GX4000 Power Advice

[ashleary]

I bought an 'untested' GX4000 from eBay (at £20 I thought it was a steal) even though I kinda expected it not to work. So I wasn't surprised (although Ill informed) when 'with all wires and manual's' meant all wires except for the original power lead, but I'll include a multi power adapter thingy and sneakily leave it in just tucked in the back of the photo.
Anyway, I've plugged it in, and whilst a power light comes on and (when using the RF) there is a noticeable change in the static on screen, no game actually starts. I've tried switching to 5v in the 5v port - nothing - but only 9v in the 11v port. I know it sounds daft (but I'm not totally electronically savvy) but would 9v do anything in an 11v port? A couple of posts on a forum have said they got an unstable crashing system with 9v? That being said, would 12v fry it?
I've tried using the RF and the scart adapter, both with the same results.
Can anyone offer any advice?
Cheers.

[chinnyhill10]

Sounds like exactly the same way every GX4000 I've had failed. LED comes on, it will display either a black or grey on the screen, but that is it.


You can try cleaning the cart edge connector and the cart slot but I doubt it will make much difference.


You might get lucky and it works with a proper supply but I doubt it. I'd never touch an 'untested' GX4000. Only ones that are proven working. "untested' is Ebay code for "I turned it on and it didn't work".

[ashleary]

"untested' is Ebay code for "I turned it on and it didn't work".

Its funny because it's true


Will try cleaning it, and then bang it back on eBay a the price I paid for it with a true description in the hope that someone can buy it and fix it!

[keith56]

please see my comments in the post below about the gx4000 and it's power/video oddetites

http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/gx4000-psu/msg142291/#msg142291

I use a 10v center positive adapter which works fine.

The best thing to do is listen for music on the scart connectior

Burning rubber plays music automatically - and that will mean even if you're having scart video problems you should hear something!

[Bryce]

Hi and welcome ashleary,
       first here's some electronics info: The GX4000 uses a 7805 regulator to create the 5V rail. These need at least 8V to work properly. Your PSU may say 9V, but how much is it exactly? By the time the current gets to the regulator it will have dropped slightly due to resistance in the wire / socket etc. How much current can the PSU supply? If it's only barely enough for the GX4000, then the voltage may be dropping further becasue it can't supply the load. As you get closer to 8V the regulator will start dropping out.
So to answer your question: Yes, the GX4000 may work with some 9V supplies, but it's by no means guaranteed.

Bryce.

[1024MAK]

Be careful with DC Mains Adapters / Plug top power supply units (PSU). Alas some people just plug in any old PSU and try. That may be what a previous owner did.

First, there is no standard power connector, so whenever you are not using the manufacturers original PSU, always double check the output connector is the correct polarity. If you have a multimeter, test it as well. If the polarity is wrong and you try to power it up, most equipment will be damaged.

Second, with DC PSUs there are various types. I won't list all the types, but just be aware of this. The most important thing to know, is that the two main categories are "smoothed but unregulated" and "regulated". If it does not say "regulated", it is very likely a smoothed but unregulated" type. The output voltage of the unregulated type depends on how much current the load is drawing from the PSU. With the PSU not connected to a load, the output voltage may be well above the value on the label. With a regulated type, the voltage should stay close to the rated voltage (unless you exceed the rated current).

Third, as Bryce says, the voltage and the currrent ratings are important. So called universal PSUs with a switch to select the output voltage often cannot supply the same output current on all voltage settings.

So best post a photo of the PSU you have. And post here all the rating label information.

Mark

[keith56]

Be careful with DC Mains Adapters / Plug top power supply units (PSU). Alas some people just plug in any old PSU and try. That may be what a previous owner did.

Couldn't agree more! Many people seem to think all adapters are centre positive, but it's not always true!

Almost all Japanese 1980/90's consoles are 10V centre negative... and uk Nes/Snes are AC not DC adapters

[ashleary]

Hi there,


Here is the Amazon link to the PSU that was in the box
https://www.amazon.co.uk/AKORD-Voltage-Transformer-Adapter-2000ma/dp/B00WOIV8NE/ref=sr_1_1?ie=UTF8&qid=1489490450&sr=8-1&keywords=multi+volt+adapter+dc


Any thoughts - advice?


