Author Topic: CPC6128 power supplies - must both 12v and 5v be connected?  (Read 4111 times)

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Offline ibisum

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Hi all,


I finally got my long-coveted CPC6128 hardware, sans monitor/power supply, and have been trying to debug its setup this evening .. for this bit of retro-tastic adventure I purchased one of the SCART cables from retrocomputershack.com, which were recommended to me by other Amstrad aficionado's, and I have an HxC (Rev F) drive as well, for when I eventually get the machine up and running.


To give it a quick test today, I wired it up with a 5V/4A power supply, proper polarity, just to see if I could get something on the screen - alas, it is not to be.  The seller provided me with a video of the system working before he shipped it, so its got to be my problem I suppose. 


The question I have is, do I have to have both 5v and 12v wired up in order to get it to boot properly - or is it such that I could operate it without the disc drive being powered up?  I don't have the barrel adapter required to get a 12v supply wired up to it yet, so I was kind of hoping I would be able to do this with just the 5V adapter .. anyone wanna clue me in on my stupidity here?


I'm not getting very good results - the TV I am using (SABA) is decent quality and works with my other retro systems just fine (Oric Atmos and C64), so I know its not the monitor at least .. so perhaps I've just gotten too ahead of myself and need to go to the hardware shop to get the required parts to make the 12v lead?


Or .. *shudder* .. have I screwed things up by trying to power up the CPC6128 with just 5V alone?  Also, the fact that its a 4A adapter - does this mean I've potentially screwed my system, which everything I've read on the Internet says should "just work" with a "5V/2A" adapter .. I sure hope that I haven't fried anything.  Or, if I have, I'll be starting a new thread to discuss my debugging and replacement of fried parts, alas ..

Offline Duke

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5V alone, is all the CPC needs to power up. 12V is only for the disc drive and if using Gotek, you don't need 12V either.

Offline tjohnson

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Hmm if the polarity is fine, the connector the right size and power supply is kicking out 4a at 5v that should be more than sufficient to boot to basic.   Does your led come on when using the power switch?

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Offline tjohnson

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If you get an led, using delete key try deleting something got should get a beeping sound out the speaker too. 

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Offline chinnyhill10

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Or .. *shudder* .. have I screwed things up by trying to power up the CPC6128 with just 5V alone?  Also, the fact that its a 4A adapter - does this mean I've potentially screwed my system, which everything I've read on the Internet says should "just work" with a "5V/2A" adapter .. I sure hope that I haven't fried anything.  Or, if I have, I'll be starting a new thread to discuss my debugging and replacement of fried parts, alas ..


I run all my CPC's on 4 Amp supplies. The supply can go up to 4 amps but will only supply what the CPC needs. So you are fine.


I did a quick and messy video on my phone at Christmas when a known good CPC came out of storage and it wouldn't turn on:



http://www.youtube.com/watch?v=KlE7w0qRzsY


Basically your first port of call if you have no light on the LED is the power switch. No need to replace it, it just needs contact cleaner and it will be as good as new after its been switched a few times.
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Offline ibisum

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Thanks for the helpful replies guys - and sorry for the newbie question, I've since learned that this is a FAQ in this forum and I appreciate your patience.


So the symptoms are: the machine starts up, it clearly gets power - the LED on the floppy and on the main case unit both come on, and there is a flicker on the screen when I turn the switch on - however, pressing DEL does not result in any sound, nor do I get anything legible on the screen at all.  There are just three flickery lines, each a different colour (red/blue/green) which don't seem to go away when I turn the CPC6128 off and on.. so I'm not sure if these are an artefact of the CPC612's condition, or just a side-effect of my ancient TV doing 'something' with the SCART signal (and just to confirm this TV works great with other micro's such as my Atmos) .. I don't have a floppy disc yet (was planning on going straight to HxC) so I can't do a floppy "CAT" test (as is recommended elsewhere) to see if there is any response on the drive, alas.


So I'm a bit stumped - it would appear that I have to go through the "more intensive debug" dance: GA, RAM, Z80 cpu, etc.  Drats, I was kind of hoping to avoid opening the case so soon. ;)


Anyway I'm going to wire up a proper cable to give me 12v just so I can see if the floppy works with a "CAT" command, and .. if that produces nothing, I'll pop the case and start going through the debug dance ..
« Last Edit: 09:23, 08 May 18 by ibisum »

Offline tjohnson

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Did you buy it working on eBay or with paypal? If so talk to the seller about a refund these are robust machines so seems unlikely it broke in the post.

