Display issue on rev 6A motherboard with DIVMMC Future

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Vyprman
Posts: 5
Joined: Thu Nov 29, 2018 11:18 pm

Display issue on rev 6A motherboard with DIVMMC Future

Post by Vyprman » Sun Dec 02, 2018 3:27 pm

I have a rubber key spectrum which I have been restoring.
I received the system along with a ZX81 and a +3 model both of which have now been restored to full working order and I thought I had done hte same with the rubber key model.

The machine has had capacitors replaced, a new keyboard and membrane and a new metal backplate for the keyboard as the old one was dinged to hell and back and peeling off. I also performed the capacitor od for the modulator to allow composite video.

I then bought a DivMMC Future direct from TFW8B and am seeing an odd issue.

Basically when the unit powers on I get a normal display, when the DivMMC is activated, the display gradually dims, the picture is still visible and I can load and run software but the display is very dark.

Thinking it was a power issue, I replaced the 7805 regulator and the PSU with new versions but still seeing the same issue.

Where would be the best place to start troubleshooting?

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1024MAK
Posts: 2162
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Display issue on rev 6A motherboard with DIVMMC Future

Post by 1024MAK » Mon Dec 03, 2018 5:19 am

My best suggestion is to test the voltage on the 12V rail while the symptoms are present.

Mark

Vyprman
Posts: 5
Joined: Thu Nov 29, 2018 11:18 pm

Re: Display issue on rev 6A motherboard with DIVMMC Future

Post by Vyprman » Sat Dec 08, 2018 5:33 pm

Looks like it was the DC Barrel connector, I swapped it from another Spectrum that is undergoing repairs and the display stays birght.. I suspected the barrel because the system would not power on properly if the Adapter was plugged all the way in.
New barrel has been ordered and added to the list of bits needed to fix the other board.

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1024MAK
Posts: 2162
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Display issue on rev 6A motherboard with DIVMMC Future

Post by 1024MAK » Sat Dec 08, 2018 10:53 pm

Good that you have found the problem :D

And thanks for letting us know what you found.

Mark

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