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
Unfortunately its not that simple this is one of those with a blue display that can be partially turned off (air only the level meters remain on) which would rule out a lamp 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.
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