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CPC6128 Power Connector Polarity

Started by trellis, 15:34, 15 May 09

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trellis

I have just taken delivery of a CPC6128 (courtesy of eBay) but I have no monitor to go with it, so no means of powering it. I happen to have a 6-pin DIN to SCART cable already, which I can simply re-wire at the SCART end to use with a TV, so power is the only problem.

I was delighted to see that both 12v and 5v power connectors are the bog-standard 2.1mm "Barrel" type DC power plugs, but there is no indication on the casing or in the manual of the correct polarity for each plug.

A bit of experimenting with a multimeter *suggests* that the -ve is the PIN on the 12v connector, but the pin of the 5v connector is +ve, so they're reversed ???  ??? :o

Can anyone advise?

Thanks.

mr_lou

I can't help you on polarity, but I want to tell you that you must be careful. Make sure you use a stabilized powersupply. Otherwise you can easily toast your CPC, if it gets too much voltage.

trellis

Quote from: mr_lou on 06:17, 16 May 09
I can't help you on polarity, but I want to tell you that you must be careful. Make sure you use a stabilized powersupply. Otherwise you can easily toast your CPC, if it gets too much voltage.
Acknowledged - thanks.
My plan is to use my Spectrum +3 Power-supply, which handily provides the right voltages (regulated) and plenty of amps. I'm making up an adaptor cable so I don't have to butcher the +3 PSU. Just need confirmation on the plug polarities to avoid frying the CPC  :D

arnoldemu

Quote from: trellis on 15:34, 15 May 09
I have just taken delivery of a CPC6128 (courtesy of eBay) but I have no monitor to go with it, so no means of powering it. I happen to have a 6-pin DIN to SCART cable already, which I can simply re-wire at the SCART end to use with a TV, so power is the only problem.

I was delighted to see that both 12v and 5v power connectors are the bog-standard 2.1mm "Barrel" type DC power plugs, but there is no indication on the casing or in the manual of the correct polarity for each plug.

A bit of experimenting with a multimeter *suggests* that the -ve is the PIN on the 12v connector, but the pin of the 5v connector is +ve, so they're reversed ??? ??? :o

Can anyone advise?

Thanks.
www.cpctech.org.uk

look for pc power supply in docs
My games. My Games
My website with coding examples: Unofficial Amstrad WWW Resource

trellis

Quote from: arnoldemu on 13:50, 20 May 09
www.cpctech.org.uk

look for pc power supply in docs
That leads to: http://www.kjthacker.f2s.com/docs/mods/power.html
which still only makes very brief mention of the polarity for one of the connectors (the very last line on the page!), and it is far from clear which connector it's talking about. So I'm still none the wiser, but thanks for the link.

Grim

#5

EDIT: POTENTIALY DANGEROUS.

I've attached a picture showing the polarity of the 5v power line that plug in the CPC. The ground is on the outside (for safety reasons) and the 5v on the inside.

The 12v power line for the 3" drive use the same scheme but with 12v instead of 5v.

trellis

Hmmm.  ???
Are you absolutely certain that the 12v connector is not reverse wired?

I'm not disputing what you say, it's just that it goes against what my continuity tests suggested, and I don't want to blow the thing up by wiring the PSU up the wrong way round  :o

I just checked again with a multimeter, and the OUTSIDE of the 5v connector, the PIN of the 12v connector and the GND pin of the RGB socket are all connected together, suggesting that these are all GROUND.

If this is true, then the 12v plug must be wired with the OUTSIDE as +12v and the PIN as GROUND.

I don't suppose anyone would be willing to check their PSU output with a multimeter and confirm this would they?

the KING

Come on guys..... there must be someone out there with a 6128/664 and a voltmeter!
It's killing me that we can't get a clear answer for such a basic question....  :o
Tom

ukmarkh

#8

trellis

Well, I would vehemently disagree with some of the stuff in ukmarkh's post (where is that from, incidentally?).

Just because it's a big, heavy power supply /does not/ mean it is unregulated. Many big, bulky linear power supplies have regulated outputs.

The advice to 'just plug it in and try it' is also very misguided, as this could result in destruction of the device, the power supply or both. If the power supply is not fused, it could even result in the power supply or cable overheating and causing a fire.

