities, and i was simply scared to turn it on when it was "running" so i couldn't really check if the RAM is broken or some other part is visibly smoldering. Now i done that, and courtesy of phone i now have, i was able to make a short video where i show how it exactly looks (and sounds).
https://www.youtube.com/watch?v=BsCUgSpV4SY&As you can hear, when i turn on the switch, a sound reminiscent of popcorn popping is clearly heard. As you may have know, the switch itself doesnt mechanically make that sound, so it is from inside of the computer. And as you can see, i checked all the parts for unusual heat and none of them were hot (do i need to keep it running for longer before checking?)
Nothing have changed it the almost 5 years it have dusted on my shelf. Before i turned it on today i rudimentarily cleaned it with pressurized butane.A short recap of remedies i tried 5 years ago -
  • Cleaning with alcohol
  • I gave it off to someone who patched the power supply (or so i thought)
  • Resettling Z80
  • Resettling of Gate Array
  • Replacement of Gate Array
Now that i have much more possibilities in both expenses for new parts and in department of making better quality photos and videos for you guys to analyze, i think now it is the time to try fixing again. And in anticipation i already found a replacement Z80 that i can buy, but thats only gonna happen if you guys rule out that it is absolutely neccesary to at least try replacing it.I think i will try to make a complete batch of mainboard in methanol, because last time i only gently brushed it.Cheers and thanks in advance

Online Bryce

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Re: Me and my Schneider CPC 464 again.
« Reply #1 on: 17:39, 12 January 19 »
Two things:


1 - The popping is from the monitor and is a sign that it will give up working in the near future. So when the CPC works again you'll need to get some other solution for a power supply and screen (SCART cable or whatever).

2 - The Z80 is fine, otherwise that square wouldn't have appeared on the screen. Most likely some RAM has failed and this will need to be replaced.

Bryce.

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #2 on: 18:17, 12 January 19 »
I saw something glimmering and slimey near the power supply on the underside, i unscrewed the board and it turns out the guy who was "fixing" it used a exceptionally sticky piece of tape to isolate the patch. Ofcourse the slimey wet side was facing the exposed patch, and most propably it was sizzling. I have taken the piece away and put it the other way around, so it is still isolated but the glue isnt contacting power supply. I cleaned the power supply with pressurized butane. The frequency of sizzling lowered significantly (back then it was everytime, now ~1/6 of time).I also left it running for a longer time (about 8 minutes) and none of the chips were exceptionally hot - albeit the sound chip was a little bit hotter than others. They all were still no hotter than 40C.I also pinpointed the sizzling sound to the tape assembly. I put my ear dangerously close to both the mainboard and to the electronics that are under the tape player, and the sizzling is definitely from the latter. I also noticed that about 2/3 times the electronics under the tape (please tell me how they are called  ??? ) sizzle, something other than a rectangle appears, like a grainy *something*.I dont even know what are the purposes od this tape electronics thingy besides reading tapes and providing the switch, and IF there are. Please end my unawareness. Also, are there contraindications to just unscrewing this tape assembly and dumping it in alcohol to clean it? BTW, here are some (better than last time) photos of the patched power supply
https://imgur.com/a/veiHwAEThanks

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #3 on: 18:35, 12 January 19 »
I also recorded a video that shows those weird unusual images.The image shown on screen seems to always correspond to sounds of the tape electronics thingy. When it emits those cracking sounds, the image on screen twitches and moves.Dont mind the thump at 1:02  :-X
https://www.youtube.com/watch?v=5yxCEEcbkcc&

Online Bryce

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Re: Me and my Schneider CPC 464 again.
« Reply #4 on: 19:22, 12 January 19 »
You can't be "dangerously close" to a PCB that only has a 5V 2A supply. At 10W you could lick the board and still wouldn't be in danger.

The sounds you are hearing are more likely to be the normal processing sounds, and all that switching on and off isn't going to change anything. You need to send the PCB to someone who can fix it for you.


Bryce.

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #5 on: 20:25, 12 January 19 »
I meant dangerously close for the PCB ;p Last time i checked my ears were conductors.Unfortunately i dont know anyone that could fix the PCB (shit i dont know many people in general). And once i did this and the guy sent me back a supposedly fixed PCB that was "working" exactly the same way that it was when i sent it.
Can faulty RAM be detected with a multimeter? Because none of them feels hot. I dont feel like swapping 8 of them with a primitive 45 years old solderer.

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Re: Me and my Schneider CPC 464 again.
« Reply #6 on: 20:30, 12 January 19 »
RAM doesn't always get hot when it has failed, but you also won't be able to test it with a multimeter. You could send the PCB to me (in Germany) if you like. I will definitely not send it back broken. Not sure what the postage back and forth will cost, but if you have no local repair options, I'm probably the closest.


Bryce.

P.s. Even "conductive ears" aren't conductive enough to cause a danger to the PCB :D

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #7 on: 21:48, 12 January 19 »
Hmm. From Poland to Germany i can post this as a registered priority mail for exactly 28PLN (~7$), in a plastic bag wrapped in bubble wrap. Expected delivery time 3 days. From Germany to Poland, i think something like this will be viableI can send you money for postage and work directly in the mail. Please respond with how much you would want for it, and how long would it take. Cheers

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Re: Me and my Schneider CPC 464 again.
« Reply #8 on: 14:10, 13 January 19 »
Pm on its way to you....

Bryce.

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Re: Me and my Schneider CPC 464 again.
« Reply #9 on: 22:20, 23 January 19 »
So twox's 464 arrived last night and I had time to look at it tonight. As there is often talk about RAM failures and temperatures (ie: "none of the RAM ICs are hot, so they must be ok" etc), I thought I'd share some data with the Forum here.