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Offline CraigsBar

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Thanks for the helpful replies guys - and sorry for the newbie question, I've since learned that this is a FAQ in this forum and I appreciate your patience.


So the symptoms are: the machine starts up, it clearly gets power - the LED on the floppy and on the main case unit both come on, and there is a flicker on the screen when I turn the switch on - however, pressing DEL does not result in any sound, nor do I get anything legible on the screen at all.  There are just three flickery lines, each a different colour (red/blue/green) which don't seem to go away when I turn the CPC6128 off and on.. so I'm not sure if these are an artefact of the CPC612's condition, or just a side-effect of my ancient TV doing 'something' with the SCART signal (and just to confirm this TV works great with other micro's such as my Atmos) .. I don't have a floppy disc yet (was planning on going straight to HxC) so I can't do a floppy "CAT" test (as is recommended elsewhere) to see if there is any response on the drive, alas.


So I'm a bit stumped - it would appear that I have to go through the "more intensive debug" dance: GA, RAM, Z80 cpu, etc.  Drats, I was kind of hoping to avoid opening the case so soon. ;)


Anyway I'm going to wire up a proper cable to give me 12v just so I can see if the floppy works with a "CAT" command, and .. if that produces nothing, I'll pop the case and start going through the debug dance ..
Can you provide a photo of the screen please


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Offline ibisum

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@tjohnson: by Paypal, and I've been in touch with the seller, he's a good bloke.  I trust he didn't sell me dodgy gear, so I'm quite willing to work through this issue if I can .. part of what I got it for is to get a few burnt fingers here and there .. ;)   Its the retro-lovin' lifestyle.

@CraigsBar: Sure, here you go - sorry for the potato quality image, but I think you can see the effect nevertheless - it should be noted that these lines appear whether there is power attached to the CPC6128 or not, which makes me a little suspicious of the SCART cable, actually .. I do have another one that I could try, although it is a different configuration than this one from RetroComputerShack ..
« Last Edit: 12:39, 08 May 18 by ibisum »

Offline tjohnson

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Where do you live there might be a member able to help locally
@tjohnson: by Paypal, and I've been in touch with the seller, he's a good bloke.  I trust he didn't sell me dodgy gear, so I'm quite willing to work through this issue if I can .. part of what I got it for is to get a few burnt fingers here and there .. ;)  Its the retro-lovin' lifestyle.

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Offline ibisum

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@tjohnson I'm in Vienna, Austria - I do have plans to have a Retro- meet up at the local hackerspace (Metalab) in the next week or so and I'm sure there are other Amstrad users out there, but I'd honestly prefer to go to that meeting with a working Amstrad rather than spend time debugging it ..  ;D  .. so thats why I'm busy bugging you experts about it, lol ..

Offline ibisum

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.. okay just as a followup, I've tried the second SCART cable (with a 9v battery lead to provide power to SCART) and I get exactly the same result .. interesting thing is that the lines show up with the second cable, even unattached to the Amstrad, so I guess this is a red herring in that its just 'normal' display for a non-driven SCART cable (i.e. when it doesn't get a signal from the computer) .. and just to be sure, I hooked up my Atmos to verify the monitor is still working and there is no issue there, its a perfectly stable picture.


So I guess the CPC is just plain dead, and I've gotta open it up, give it a clean, check for bad RAM, bad Z80, etc.


One thing I just noticed - I double-checked the rating of the power supply I'm using, and even though its says it provides 4A, my meter shows only 2A been provided (and yes, its for sure 5V) - so maybe one last thing I can do before I start the long road of debugging components, is find another power supply that I know for sure provides >2.4A, as I've seen a lot of comments that the CPC is very finicky about this.   Had a similar problem with my Atmos when I powered it up, had to go through a few power supplies .. I've got a PC power supply that provides both 5V and 12V in the one connector, so I'll go get parts this afternoon to make a cable and see if that will give me a better result. 


Thanks again folks!

