Green Screen When Powered-up

[Wobble_master]

Hey and thanks for letting me join. I purchased a CPC464 with Green screen and a bunch of games for a bargin prices over the weekend, had one as a kid and wished I'd never let it go. Anyway's up shot if when it's powered on all I get is a Green Box on the display, from what I have read this seems to indicate a faulty RAM chip, the tape deck fasts forward and rewinds but there are no beeps if you press any keys? I have pulled it all apart and given it a good clean, but is there anything else that I could do while waiting for RAM? Thanks Alex

[abalore]

That doesn't look like a RAM problem to me, it looks either a monitor problem or an ASIC problem. Does it beep when you press the DEL key? Make sure to turn the volume wheel up.

[Wobble_master]

No, nothing happens when you the volume is on and I press Del.

[Rabs]

@abalore , for these cost reduction boards does the ASIC include the 6845 CRTC functionality?       

[abalore]

No, nothing happens when you the volume is on and I press Del.

Next thing you can try is an external diagnostics cartridge, but if you don't want to waste more money, wait for the RAM and cross fingers. If it's the ASIC you'll have a beautiful brick. You can also send the motherboard to me for fixing, just for the cost of shipping and required components.

I'll leave a video on how to use a diagnostics tool:

@abalore , for these cost reduction boards does the ASIC include the 6845 CRTC functionality?     

Yes

[Wobble_master]

Thanks, where can I get the diagnostics cartridge from? I may well take up on the repair if I'm unable to resolve. I have an external power and cable on order to eleminate the screen as being the problem.

[abalore]

Thanks, where can I get the diagnostics cartridge from? I may well take up on the repair if I'm unable to resolve. I have an external power and cable on order to eleminate the screen as being the problem.

here is the hardware:

https://rancanuoteam.com/producto/cpc-mini-dual/

then you can install the diagnostics software as explained in the video.

[Wobble_master]

Excellent, will have a look at this once I have checked the other parts. 

[Bryce]

Hi,
     that looks very much like a dead ASIC. Have you checked the temperature of it? If you have a multimeter or a scope there are some pins you could check to confirm that it's a dead ASIC.

Bryce.

[Wobble_master]

I've checked chip temps and nothing is getting overly warm, I have a multimeter if you can advise on the chips and pins to check that would be fab

[BSC]

@abalore , for these cost reduction boards does the ASIC include the 6845 CRTC functionality?     

I was wondering what you guys were talking about when reading this thread on my mobile phone without being logged in (so I would not see any attachments).. Anyhow, now I am reading from my laptop and can see the images @Wobble_master attached. I think I have never seen a mainboard like the one in the first post. Is IC101 the ASIC you are talking about? What are IC102 and IC103 doing? 

[Wobble_master]

@abalore , for these cost reduction boards does the ASIC include the 6845 CRTC functionality?     

I was wondering what you guys were talking about when reading this thread on my mobile phone without being logged in (so I would not see any attachments).. Anyhow, now I am reading from my laptop and can see the images @Wobble_master attached. I think I have never seen a mainboard like the one in the first post. Is IC101 the ASIC you are talking about? What are IC102 and IC103 doing?

As part of my research for a fix, I only saw 1 other board like this one and they used it to show the variety of revisions, if memory serves its D1. My 1st concern were the 2 black wires, but they showed the same on the other one I saw.

[Wobble_master]

Bit more research on here and it looks like it was the last board produced:

Board: PT NO Z80329, MC0099A, Copyright 1988
MC0099A board fitted with 2x41464 (64Kx4 bits) chips instead of 8x4164 (64Kx1 bit) chips.

https://www.cpcwiki.eu/index.php/Mainboard_Versions

[Wobble_master]

Bit more research on here and it looks like it was the last board produced:

Board: PT NO Z80329, MC0099A, Copyright 1988
MC0099A board fitted with 2x41464 (64Kx4 bits) chips instead of 8x4164 (64Kx1 bit) chips.

https://www.cpcwiki.eu/index.php/Mainboard_Versions

I've just noticed that on the image shown on here of my board there are 2 chips above the RAM, on my board they are missing?

