SC504 Trace Shadow

Barry Breaux All Messages By This Member #208354 Greetings, What would cause this? Thank you! /g/TekScopes/photo/300558/3883505?p=Created%2C%2C%2C20%2C2%2C0%2C0
David C. Partridge Member Profile All Messages By This Member #208355 I think the SC504 use a expansion mesh PDA. I that's the case, if you turn the brightness up to high levels you will get that effect. David toggle quoted message Show quoted text -----Original Message----- From: [email protected] <[email protected]> On Behalf Of Barry Breaux Sent: 07 February 2025 16:55 To: [email protected] Subject: [TekScopes] SC504 Trace Shadow Greetings, What would cause this? Thank you! /g/TekScopes/photo/300558/3883505?p=Created%2C%2C%2C20%2C2%2C0%2C0
n4buq All Messages By This Member #208357 Looks like the FOCUS control knob and shaft is missing. That might also contribute to a bit of that as well, correct? Thanks, Barry - N4BUQ toggle quoted message Show quoted text I think the SC504 use a expansion mesh PDA. I that's the case, if you turn the brightness up to high levels you will get that effect. David -----Original Message----- From: [email protected] <[email protected]> On Behalf Of Barry Breaux Sent: 07 February 2025 16:55 To: [email protected] Subject: [TekScopes] SC504 Trace Shadow Greetings, What would cause this? Thank you! /g/TekScopes/photo/300558/3883505?p=Created%2C%2C%2C20%2C2%2C0%2C0
Barry Breaux All Messages By This Member #208358 Hello N4BUQ, I removed the knob and shaft in order to more easily probe the transistors under the shaft. I can still adjust the focus. Thanks, Barry
Barry Breaux All Messages By This Member #208359 David, Thanks for your comment! No matter how low I turn down the Intensity you can still see this shadow. (Until both the trace and shadow go undetected.) Barry
Ozan All Messages By This Member #208384 On Fri, Feb 7, 2025 at 08:54 AM, Barry Breaux wrote: Greetings, What would cause this? Thank you! /g/TekScopes/photo/300558/3883505?p=Created%2C%2C%2C20%2C2%2C0%2C0 Scope seems to be in "chop" mode based on the position of "Display" knob. Are you applying the same signal to both channels? You could be seeing Ch1 and Ch2 together, I see that triggering is on Ch2, and Ch1 and Ch2 gains are not the same (Ch2 red knob is also out of cal position). If you switch coupling to GND for one of the channels, pick trigger and input source for the active channel, do you still see two waveforms? Ozan
Barry Breaux All Messages By This Member #208398 Ozan, Select CH1 OR CH2 and trace shows CH2. I currently have a square wave going to CH1 AND A sine wave going to CH2. Regardless of the switch position CH2 is displayed. (Except when CH1-CH2 is selected. The trace reflection is there all the time to some extent. Decreases with intensity. Thanks! Barry
Ozan All Messages By This Member #208399 Hi Barry, Nice find with delay line. Just to make sure it is Ch2 and not the trigger path showing up on screen for some reason, if you change trigger source to Ch1/Ch2 does anything change? Are collector voltages of Q1455 and Q1555 same as before after delay line fix? I assume pin 3 voltage of the hybrids will be different now, any change to pins 3,4,5,16,17 on CH2 hybrid after delay line fix? It is possible Ch1 is visible but it is off the screen and bouncing off the CRT wall giving you ghost image. Does moving Ch1 Y offset knob change anything? What are the voltages of pin 16 and pin 17 (gives an idea about channel DC level) on Ch1 hybrid? Pins 3,4,5 are shared with Hybrid 2 so they will be the same as Hybrid 2 voltages. Ozan toggle quoted message Show quoted text On Mon, Feb 10, 2025 at 10:56 AM, Barry Breaux wrote: Ozan, Select CH1 OR CH2 and trace shows CH2. I currently have a square wave going to CH1 AND A sine wave going to CH2. Regardless of the switch position CH2 is displayed. (Except when CH1-CH2 is selected. The trace reflection is there all the time to some extent. Decreases with intensity. Thanks! Barry