I suspect, as 1024MAK has said, "this may be what the previous owner did".


In my belly, I'm thinking that this thing is shot, but I'm ever hopeful that one of you folks's advice will get me up and running.


On that same vein, I'm amazed (and pleased) at the response I've received in such a short space of time on a topic and series of systems that old (yet awesome and give me fond memories)


Cheers.

[1024MAK]

Going on the answers and comments, it looks like that PSU is suitable.

Mark

[ashleary]

What voltage would you advise I set it to?

[chinnyhill10]

With those multi-tip adaptors you have to be very very careful not to put it in the wrong port on the GX. 5v in the 11v port doesn't matter. 11v in the 5v port will kill the ASIC. I know, I've done it.

[Bryce]

@1024MAK: The "regulated or just rectified" question isn't really important on a GX4000 as it has its own regulator inside (only on the 11V input!). It's extremely important on all the other CPCs though because they have zero regulation or protection inside.

@ashleary: I would set the PSU to 12V and use it on the 11V input. This will probably offer the most stable configuration. Put some tape over the 5V socket to stop yourself from accidentally using it.

Bryce.

[keith56]

Just put some tape over mine too - I hadn't heard about this asic frying horror!
If you have a test meter, I'd test the polarity of the adapter before you plug it in, better safe than sorry!

[ashleary]

With those multi-tip adaptors you have to be very very careful not to put it in the wrong port on the GX. 5v in the 11v port doesn't matter. 11v in the 5v port will kill the ASIC. I know, I've done it.

If the ASIC has been fried already will I know (the LED currently comes on - is this an indicator that it's currently ok?)


The 11v is the one closest to the SCART socket yeah?

[1024MAK]

The power on LED only indicates that there is some power on the 5V internal power network. If you are using the 11V DC power connection, it is likely that the internal 7805 voltage regulator chip is working.

Mark

[chinnyhill10]

If the ASIC has been fried already will I know (the LED currently comes on - is this an indicator that it's currently ok?)

No, every fried GX4000 I've ever seen, the light still comes on.

[ashleary]

No, every fried GX4000 I've ever seen, the light still comes on.

Might take it to bits when I get in from work. Are fried bits easy to spot or will i need a multi-meter (aka learn how to use a multi-meter...)

[1024MAK]

Might take it to bits when I get in from work. Are fried bits easy to spot or will i need a multi-meter (aka learn how to use a multi-meter...)

Unless the board was severely over cooked there is unlikely to be much (if any) visible damage. A digital multimeter can check the voltages on the power supply network, and check for short circuits. But is not very useful on the high speed digital signal lines. A digital multimeter updates about 3 to 4 times a second. Not a lot of use on signal lines running with signal changes measured in Micro seconds.


To see what is happening on such signal lines means you need a suitable oscilloscope and maybe a logic analyser. But a suitable 'scope will cost many times the value of the GX4000.

Mark

[Bryce]

If you are at the "need to learn how a multimeter works" level, then there's nothing inside that you will be do to fix it. You'll need to send the PCB to someone who can test it properly.

Bryce.

[ashleary]

Unless the board was severely over cooked there is unlikely to be much (if any) visible damage. A digital multimeter can check the voltages on the power supply network, and check for short circuits. But is not very useful on the high speed digital signal lines. A digital multimeter updates about 3 to 4 times a second. Not a lot of use on signal lines running with signal changes measured in Micro seconds.


To see what is happening on such signal lines means you need a suitable oscilloscope and maybe a logic analyser. But a suitable 'scope will cost many times the value of the GX4000.

Mark

If you are at the "need to learn how a multimeter works" level, then there's nothing inside that you will be do to fix it. You'll need to send the PCB to someone who can test it properly.

Bryce.

Taken on board.


Cheers folks

[gerald]

Most of the GX4000 I serviced suffered from dead RAM.
Some also had they 5V regulator(s) dead.

You can have alook there for where to look on the board for these parts: http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/%28please-read%29-gx4000-with-original-power-brick-and-c4cpc/

Note that the 5V regulator is always powered. The on/off switch is on the 5V rail so you can check it without powering the whole circuit.