Firstly the good news for twox: The issue is two failed RAM's, I'll fix it by the weekend and get it back to you as soon as possible.
Now to temperatures. I used the excellent RAM test from @gerald to establish which RAM's had failed (it was D1 and D3). On the cost down 464 the order of RAMs is different to the standard 464's and 6128's, they are not in order, which can be quite confusing. From top to bottom the order is D3, D2, D1, D0, D4, D5, D6, D7. Looking at the thermal picture, the RAM's are obviously hotter than the other RAM's, however, the difference is tiny and not noticable by touching. Althought the top RAM and third RAM light up like a christmas tree in the thermal picture, the actual difference was only 1.2°C

This is not to say that failed RAM's don't get really hot, they do, they can burn your fingers, but it's not always the case. RAM's can fail and the difference is not or barely noticable.

Time to get the soldering iron fired up.

Bryce.


 
« Last Edit: 15:23, 24 January 19 by Bryce »

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #10 on: 17:01, 24 January 19 »
Hmm.. Is it completely unreasonable to think that the patched power supply caused the damage of those RAM chips? If so, replacement of those would be just sprinkling shit with sand (an old Polish saying).Cheers

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Re: Me and my Schneider CPC 464 again.
« Reply #11 on: 09:35, 25 January 19 »
No, the patch couldn't have caused this, however, the patch is a bit messy, so I will fix that up too while I have the iron on.

Bryce.

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Re: Me and my Schneider CPC 464 again.
« Reply #12 on: 16:50, 26 January 19 »
So. Just finished the repair and your computer is back up and running. I also cleaned up the old power socket repair as much as it could be.

Bryce.


 

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #13 on: 17:24, 26 January 19 »
 :o My father will have a hell of a suprise! Lets hope that he wont spill Commie-Coca cola on it this time! Now lets hope that the tape deck and keyboard are functional..Cheers

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Re: Me and my Schneider CPC 464 again.
« Reply #14 on: 17:30, 26 January 19 »
I tested the AY for keyboard input and sound, so if there are keyboard issues it will be from the physical keyboard, not the electronics and that usually just means it needs to be cleaned (at least on the 464's). The tapedeck should also be fine is the belts are good and it has been cleaned.


Bryce.

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #15 on: 17:41, 26 January 19 »
So.. I dont know if am just delusional, but i remember that 5 years ago i tried the tape deck with some generic music tape and it played the music fine (as fine as the poor speaker could). Judging by the fact that CPCs make this sound when reading tapes, why wouldn't they play music tapes?

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Re: Me and my Schneider CPC 464 again.
« Reply #16 on: 18:11, 26 January 19 »
Because the CPC has some filters and comparators that are optimised for converting frequencies into digital bits. You would hear the music, but it would sound terrible.

Bryce.
 

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #17 on: 18:22, 26 January 19 »
IMHO it was still better than motivational song for polish Euro 2012 team.

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #18 on: 14:56, 05 February 19 »
So.. My 8-bit machine powered by Z80 arrived today and this happened:
https://www.youtube.com/watch?v=VtuJ8u-PKbs
Spoiler: show

But seriously, there are still some faults.
  • Spoiler: show
    Keyboard keys are mushy like squishing stress balls (but atleast they all work)
  • Spoiler: show
    Sometimes right after startup computer emits a high pitched sound
  • Spoiler: show
    Tape reader didn't read my 'car audio adaptor' tape, but it was rotating so i suspect just dirt or faulty audio adaptor
Cheers
« Last Edit: 15:06, 05 February 19 by twox »

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Re: Me and my Schneider CPC 464 again.
« Reply #19 on: 15:13, 05 February 19 »
 :D You didn't have me fooled. I tested the shit out of it before sending it back!

Regarding the other issues:
Keys: That's how they always were, you're just to used to using modern keyboards.
High pitched sound: That's coming from the monitor and is a sign that the monitor may not live all that long, the HV coilis getting old.
Tape: Clean the heads.

Bryce.

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #20 on: 15:27, 05 February 19 »
We all know that your heart skipped a beat  :laugh: Anyways, i fiddled around with the sound potentiometer and when i did it it also produced those pitches. Shit, i hope it is that the speaker is faulty not the monitor, because i heard those are nasty to repair and can kill you (and i've never ever repaired them).. I've had enought of CRT's producing those aggresive electronic cracks when i used them all the way to 2016. Fortunately i lived all the way trought (my power supply was another story..)I think that now i need to educate myself about tape head cleaning.Cheers

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #21 on: 16:05, 05 February 19 »
BTW.. Is overscan 100% physically safe for those GT65? I plan to play some overscan games and i dont want to make a BBQ in my room.. Especially that my GT65 definitely isn't in mint condition. Cheers

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Re: Me and my Schneider CPC 464 again.
« Reply #22 on: 16:17, 05 February 19 »
Overscan doesn't have any physical effect on the monitor, all it does is put more data onto the screen (ie: reduce the border). The monitor scans exactly the same as it normally would.

Bryce.

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #23 on: 16:30, 05 February 19 »
Weird.. I could place the cotton stick i used to clean the head back to its container and nobody would notice (Not that my family reuses cotton sticks...)No effect. Theres some rustling in the adaptor itself, i think it is broken. I will check it in my car, i was going to the garage anyways. And i will look for some of the "original" tapes when i am at it. Cheers

Offline twox

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Re: Me and my Schneider CPC 464 again.
« Reply #24 on: 17:55, 05 February 19 »
So it turns out that the player in my car is broken. i found some unlabeled tapes, i will try saving on them and then running. CheersEdit: as it turns out saving/reading from a regular tape worked fine. I will continue to tinker with the adaptor.
« Last Edit: 18:02, 05 February 19 by twox »