Barry Breaux All Messages By This Member #208400 Just to make sure it is Ch2 and not the trigger path showing up on screen for some reason, if you change trigger source to Ch1/Ch2 does anything change? **Nothing changes when switching between CH1 and CH2. Are collector voltages of Q1455 and Q1555 same as before after delay line fix? Here is what they are now... CH 1 Selected Q1455 E=-0.680 B=-0.047 C=0.649 Q1555 E=-0.680 B=0.000 C=1.160 CH 2 Selected Q1455 E=-0.681 B= 0.277 C=0.366 Q1555 E=-0.681 B=0.000 C=1.047 I assume pin 3 voltage of the hybrids will be different now, any change to pins 3,4,5,16,17 on CH2 hybrid after delay line fix? CH 1 Selected Pin 3=+2.718 Pin 4=+2.754 Pin 5=+1.722 Pin16=-0.844 Pin17=-0.841 CH 2 Selected Pin 3=+2.721 Pin 4=+2.721 Pin 5=+1.722 Pin16=-0.846 Pin17=-0.838 It is possible Ch1 is visible but it is off the screen and bouncing off the CRT wall giving you ghost image. I don't think so. I have a square wave on CH1 and a Sine wave on Channel 2. Does moving Ch1 Y offset knob change anything? There is a slight jitter in the trace when CH1 position is 100% fully clockwise. The jitter goes away at 99% fully clockwise. What are the voltages of pin 16 and pin 17 (gives an idea about channel DC level) on Ch1 hybrid? Pins 3,4,5 are shared with Hybrid 2 so they will be the same as Hybrid 2 voltages. CH1 Hybrid with CH 1 Selected Pin16=-0.871 Pin17=-0.805 **CH1 Hybrid with CH 2 Selected Pin16=-0.871 Pin17=-0.805 Checked and doubled checked. Seems like the voltages varies a bit during each test cycle. Thanks for looking at this. I am learning a lot, but a ways to go Barry
Barry Breaux All Messages By This Member #208401 Just to make sure it is Ch2 and not the trigger path showing up on screen for some reason, if you change trigger source to Ch1/Ch2 does anything change? **When I change the trigger from CH1 to CH2 it does change. If in CH2 the Sine Wave becomes synchronized as it should. If I switch the trigger to CH1 it shows the CH2 Sine Wave but it is NOT synchronized. Nothing changes when switching between CH1 and CH2. Are collector voltages of Q1455 and Q1555 same as before after delay line fix? Here is what they are now... CH 1 Selected Q1455 E=-0.680 B=-0.047 C=0.649 Q1555 E=-0.680 B=0.000 C=1.160 CH 2 Selected Q1455 E=-0.681 B= 0.277 C=0.366 Q1555 E=-0.681 B=0.000 C=1.047 I assume pin 3 voltage of the hybrids will be different now, any change to pins 3,4,5,16,17 on CH2 hybrid after delay line fix? CH 1 Selected Pin 3=+2.718 Pin 4=+2.754 Pin 5=+1.722 Pin16=-0.844 Pin17=-0.841 CH 2 Selected Pin 3=+2.721 Pin 4=+2.721 Pin 5=+1.722 Pin16=-0.846 Pin17=-0.838 It is possible Ch1 is visible but it is off the screen and bouncing off the CRT wall giving you ghost image. I don't think so. I have a square wave on CH1 and a Sine wave on Channel 2. Does moving Ch1 Y offset knob change anything? There is a slight jitter in the trace when CH1 position is 100% fully clockwise. The jitter goes away at 99% fully clockwise. What are the voltages of pin 16 and pin 17 (gives an idea about channel DC level) on Ch1 hybrid? Pins 3,4,5 are shared with Hybrid 2 so they will be the same as Hybrid 2 voltages. CH1 Hybrid with CH 1 Selected Pin16=-0.871 Pin17=-0.805 **CH1 Hybrid with CH 2 Selected Pin16=-0.871 Pin17=-0.805 Checked and doubled checked. Seems like the voltages varies a bit during each test cycle. Thanks for looking at this. I am learning a lot, but a ways to go Barry
Ozan All Messages By This Member #208403 Hi Barry, If you look at hybrid schematic on TekWiki pin 1 is the mid point of a 845-ohm to ground and 1.21k to +5V. In your measurement Ch2 hybrid shows ~ 0.366-0.649V at pin 1. This means a current on the order of 4mA is pulled from pin 1 (assuming hybrid is good). Nothing around Q1455 should be able to pull this much current (resistors are too large to support 4mA) in normal operation except CR1457 in Trigger View, even then 0.366V looks low. If you exercise “Trig View” switch does anything change? In 1-2 or 1+2 modes do the voltages at collectors of Q1455 and