BoborAnn said:
I have this DAT tape unit that is rarely used when I tried it yesterday it
ran fine but the display was entirely dark. Tape runs and I get audio out.
Opened it up and saw nothing obvious. Hoping somebody has seen this and
can advise where to start
Thanks in advance
Bob
I think that this unit uses a VFD. You can easily identify one of these.
It's flat, glass, has an evacuation pip, a single row of pins along the top
edge, all equally spaced, except for the last two at the left and right
ends, which have an extra space. Thes 4 pins are the device heater
connections - each is a parallel pair so the heater is connected between the
left two end pins, and the right two. There should be about 2 to 4 volts AC
across these pins, and measuring from ground to either pin pair should give
you about -30v DC, as the heater is floated on a negative 30v supply to keep
it at about the same potential as the segment drives.
It's very common for the -30v supply to fail, usually due to dried out
electrolytic caps. Also, with some models using this type of display, there
is a small picofuse, or safety resistor in series with the heater feed.
These often fail for no apparent reason.
Arfa