Offline Bryce

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Hi ibisum,
     first, to clear things up about power supplies, devices and amps: The amps stated on a PSU is what it CAN supply. The amps rating written on the CPC is what it needs AT MOST. Devices only take what they need: Converting amps to beer: My local pub CAN supply 1000's of litres of beer (PSU rating), my record consumption lies somewhere around 12 Litres (CPC rating), however during a standard evening in the pub I only drink 3 Litres (what you're reading from the meter).
So the 4A on your PSU is correct, as is the 2.4A on the CPC, but... 2A for an idling CPC seems a lot, looks like something has failed in there. You could try reseating the socketed ICs, but I suspect there is something more serious going on.

Bryce.

Offline ibisum

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@Bryce  Thanks for the clarification - its clear now, re: amps.


But, I did not measure the amps while the Amstrad was plugged in - just, with my multimeter.  So its not the Amstrad providing such a load, but the meter - which I guess, is not an accurate way of measuring amperage on the wire?


Anyway, I'm off to the shops to get a few more power supply bits, so maybe .. hopefully .. I'll have some good news in the next few hours.

Offline Bryce

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You can't measure amps without a load, because the load decides how many amps will flow. That still makes the 2A reading quite suspect, because (assuming you were using the meter correctly) inside your meter there's more or less a copper bar (known as a shunt) shorting the two probes. In reality the shunt is a known resistance of very low value. The meter calculates the amps, by measuring the voltage before and after the shunt and then uses ohms law to calulate what the current is. (Vin - Vout / Shunt resistance = Amps).

However, if no load was present, then you are essentially shorting the power supply which should cause the PSU to try to supply as much current as possible. In an expensive PSU, this would probably cause a reading of maybe 10A, but the voltage would drop to about 2V or less. A cheap PSU would just go bang and some smoke would come out.

Bryce.


Offline ibisum

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Yes, thats what I understood to be the case .. its not a super expensive supply and it works fine on other gear.  Regardless, I'm off to get a new proven supply for this machine.  I hope I can get some results today.

Offline chinnyhill10

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If you get an led, using delete key try deleting something got should get a beeping sound out the speaker too. 

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Try this. Press Del or CLR with the volume turned up on the CPC. If you get a beep that eliminates a lot of issues.
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Offline Bryce

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- however, pressing DEL does not result in any sound

Bryce.

Offline dragon

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Thats not definitive anyway, if was me,  i try put a headphone  in 3,5mm jack with the del key test. In the other hand yo can write a blind command, a | tape + ctrl + intro + a key example to view if the tape relay try to do something to avoid the del key. or press varius keys until he reach the top and generates the del sound.
« Last Edit: 21:33, 08 May 18 by dragon »

Offline tjohnson

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Thats not definitive anyway, if was me,  i try put a headphone  in 3,5mm jack with the del key test. In the other hand yo can write a blind command, a | tape + ctrl + intro + a key example to view if the tape relay try to do something to avoid the del key. or press varius keys until he reach the top and generates the del sound.
Turning the machine on and pressing del repeatably will generate a beeping sound but yes it is possible the speaker could be faulty

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Offline tjohnson

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Yes, thats what I understood to be the case .. its not a super expensive supply and it works fine on other gear.  Regardless, I'm off to get a new proven supply for this machine.  I hope I can get some results today.



what further progress?

Offline chinnyhill10

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what further progress?


Probably like me and my French 464. Good advice from Bryce and other users but simply haven't had the time to take it apart yet. And I also have an Amiga 600 in bits awaiting parts. We're like your Dads mates who when you go to their house they own 10 old cars, most of which don't work as they need parts or fixing!  :laugh:
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Offline ibisum

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Sorry guys - just a little bit behind the ball with this project at the moment .. my attempts to use my local power supplies haven't been fruitful, so the last thing I will do is try a PC power supply - but for that I have to make a trip to the hardware store for cable accessories .. some time today hopefully, so I can pick it up again this weekend and determine just how terrible (or not) things are with my CPC6128 .. I really appreciate the help so I'l be back with news shortly ..

Offline ibisum

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Okay .. an update .. I bought a fresh 5V/3A adapter, and I've switched out the TV for another, different one.  I also have a SCART/HDMI adapter now, and tried that too.  No matter what: CPC6128 does not boot.


 :(


Well, I now prepare my workbench for an evening of opening the case, re-seating what can be re-seated, and going through whatever test procedures I can find - I think I saw a test manual for the CPC6128 in this wiki somewhere, so I'll be studying that this evening.  If anyone else has any other tips for dead-CPC recovery, I'm all ears ..


Online robcfg

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Here you'll find the service manual.


Good luck!