Q1555 change? In this mode emitter currents are removed, transistors shouldn’t be able to pull pin1 lower. Most likely collector of Q1555 will go to 2V, this would enable Ch1 to be displayed. Likely you will find collector voltage of Q1455 still low. Assuming collector of Q1455 won’t go to 2V even in 1-2 or 1+2 modes, does lifting one leg of CR1457 change collector voltage of Q1455 to 1 to 2V range in 1-2 or 1+2 modes? Could there be a solder bridge or some kind of short on pin 1 node of Ch2 hybrid? If both Q1455 and CR1457 is removed and pin 1 is still not at 2V hybrid is suspect. As a side note 0.7V at pin1 should have disabled Ch2 as well. I don’t see why Ch2 is displayed with pin1 below 1.5V. Ozan toggle quoted message Show quoted text On Tue, Feb 11, 2025 at 02:11 PM, Barry Breaux wrote: Just to make sure it is Ch2 and not the trigger path showing up on screen for some reason, if you change trigger source to Ch1/Ch2 does anything change? **When I change the trigger from CH1 to CH2 it does change. If in CH2 the Sine Wave becomes synchronized as it should. If I switch the trigger to CH1 it shows the CH2 Sine Wave but it is NOT synchronized. Nothing changes when switching between CH1 and CH2. Are collector voltages of Q1455 and Q1555 same as before after delay line fix? Here is what they are now... CH 1 Selected Q1455 E=-0.680 B=-0.047 C=0.649 Q1555 E=-0.680 B=0.000 C=1.160 CH 2 Selected Q1455 E=-0.681 B= 0.277 C=0.366 Q1555 E=-0.681 B=0.000 C=1.047 I assume pin 3 voltage of the hybrids will be different now, any change to pins 3,4,5,16,17 on CH2 hybrid after delay line fix? CH 1 Selected Pin 3=+2.718 Pin 4=+2.754 Pin 5=+1.722 Pin16=-0.844 Pin17=-0.841 CH 2 Selected Pin 3=+2.721 Pin 4=+2.721 Pin 5=+1.722 Pin16=-0.846 Pin17=-0.838 It is possible Ch1 is visible but it is off the screen and bouncing off the CRT wall giving you ghost image. I don't think so. I have a square wave on CH1 and a Sine wave on Channel 2. Does moving Ch1 Y offset knob change anything? There is a slight jitter in the trace when CH1 position is 100% fully clockwise. The jitter goes away at 99% fully clockwise. What are the voltages of pin 16 and pin 17 (gives an idea about channel DC level) on Ch1 hybrid? Pins 3,4,5 are shared with Hybrid 2 so they will be the same as Hybrid 2 voltages. CH1 Hybrid with CH 1 Selected Pin16=-0.871 Pin17=-0.805 **CH1 Hybrid with CH 2 Selected Pin16=-0.871 Pin17=-0.805 Checked and doubled checked. Seems like the voltages varies a bit during each test cycle. Thanks for looking at this. I am learning a lot, but a ways to go Barry
Edward Prest All Messages By This Member #208404 I see some type of conic beam expansion going on. The gost image is larger in both the x and y direction. Guessing it's crt (acceleration) related. I would check every bias voltage going to the tube, focus, ripple etc.
Barry Breaux All Messages By This Member #208407 Ozan, I took both of the hybrids out for inspection. I found an open trace on Pin1 and Pin2 of the hybrid that was installed on channel 2. I tried to repair the trace but ended up damaging several other traces. I don't think I can fix those. History here is that I had swapped Ch1 Hybrid and Ch2 Hybrid expecting the symptoms to switch, they didn't. I did this several days before I asked for help. I wonder if the scope would have worked with the open traces in the hybrid 1 slot as original. The part numbers on both hybrids are the same, but the open circuits look intentional. I also found a defect on one of the rubber band contacts, Contact #8. These switches are a bad design. I have another SC504 on order. Thanks for your help. This project is on hold for now! Barry
Barry Breaux All Messages By This Member #208408 Edward, First off thanks for your comment. This scope has other issues right now. I need to understand more about crt acceleration. But will go through a full calibration if I can get everything else fixed. Thanks! Barry

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SC504 Trace Shadow