Also if you use a power supply with a higher output voltage than that the device is designed for, the regulation circuit in the device will have to dissipate more power as heat, and could overheat and either damage itself or cause a fire.

Very bad advice on several counts.

ukmarkh

#10
Quote from: trellis on 13:59, 23 May 09
Well, I would vehemently disagree with some of the stuff in ukmarkh's post (where is that from, incidentally?).

Just because it's a big, heavy power supply /does not/ mean it is unregulated. Many big, bulky linear power supplies have regulated outputs.

The advice to 'just plug it in and try it' is also very misguided, as this could result in destruction of the device, the power supply or both. If the power supply is not fused, it could even result in the power supply or cable overheating and causing a fire.

Also if you use a power supply with a higher output voltage than that the device is designed for, the regulation circuit in the device will have to dissipate more power as heat, and could overheat and either damage itself or cause a fire.

Very bad advice on several counts.

Always worked for me... especially with consumer branded devices, but yes! You do have to be careful. Although I've only ever used a power supply with the correct output/voltage that is needed for the device. I power, and modded my Symbiface 2 to run off a LITEON AC Adapter (Input: 100-240V 1.2A / Output:12v 3.33A) and it works fine, as do several other items I run from the Amstrad. So I must be doing something right! 

trellis

Quote from: ukmarkh on 14:04, 23 May 09
Always worked for me... especially with consumer branded devices, but yes! You do have to be careful. Although I've only ever used a power supply with the correct output/voltage.
Indeed! And "being careful" in this instance means "wiring it up correctly in the first place"  :D

trellis

Quote from: ukmarkh on 14:04, 23 May 09
I power, and modded my Symbiface 2 to run off a LITEON AC Adapter 12v 3.33A and it works fine, as do several other items I run from the Amstrad. So I must be doing something right!
Well, this is entirely right! You've wired a correctly-rated power supply up correctly - this is exactly what I am trying to do!

What your previous post said was that you could just pick up any old power supply and try powering some random device with it, without checking output voltage or polarity. That's what I was disagreeing with.

ukmarkh

#13
Quote from: trellis on 14:20, 23 May 09
Well, this is entirely right! You've wired a correctly-rated power supply up correctly - this is exactly what I am trying to do!

What your previous post said was that you could just pick up any old power supply and try powering some random device with it, without checking output voltage or polarity. That's what I was disagreeing with.

I also stated you could open up the power adapter and check for yourself... There is trial and error in everything... the stuff I've done works so far, and I do take saftey precautions. A pattern develops once you've seen the first thousand different Adapters, and you get a feel for which ones can power a certain device, and it's a skill I rely on - especially if all the writing has been rubbed off. It's just me though, and I wouldn't / shouldn't recommend it to anyone else, and people with no experience dont' even go there.

trellis

Quote from: ukmarkh on 14:26, 23 May 09
I also stated you could open up the power adapter and check for yourself... There is trial and error in everything... the stuff I've done works so far, and I do take saftey precautions.
Fair enough, we won't have a blazing row about it  ;)
In this instance, I think I'd rather get it right first time, rather than use trial-and-error  ;D

ukmarkh

#15
Quote from: trellis on 14:32, 23 May 09
Fair enough, we won't have a blazing row about it  ;)
In this instance, I think I'd rather get it right first time, rather than use trial-and-error  ;D

You realise everything ever invented from a technology point of view was initially based on trial and error... that's all i'm trying to say. You have a skillish way with words... lol

Let's know how you get on.

trellis

Quote from: ukmarkh on 14:36, 23 May 09
You realise everything ever invented from a technology point of view was initially based on trial and error... that's all i'm trying to say. You have a skillish way with words... lol

Let's know how you get on.
;)
Yep, I will report back how I get on.


trellis

OK, I've added a Wiki page on this.
Hope it's useful to others.

trellis

Quote from: trellis on 17:32, 24 May 09
OK, I've added a Wiki page on this.
Hope it's useful to others.
And just to prove it works and I am not fibbing, here is a picture of my 6128 running from a Sinclair +3 Power Supply, using a home-made SCART cable for RGB output (actually it's a Tesco Value SCART lead that I chopped one end off and wired into a 6-pin DIN).

http://www.zen13412.zen.co.uk/100_0456.JPG

:D

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