Re: Tek 7603 missing readout but present when beam finder pressed


Roger Evans
 

Roy,

If adjusting R2291 does not solve the problem then there are a couple of other tests that would help to tie down the fault, don't yet adjust R403 on the vertical amplifier board.

Remove both vertical amplifier plugins and leave the time base plugin in place, set to auto-trigger. Turn the scope on and you should see a horizontal trace very close to the centre of the CRT. If it is more than a couple of minor divisions out it will need resetting later, if it is seriously out then it may indicate a fault in the vertical amplifier.

Replace the vertical plugins with no input signals and arrange the display to have two horizontal lines, if you have a dual trace plugin then use both sections of the one plugin, this will activate an upper and a lower readout slot. Set the upper line to one division below the top of the screen and the lower line to one division above the bottom of the screen. Now press the beam finder and turn the readout intensity up so that you can see the compressed readout. Where are the compressed readouts relative to the two traces?

When you said that the scope was working fine apart from the lack of readout, had you checked with a ramp or sawtooth waveform that there is no distortion in the vertical signal? If you don't have a suitable waveform generator then check that a two division square wave does not change amplitude as you move it up and down the display. It is always possible that a previous owner has tried to adjust out a vertical deflection fault using R403 and moved the readout off screen in the process.

Jeff, the readout signal is single ended, not balanced like the main Y signal, but it should move symmetrically about ground provided the components and ICs on the readout board have not drifted over time. Other 7000 scopes like the 7904 do have a preset control on the vertical amplifier board to centre the readout separately from the main Y signal.

Regards,

Roger

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