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#136
09-04-2024, 11:03 AM
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Yes, you absolutely would get a signal if you bet a cap between the scope probe and the circuit you are probing. That's the same as putting your scope in AC coupling mode.
"I grounded the scope input by attaching the scope input to the same point." I don't understand that statement. You should not be grounding the scope input. I think be are mixing up terms here. The scope PROBE should always be grounded. That's the black clip. It goes to the chassis. The scope probe tip goes to the test point. You don't need a 1,000 pF cap anywhere for anything. You wrote "I have the scope probe grounded through a 1000pF capacitor". That would mean the black clip on the scope probe would be connect to one end of a cap and the other end of the cap would be going to the chassis. That is not what you show in the picture. The scope trace should look better than that. Unless it's your camera making it look faint and smeared. Here's an "S" curve from a similar chassis on a 350MHz bandwidth analog scope with no bandwidth filtering. 
Last edited by bandersen; 09-04-2024 at 11:06 AM. 
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#137
09-04-2024, 11:27 AM
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Dear god...so embarrassing. I thought we had talked previously talked about using a 1nF cap in this manner. My bad. Yes the probe is grounded through the scope clip to the chassis and the probe is connected to the test point. I'll get rid of the capacitor. I don't know what I'm doing wrong. 10 pages of instruction, mentoring, buying equipment, suggestions, fixes, double checks and triple checks and still crap on the scope. Maybe I'll change the 6AL5 and see if that does anything. The instruction says connect the scope probe to the junction of C183 and R203. Isn't that pin 5 on the 6AL5 or do I have this wrong too?
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#138
09-04-2024, 11:50 AM
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Assuming that this is not hot chassis, and / or things are isolated, you could try a secondary ground wire to the chassis to the o-scope, don't rely on the probe ground alone, I have to do this at work often, and I have never seen a scope that did not have alt ground points on it that could be used for such things.
__________________
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#140
09-04-2024, 12:03 PM
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You do not have crap on your scope. What volts/div is your scope set to? I think it may simply be you need to feed a stronger signal into the scope.
You should also terminate the end of the RF out cable. I assume with 50 ohms. The original RF out cable likely had a termination pod with little alligator clips. Or maybe there's something wrong with the scope. Does it produce a sharp bright line when there is no signal?
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#141
09-04-2024, 12:23 PM
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Out of XY mode I have 2 sharp lines for both channels 1 and 2. I cant tell what V/Div I'm using on the horizontal because the scale wheel is broken off of that adjustment. When you say RF termination and 50 ohms, do you mean put a 50ohm resistor between the RF clip lead and pin 1 of V117
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#142
09-04-2024, 12:34 PM
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Volts/div vertical. RF clip lead and ground.
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#143
09-04-2024, 12:44 PM
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Quote:
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#144
09-04-2024, 01:06 PM
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Yes. Think about it this was. Your RF out is like a radio transmitter. Without a load at the end, the RF is going all over the place including being reflected back into the generator.
Every work on a ham transmitter or hear of a dummy load? You're probably too young to remember token ring computer networks or you'd be all too familiar with termination. I just solder a 47 ohm resistor between the test clips Here are some ancient ones.  
Last edited by bandersen; 09-04-2024 at 01:22 PM.
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#146
09-04-2024, 01:23 PM
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The broken scale wheel is an annoyance but by no means a stop, you should be able to work out what the sets are using the other channel, since it's a dual scope, every scope has a calibrate output for the probe, set everything to the calibrated point, and with both channels showing, set the non broken one to any arbitrary input level 5,10, 2v what ever, hook that input to the calibrate probe output, note how many steps it shows on the screen (scale), change to the broken side, switch around till it matches, you have found that setting that the non broken one is set to, mark it with some kind of permanent marker, you now have a known start point to where you can count to the other settings.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#147
09-04-2024, 01:27 PM
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I think you have an EICO 369? It has one built into the output lead as shown in this diagram.
Now let's be clear - you will still get RF output without this resistor. You can still do an alignment without this resistor. However, the get the best results (and keep your generator happy) you should use one. It will also mean your output level meter should be accurate, Notice there is also a resistor and 1,000 pF capacitor inside the demodulator probe. That's what Pentode was talking about adding. It's a low pass filter and will help remove noise if you have a fuzzy trace. I'm not sure based you your scope screenshots if that's really what your trouble is. 
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#148
09-04-2024, 01:42 PM
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Quote:
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#149
09-04-2024, 01:50 PM
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Bob
On the old WO33A you show, is the probe you are using a WG-349A probe? No demod in it, but is it a form of 10-1 modern day scope probe?
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#150
09-04-2024, 01:55 PM
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Quote:
Seen them before, not sure what you call those old type RF jacks :O
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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