I have a Tektronix TDS220 oscilloscope that has developed this
intermittent startup fault:

Sometimes when the power is switched on the LCD will only show a random
number of horizontal dark/brihter lines of random widths. The LCD
backlight will not be turned on and the mainborad doesn't appear to be
working as there will be no 1KHz/5V square wave on the compensation
probe output. Also the GPIB interface will not be working. After I reset
the mainboard (switch off and on the oscilloscope) several times I
eventually manage to get it started and the oscilloscope will work fine
for then on, until it is switched off. So I suspect this might be
related to a power on reset function (firmware) not being called
properly at the startup or maybe some dodgy power supply connection to
the main board. I wonder if anyone has had a similar problem and/or
could provide some insight about what might be causing this problem.
Tektronix UK will charge £425 + VAT (US$775 + tax) to fix it and will
take nearly 1 month (apparently they have to be sent to Germany to be
repaired). Thanks.

Tony