I'm not sure if what I'm seeing is the hybrid chip failure or not, but for the life of me I can't seem to get a horizontal sweep (entirely possible this is user error). Everything else seems to work, I get a dot on screen, display works fine, I can adjust manually horizontally and vertically and the cursors (both T and V) work. I haven't used this scope in a decade and wanted to rule anything obvious out before I start tearing it apart. I followed the manual details to get a baseline, but no scan
Thanks
Welcome to the forum.
Check it is not set to XY mode.
I don't think so. I've got the Sec/Div switch set to 100ms locked
I'm not sure if what I'm seeing is the hybrid chip failure or not, but for the life of me I can't seem to get a horizontal sweep (entirely possible this is user error). Everything else seems to work, I get a dot on screen, display works fine, I can adjust manually horizontally and vertically and the cursors (both T and V) work. I haven't used this scope in a decade and wanted to rule anything obvious out before I start tearing it apart. I followed the manual details to get a baseline, but no scan
Can you post a clear photo of the front of the scope as this happens? We should be able to spot any user errors that way.
Here you go. I also ran the self test and it comes back clean
I see the problem, it's upside-downish!
It looks like it's not user error. You can try pushing the mode selector lever down once to change from AUTO LVL to AUTO, changing the timebase and working all the pushbutton switches a few times to see if anything changes. It probably won't and it looks like there's an issue near the U700 A-Sweep hybrid or its related circuitry. If the cursors and readouts are working, U800 and a lot of other things are working fine. Hopefully you have another scope to use in troubleshooting?
Whoops lol, didn’t realize they were upside down. Unfortunately it’s my only scope, so may need to figure something else out. Will at least pop it open and see if there is anything obvious and check some voltages
U700 and U900 are the same hybrid, the are used for the sweep circuits. 155-0240-00 or 155-0240-01
You can try to swap them. See if that works.
They almost never fail is my experience, but you never know, it's easy test.
And for sure check the power supply voltages.
I tried to see if I could get the B-sweep to work, but no luck (but again not sure if that was user error), will try swapping hybrids and see if that helps
If it's never had a PSU service, check the condition of the capacitors, they leak conductive electrolyte and short circuits of the PSU circuitry can cause damage, to lots of parts all over the scope, the caps in the picture are from a 2465 of similar age to your scope.
Does connecting a signal to the inputs change the trace at all?
David
I swapped the hybrids with no change. Power supply voltages test good. I went through the horizontal troubleshooting tips and 1,2,4 and 5 seem to check out (how long should the voltage ramp on pin 18 take? as it takes a few minutes to ramp up and down). Couldn't check step 3. Pin 11 on U800 is showing -5.6V As per the manual I checked voltages on U800. I'll start working through troubleshooting procedure 5 as best I can without a second scope. One thing I noticed, should the TRIG'D LED stay illuminated? I get get it to flash momentarily when switching modes
The caps on the A1 board look good, power supply voltages test good, but I'll open it up to check their condition, I don;t believe it's been re-capped, but it was well maintained before I got it. I can get vertical deflection as expected when I hook the probe up to a known DC voltage. Just no sweeps
One thing I noticed, should the TRIG'D LED stay illuminated? I get get it to flash momentarily when switching modes
If you connect CH1 to the calibrator output and select a reasonable vertical setting, then you should be able to get the trigger light to blink or stay illuminated in the NORMAL mode. You should also see your dot become a vertical line.
Not sure exactly what changed (reseating U700?) but my sweep is back
Not sure exactly what changed (reseating U700?) but my sweep is back
With a portion of intensified trace from the dual timebase.
And it's gone again
Not sure where to go next, might need to see if I can borrow another scope to troubleshoot it further
On your probing of pin 18, the ramp will take as long as the sweep, approx. 10x the sweep setting to cover all 10 divisions. If you're measuring with a voltmeter with the prescribed test settings, you'll never see the ramp because it's too fast. One thing you could do is turn the sweep down to 0.5s/div. The sweep across the screen will take about 5 seconds, and you should be able to see such a slowly changing ramp on a voltmeter.
Since you're getting a vertical deflection, you could also probe pin 18 with Ch 1, again at a slow sweep. With this problem on your scope, what you should see is a dot slowly going up and then resetting, repeatedly.
What are you seeing on the back panel A GATE OUT? A logic high here indicates that the A sweep has been triggered.
Does XY mode work? Seems that it probably should given the other symptoms.
I would also try removing and gently cleaning the contacts with isopropyl on hybrids U500 (trigger) and U650 (display sequencer). Don't mess with the nut on U800; it is prone to failure from mechanical stress.
I’ll take another look, been out of town recently. XY mode seems to work, and I’ll check the voltage on pin 18 to see what I see.
Brilliant idea using the scope itself on pin 18 (scope, heal thyself). I’m not seeing any change in voltage on pin 18 (I checked at variety of timing settings). Not seeing any change on pin 9 of U735 either, which should be the A sweep from U-700. I get a near constant -1.24 volts here. Tried swapping U700 and U900 again but no change
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I’m not seeing any change in voltage on pin 18 (I checked at variety of timing settings). Not seeing any change on pin 9 of U735 either, which should be the A sweep from U-700. I get a near constant -1.24 volts here. Tried swapping U700 and U900 again but no change
Swapping U700 and U900? I had suggested cleaning the contacts on U500 (trigger) and U650 (display sequencer). I'm suggesting this because the sweep came back by itself with no explanation, and both of those hybrids are involved in controlling the A sweep hybrid U700.
It's good to know pin 9 of U735 is not doing anything either, since that's coming right out of the A sweep hybrid.
I also asked what A GATE OUT is doing to know if the A sweep is triggering. Perhaps just the sweep output on U700 is broken. And also if XY mode is working normally. XY mode suspends both sweeps, so it is worthwhile to make sure its ok (although it doesn't say if it might be stuck in XY mode).