Re: 7704A bottom readout out of position

Thierry Delaitre

Thanks Mark/Craig

I've removed the vertical units in order to check the centering. I've
adjusted R93 on the vertical amplifier for the trace to be in the center.

It has slightly improved the readout but it seems the bottom character line
is still slightly too high. If it try to adjust the vertical separation,
then the linearity for the top and bottom appear to be different. The top
line disappears the screens a lot faster than the bottom one.

I've checked the resistors around the output of the X&Y of U3480 and all
appear to be ok. R84 to R99.

I attach a picture of the screen. Should I expect the bottom line to be
lower ?



On Fri, Aug 2, 2019 at 7:25 AM Craig Sawyers <>

The bottom readout line on my 7704A appears to be out of position and
has gone up - it is located at
one third of the screen from the bottom. The one at the top is ok and
well positioned. I tried to
the vertical separation pot but if I use it, then the top line goes up
outside the CRT. I've
replaced the
tantalum capacitors on the readout board and the voltages appear to be
spot on. do you know what I
could try to troubleshoot?
Apart from the occasional dead readout chip (which has much more obvious
problems) I once had a
resistor on the readout board go open. Very odd since it looked like metal
film - but worth checking
on yours.


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