[Wobble_master]

Mine matches this board:

Board: PT NO Z80329, MC0099A, Copyright 1988
Tiny mainboard. Uses 100pin SMD Gate Array (combines the old Gate Array, CRTC, and some FDC/DRAM/RESET logic in one chip).

But has D1 as a revision, the board above has D2

[robcfg]

I've just noticed that on the image shown on here of my board there are 2 chips above the RAM, on my board they are missing?

The board can use either 8x4164 chips or 2x41464 chips as ram options.

Yours obviously is using eight 4164 ram chips, so no missing chips on your board.

[Wobble_master]

Thanks for confirming the board type. 

[Bryce]

I've checked chip temps and nothing is getting overly warm, I have a multimeter if you can advise on the chips and pins to check that would be fab

If you take a look at the GX4000 or CPC+ Schematics you can see the full ASIC pinout and functions. I'd start by checking the CLK signals and then move on to outputs to the DAC. However, before doing any of that, I'd try swapping out the CPU.

Bryce.

[Wobble_master]

I've checked chip temps and nothing is getting overly warm, I have a multimeter if you can advise on the chips and pins to check that would be fab

If you take a look at the GX4000 or CPC+ Schematics you can see the full ASIC pinout and functions. I'd start by checking the CLK signals and then move on to outputs to the DAC. However, before doing any of that, I'd try swapping out the CPU.

Bryce.

've got the schematics to reference pins, just to confirm is this a continuity test with the power on to the board?

Thanks

[Bryce]

I've checked chip temps and nothing is getting overly warm, I have a multimeter if you can advise on the chips and pins to check that would be fab

If you take a look at the GX4000 or CPC+ Schematics you can see the full ASIC pinout and functions. I'd start by checking the CLK signals and then move on to outputs to the DAC. However, before doing any of that, I'd try swapping out the CPU.

Bryce.

've got the schematics to reference pins, just to confirm is this a continuity test with the power on to the board?

Thanks

No, you should check if any voltage or signal is present on each pin while the CPC is running.

Bryce.

[Wobble_master]

Thanks, will be the weekend now. 

[Wobble_master]

No, nothing happens when you the volume is on and I press Del.

Next thing you can try is an external diagnostics cartridge, but if you don't want to waste more money, wait for the RAM and cross fingers. If it's the ASIC you'll have a beautiful brick. You can also send the motherboard to me for fixing, just for the cost of shipping and required components.

I'll leave a video on how to use a diagnostics tool:

@abalore , for these cost reduction boards does the ASIC include the 6845 CRTC functionality?     

Yes

@abalore , I have a Dandanator on order if I get nothing from this I'd like to take you up on the repair as I could spend a fortune on just replacing parts, and tools to do so.

[abalore]

No, nothing happens when you the volume is on and I press Del.

Next thing you can try is an external diagnostics cartridge, but if you don't want to waste more money, wait for the RAM and cross fingers. If it's the ASIC you'll have a beautiful brick. You can also send the motherboard to me for fixing, just for the cost of shipping and required components.

I'll leave a video on how to use a diagnostics tool:

@abalore , for these cost reduction boards does the ASIC include the 6845 CRTC functionality?     

Yes

@abalore , I have a Dandanator on order if I get nothing from this I'd like to take you up on the repair as I could spend a fortune on just replacing parts, and tools to do so.

perfect, will send you a PM

[McArti0]

60Hz set.... maybe

@Wobble_master have You oscilloscope or multimeter ?

[abalore]

60Hz set.... maybe

@Wobble_master have You oscilloscope or multimeter ?

We already stated that the unit doesn't beep when DEL key is pressed after turning on, so it's something more than just the bad image.