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Old 21st Nov 2018, 4:57 am   #6
Noopy2014
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Join Date: May 2014
Location: Eichstätt, Germany
Posts: 88
Default Re: Gould 407x display help

I agree with Chris.
You don´t have a problem with the brightness. You have a problem with a noise on the Y-axis. The lines consume the brightness which should power up only small dot.

But the interesting question is: Where does that come from?

I would suggest the following:

1. Measure the voltage between the plate Y1 and ground and Y2 and ground directly at the base of the CRT.
You should see whether both plate potentials are ok.
If it´s so you have aproblem with your CRT. I don´t know a way to missaligne the CRT in such a way so there could only be a broken Joint in the CRT. If it´s so I would have one in stock.

2. If there is a noise on the Y-deflection it gets more interesting.
The supply for the deflection amplifier supplys first the Y-amp than the X-amp. Noise on the supply should be visible on both deflections which we don´t see.
There could be a defect in the Y-amp. But I would first try to test whether there is a problem with the small signal coming to the Y-amp. That´s a bit tricky because it´s a differential current interface. Best way is to activate the external plotter an measure the signal on the plotter interface at the backside of the 4070. This signal is picked up between the Y-DAC and the Y-amp. Strange signals at the plotter interface would lead to the display card. I would suggest to display one grounded channel so you should see a single value for a longer period. If it´s a mess and not a value...
In the end you need either a new DAC08 or you have to do a logic search or you have to do a more ugly search in the SMD-Y-Amp but let´s see what you get. Edit: There could also be a connector problem...

Of course I have some spare parts here...

Best regards,

Richard
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