Author Topic: CPC-464 blank screen at start up.  (Read 3999 times)

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Offline magentis

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CPC-464 blank screen at start up.
« on: 01:44, 24 February 15 »
So i got my cpc-464(its the long board type) out of storage and things are not good,i have a gt-65 monitor with it and i just get a dark green screen with a light green border on start up.
The cassette fast forwards and rewinds but wont play.
I tried entering blind commands but it does nothing.
I measured the output from the monitor and i got 5.23 volts steady.
I swapped the Z80 with the one from my +3 and it made no difference.
None of the chips appear to be getting warm.
I checked the RAM ic's with the multimeter and got 5.1 volts at all of them,is this the only voltage input that these chips need?
Im not to familiar with the innards of a cpc,so any ideas would be most gratefully appriciated.

Offline Bryce

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Re: CPC-464 blank screen at start up.
« Reply #1 on: 10:47, 24 February 15 »
Hi magentis,
     sorry to hear about your CPC woes. First off: Yes, the RAM ICs only need 5V. "Play" only works after you've done a Run" command and Pressed any key, so the tape functionality is correct. I assume you've checked whether it beeps when you hold down "DEL" ? Have you also cleaned the contacts on the monitor output connector and checked that the brightness etc on the monitor is up high enough?

What equipment do you have for testing?

Bryce.

Offline magentis

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Re: CPC-464 blank screen at start up.
« Reply #2 on: 21:02, 27 February 15 »
Hi Bryce,thanks for the reply.[/size]Should it beep when del is held down all the time or just on start up?Im going to try jumper the  on/off switch on  the 464 and see if that helps.I checked the voltage at the back of the 5v connector on the board and im getting 5.2 volts.As regard to test equipment,unfortunately a multimeter is as far as it goes.

Offline magentis

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Re: CPC-464 blank screen at start up.
« Reply #3 on: 21:19, 27 February 15 »
Hi Bryce,
Thanks for the reply.
I think i will try jumper the on/off switch on the 464 and see if that helps.
I checked the back of the connector on the motherboard and i got 5.2 volts.
Should it beep when the del key is held down all the time or just on start up?
I have checked the monitor settings and i think they are ok.
As regard to test equipment its just a multimeter im afraid.
I thought of a ram fault and was thinking of piggy backing some new IC's on the existing ones,any thoughts on that?
I see a few transistors on the board and i know they can be problematic and was thinking it might be these,but as the cassette appears to be getting power and the ram appears to be getting the correct supply it kinda rules that out.

Offline endangermice

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Re: CPC-464 blank screen at start up.
« Reply #4 on: 22:10, 27 February 15 »
Hi Magentis,

I'm sorry to hear your 464 is not longer working. It could indeed be a RAM fault. Piggybacking the chips can work (I successfully used this technique to troubleshoot a Spectrum +2 a few months ago). However check that none of the chips are running very hot. If they are, it means the chip has an internal short. In this scenario, my experience is that piggybacking wont work so the chip will have to be removed.

RAM is generally the most sensitive component on the board so it is quite lilkely that your issue is due to a RAM problem. Fortunately you have a 464 so there should be 8 RAM chips to replace, so not too bad. You can source new replacements quite easily. Bryce gave me the details of a German company that sells them for a very reasonable price.

Of course the fault with the machine may well lie elsewhere, but the RAM is usually a good place to start once you've eliminated any obvious connection issues e.g. re-socketed chips etc. If you've only got a multimeter, the replace and see approach is probably your best bet.

Sorry I forgot to say, it should beep whenever the del key is pressed.
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Offline magentis

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Re: CPC-464 blank screen at start up.
« Reply #5 on: 22:29, 27 February 15 »
Cheers endangermice,
Thanks for the help.
My 464 doesnt beep at all when the del key is pressed.
I will look into getting some ram IC's and will try that.
The ones in it at the moment do not even get remotely warm,even though they are getting the 5 volt supply.
The only thing that concerns me is the fact they are faulty.
The computer has never had a peripheral connected to it via an edge connector,the only things that have been connected to it are the monitor and a joystick,so i am concerned that it has a power fault that caused the ram to go.
My soldering skills are poor too!So desoldering the existing IC's and soldering on sockets would be beyond my ability.I have tried in the past,with disasterous results to desolder IC's.I think a bad solder sucker didnt help.

Offline Bryce

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Re: CPC-464 blank screen at start up.
« Reply #6 on: 12:11, 28 February 15 »
If you are unsure you can send me the PCB to check it out. The fact that the RAM isn't getting hot doesn't mean that one of them isn't broken. The power on the PCB seems to be fine, so jumpering the power switch probably won't help. It is more likely that some IC has just failed due to age.

Bryce.

Offline magentis

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Re: CPC-464 blank screen at start up.
« Reply #7 on: 02:01, 01 March 15 »
Thanks again Bryce.
I was thinking about this earlier today.
And there is no point really in me getting the ram chips and struggle to replace them,when its quite possibly something else.
I reckon either sending the pcb to someone that knows what they are doing like yourself,or trying to get a known good pcb somewhere would be the sensible thing to do.
This reminds me all too well of a tussle i had with a poorly commodore 16 a few years back.I spent ages on it to no avail.
Replacing part after part in the hope of getting lucky!

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Re: CPC-464 blank screen at start up.
« Reply #8 on: 16:22, 01 March 15 »
I can and I am sure that others will, recommend the Bryce hardware repair service...  :)

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Re: CPC-464 blank screen at start up.
« Reply #9 on: 16:41, 01 March 15 »
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Offline Bryce

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Re: CPC-464 blank screen at start up.
« Reply #10 on: 22:04, 01 March 15 »
Thanks again Bryce.
I was thinking about this earlier today.
And there is no point really in me getting the ram chips and struggle to replace them,when its quite possibly something else.
I reckon either sending the pcb to someone that knows what they are doing like yourself,or trying to get a known good pcb somewhere would be the sensible thing to do.
This reminds me all too well of a tussle i had with a poorly commodore 16 a few years back.I spent ages on it to no avail.
Replacing part after part in the hope of getting lucky!

Blind swapping isn't a good idea, especially at the prices that people are asking for retro custom ICs these days. Obviously it will cost money to send the PCB back and forth, but probably still cheaper than trying to source a new CPC.
I see you're in Dublin. I was in Dublin only two weeks ago, I could have picked it up and saved on postage! Oh well. I won't be back in Dublin until September :(
Did you at least get the C16 fixed? If not, send them both over.

Bryce.

Offline magentis

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Re: CPC-464 blank screen at start up.
« Reply #11 on: 19:12, 02 March 15 »
Thanks Bryce.
I will look into postage and get back to you.

Offline Bryce

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Re: CPC-464 blank screen at start up.
« Reply #12 on: 22:21, 02 March 15 »
I think the postage back to you is about €10, but I'd have to check exactly how long the PCB is including packaging, that it doesn't go above the max length. I think it would be ok though.

Bryce.