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 Post subject: Re: Heath 100-203-31 oscope clock conversion
PostPosted: Apr Mon 30, 2018 8:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 19926
Location: Warner Robins, GA
For probing the signals I used a scope set to X/Y mode and two 10X probes so I could see the clock face.

After some probing the signal looks fine going into the OP-AMP and coming out of the OP-AMP.

The signal on the deflection transistor collectors however is not fine at all.

Viewing the clock face on a scope from the transistor collectors shows it has some geometry issues even with the deflection plate leads disconnected including showing the beam as it moves between the lines that are supposed to be drawn.

At first I though it was the deflection plate leads, but I did run regular non-shielded wire to the vertical and horizontal position controls so maybe that is the problem.

Now if I do swap to shielded wire is it ok to make the shield connect to the -5volt line or should it be grounded and a separate shielded wire used for the -5 volt connection to the position pot?



EDIT:

I got the focus to be nearly perfect and I got the expanding of the image to stop when I turened up the intensity.

Had to add a 220K resistor between the intensity pot and cathode then add a .005uF cap from cathode to ground.

The focus consists of a 200K resistor in series with the 1 meg potfrom the B- CRT voltage then a 1 meg resistor to ground from the other end of the pot. The original pilot light was a neon bulb and was fed from the 150Vdc supply so I tried it in series with the 1 meg resistor and it lights just fine and also serves as an indicator that the CRT HV is present.

The wiring from the position pots to the board was replaced with shielded wiring which I think helped some of the geometry issues.

What's odd is I can feed the Tektronix scope I am using to check the clock display from the clock board or the output of the OP-AMPs and the displ;ay looks great with barely visible retrace lines.

Now if I feed the scope with the signal from the deflection transistors with or without the deflection plates connected, the display doesn't look nearly as clean and now there's visible retrace lines which are nearly as bright as the regular displayed lines.

Now could the position pots being away from the board be causing the issue?


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 Post subject: Re: Heath 100-203-31 oscope clock conversion
PostPosted: May Mon 07, 2018 8:15 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 19926
Location: Warner Robins, GA
Well the intensity, focus and deflection are nearly perfect.

I have just one issue that I have no clue as to why it is happening.

Using two 10X probes and a Tektronix 2246 scope as the display I see a perfect clock display from the clock board with barely visible if not any retrace lines. I get the same at both the inputs and outputs of the TL-082 OP-AMP. In fact the signals are so good at the output that I can connect one channel to the clock board and the other to the OP-AMP out and still get the same perfect display.

If I connect to the deflection outputs even with the deflection plates disconnected I get retrace lines on the 2246 scope as though the phosphor doesn't have a short enough persistence and is what I would expect to see with a low bandwidth scope and is something the retrace blanking circuit cant properly deal with as nothing I have done has properly blanked the lines without blanking some of the display that is supposed to be shown. The geometry is nearly perfect though.

I am at a complete loss as to how the deflection amp stage could be causing the issue.

Only thing I can think of is the position controls are on the front panel and I use decent shielded wire to connect then to the board.

Could that somehow be affecting the deflection amp stage?


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