Jim wrote:
On Sep 23, 8:14 pm, 1PW wrote:
What is the exact output rating on the power supply. Please quote
accurately.

--
1PW

The power supply:
Input: 240V 50Hz
Output: 5V, 1.5A, 7.5VA
PIN 4, 1, 6: +5V
PIN 5, 3, 7: Gnd

(The plug is a 7 pin din)

Excellent Jim. Large value electrolytic filter capacitors are
probably inside your power supply. Their aging may have brought about
an A.C. ripple component in the otherwise +5VDC output.

If you have any large electrolytic capacitors around the home that
could be connected temporarily across pins 4&5 or 1&3 or 6&7, (observe
the correct polarity) in the appropriate manner, you might be able to
isolate the trouble to the power supply. The caps should have a
working voltage of 5 volts or higher and be as large as you can find
for now.

Even putting a multimeter across those same DIN pairs of pins while
the meter is set to measure A.C. would let you know if you have too
much unfiltered A.C. ripple on the D.C. output.

Being able to open up the power supplies might be difficult if they
have been glued shut as some were back then. Your observations that
things seem to improve as you allow time to elapse while looking at
the video tells me that the capacitors are try to "reform" but their
age has allowed them to leak too much.

HTH

--
1PW