As a supplement in case it helps anyone else. I have a DSP5200C that had been working fine for years and then developed a badly flickering display. Thought it might be power and did the usual experiments to isolate. Removed all cables other than power. Tried other sockets. Moved the speaker, etc. Ended up taping a layer of aluminum kitchen foil on the shelf above and below the speaker which has fixed it. I live in an apartment in NYC and speculation is that it was picking up RF interference from a neighbors wifi hotspot. An experienced and wise friend suggested getting an inductor choke for the internal cable which I will be exploring next, but in the meantime, no display flicker. Hope that helps anyone with a similar ghost in the machine.