Author Topic: Me and my Schneider CPC 464 again.  (Read 183 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
Sorry for my bad english.

Offline 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
Sorry for my bad english.

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&
Sorry for my bad english.

Offline 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.
Sorry for my bad english.

Offline Bryce

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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
Sorry for my bad english.

Offline Bryce

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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.