Fixing the Issue 4 Spectrum (part 2)

After checking the power rails it was obvious that the 5v regulator wasn’t working, so first action was to replace it.

With the regulator replaced I hopefully tried the power again.  This time all the power rails looked good, but still no picture. After checking with my multi-meter and oscilloscope everything looked good.  Clock signals fine, memory address and data lines ok , ULA video output ok…..  I was at a bit of a loss.

While thinking the problem over I decided to apply the composite video mod in the hope that when it did work at least it would look better.

Composite video mod

With that completed, I plugged in once again to started diagnosing the problem, and surprise …. I had a picture.  So the problem must be with the analog video out.  

I wasn’t out of the woods yet, I had the typical memory fault colour bars on boot.  Using my new diagnostics cartridge quickly identified the two upper DRAM chips that were to blame.

Just a couple of upper memory faults…

The upper DRAM was already socket-ed making replacing very easy.

Fixed Spectrum 48K

With the fix complete it was time to play some games 🙂

Game time

Still some cosmetic fixes, but that’s a later post.

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