Tek 2465 Horizontal Sweep Issue - Page 1
Forum section: electronics / testgear

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 01:17:51 am
content: 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 scanThanks

author: tautech
author_rank: Super Contributor
timestamp: April 19, 2024, 01:23:41 am
content: Welcome to the forum.Check it is not set to XY mode.

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 01:43:06 am
content: I don't think so. I've got the Sec/Div switch set to 100ms locked

author: bdunham7
author_rank: Super Contributor
timestamp: April 19, 2024, 01:43:38 am
content: Quote from: kellymcdonald78 on April 19, 2024, 01:17:51 amCan 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.

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 01:50:14 am
content: Here you go. I also ran the self test and it comes back clean

author: bdunham7
author_rank: Super Contributor
timestamp: April 19, 2024, 02:24:28 am
content: 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?

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 01:55:51 pm
content: 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

author: Orange
author_rank: Frequent Contributor
timestamp: April 19, 2024, 03:03:07 pm
content: U700 and U900 are the same hybrid, the are used for the sweep circuits. 155-0240-00 or 155-0240-01You 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.

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 05:00:04 pm
content: 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

author: Orange
author_rank: Frequent Contributor
timestamp: April 19, 2024, 05:28:09 pm
content: There is a good service manual available herehttps://w140.com/tekwiki/images/8/8b/070-3831-00.pdfIt has a flow chart for diagnosing the sweep circuit on page 283

author: factory
author_rank: Super Contributor
timestamp: April 19, 2024, 05:55:58 pm
content: 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

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 08:09:47 pm
content: 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

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 08:13:15 pm
content: 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

author: bdunham7
author_rank: Super Contributor
timestamp: April 19, 2024, 09:45:34 pm
content: Quote from: kellymcdonald78 on April 19, 2024, 08:09:47 pmIf 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.

author: kellymcdonald78
author_rank: Contributor
timestamp: April 19, 2024, 10:54:59 pm
content: Not sure exactly what changed (reseating U700?) but my sweep is back

author: tautech
author_rank: Super Contributor
timestamp: April 19, 2024, 11:07:01 pm
content: Quote from: kellymcdonald78 on April 19, 2024, 10:54:59 pmWith a portion of intensified trace from the dual timebase.

author: kellymcdonald78
author_rank: Contributor
timestamp: April 27, 2024, 02:24:35 am
content: And it's gone againNot sure where to go next, might need to see if I can borrow another scope to troubleshoot it further

author: MarkL
author_rank: Unknown
timestamp: April 27, 2024, 02:13:25 pm
content: 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.

author: kellymcdonald78
author_rank: Contributor
timestamp: May 08, 2024, 03:41:49 am
content: 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.

author: kellymcdonald78
author_rank: Contributor
timestamp: May 09, 2024, 01:49:03 am
content: 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

author: MarkL
author_rank: Unknown
timestamp: May 14, 2024, 02:20:17 pm
content: Quote from: kellymcdonald78 on May 09, 2024, 01:49:03 amSwapping 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).

author: kellymcdonald78
author_rank: Contributor
timestamp: May 18, 2024, 06:53:05 pm
content: I’ve cleaned contacts on U700, U900, U600 and U500. U650 is a 40 pin DIP on my unit.Looking at XY mode, I get a diagonal deflection when I attach channel 1 to the calibration pin (pic attached). I can see on the display it switching out of XY mode when I switch the sec/div selector (I do notice a little bit of horizontal drift when I switch to very short divs (like 100 ns)A Gate appears to be showing about 4.5V (constant as far as I can tell)