CFXII - Black screen with it plugged in

About original Memotech hardware.
acsi
Posts: 31
Joined: 16 May 2019 08:49

CFXII - Black screen with it plugged in

Post by acsi »

Hi

Got the MTX out today and found that I get No Signal (according to the monitor) through the VGA and black screen on the Composite output.
Tested the Monitor and VGA cables with a known working source OK
Unplugged the CFX and get the Ready prompt and cursor through the Composite output.

Anyone have any ideas what the issue could be? Or where to start looking?

Thanks in advance

Mike
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Dave
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Re: CFXII - Black screen with it plugged in

Post by Dave »

Hi Mike

I’d start by giving the computer board edge connector a good clean, including the underside (which is not that easy).

With the internal version of CFX-II, there should be a locating key in position 5 of the edge connector plug, make sure that is there and the board is aligned with the proper pins on the PCB.

Try removing & reseating the CFX-II chips.

Try booting with the CFX-II attached but with the ribbon cable disconnected from the board.

If those simple steps don’t help, I’m afraid that it may be a failed chip on the CFX board

Regards
Dave
Martin A
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Joined: 09 Nov 2013 21:03

Re: CFXII - Black screen with it plugged in

Post by Martin A »

I'll echo what Dave put, Memotech's penny pinching on the edge connectors has been a source of grief from the 80's onward.

Poor contact between the MTX and expansions causes most of the start-up problems I see from my own MTX. (and lucky for me the MTX here usually has both internal and external expansions connected, either or both of which could be the culprit!)
acsi
Posts: 31
Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

I tried with the CF card removed and have verified the Rom.

I'll open it up again tomorrow and clean the edge connector and reseat the chips.

Thanks
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Dave
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Re: CFXII - Black screen with it plugged in

Post by Dave »

OK, let us know how you get on.

(I meant that you should disconnect the card reader, not just remove the card, on the off chance that a reader module fault could cause issues if it’s not the edge connector.)

Regards
Dave
acsi
Posts: 31
Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

Sorry I meant I had removed the CF adapter not just the card itself :lol:

Edit: I have tested with the Magrom fitted internally and it works however I have found I do not get any sound with it mounted internally or externally?
CFXII is still not working.

I think maybe its a power issue? Caps?

Are there any points I should get a certain voltage? PSU tests correctly at the plug.
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Dave
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Re: CFXII - Black screen with it plugged in

Post by Dave »

This page might be helpful for voltage measurement points . . . .

http://www.primrosebank.net/computers/ ... mtxpsu.htm

With no add on boards connected, do you get any sound output?

(With no software running, from BASIC, hitting <Ctrl><g> should give a “ding”)

Regards
Dave
acsi
Posts: 31
Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

Thanks Dave,

No sound with CTRL + G. I notice that if I tap or nudge the video board the display changes to Grey. I will check the solder contacts and replace the caps on the motherboard at least as the Axial cap which goes over the regulators looks incorrect (2200uF 63v) and isn't wired up the best anyway (could short to the frame).

Image

Thanks
Mike
Martin A
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Re: CFXII - Black screen with it plugged in

Post by Martin A »

From that photo C53 appears to be missing, and the ground wire for the audo?? output has com adrift. The video and audo grounds appear from the schematic to be connected, so it probably isn't anything to do with the missing sound issue. But a flapping wire inside a metal case is never good!

Contrary to what the schematic in the manual shows, both large capacitors should be 4700uf. Memotech fitted 16v versions, but a 25v rating would be more approriate, especially for C51 as the AC input is a nominal 18v.

C53 would be 470uf, again the schematic says 16v but i replaced mine with a 25v part when it failed.
acsi
Posts: 31
Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

Whilst waiting for the caps to arrive I connected the floating ground and put in a ground strap. Still no audio. Will be interesting to see if the caps help.

Also with the missing c53 on the list it shows as being a 100uF but Martin you mention a 470uF?
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