Tektronix 2465 CRT Issue - Page 1
Forum section: electronics / repair

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 12, 2023, 01:15:32 am
content: Not new to repairing electronics, but a total newb to working on scopes. This 2465 (non A or B, but has the DMM option) powers up, but I get nothing but a faint glow on the screen. That glow does somewhat respond to the Intensity pot. Pressing Beam Find does nothing. So far the only troubleshooting I've done is to check the low-voltage power supplies against the chart in the service manual--they're all within spec, though I haven't measured ripple yet. Obviously I'm not going to probe around the HV section without an appropriate probe (don't have one) and some direction from you folks. I'm attaching a photo of the current panel settings on the off chance I've missed something stupid, but I fear it's more serious.[ Specified attachment is not available ]

author: jonpaul
author_rank: Super Contributor
timestamp: April 12, 2023, 01:48:42 am
content: bonjour cher Monsieur2336 is NOT 2465, and a blank screen is NOT normally a CRT issue.1. get service manual for the serial number range see Tekwiki and w140.2. Follow troubleshooting flowcharts3. most of these decade's old scopes are still fine, most likelya. use control,cleaner on all pots, contact cleaner on all switches except V/ div verticalExercise every control.b. if no traces in TRIG AUTO, or BEAM FIND, suspect HV transformer and multipliersc. HV test points are on HV shield area, and at cathode V, perhaps 1500...2200V.Easy to check with a VOM and HV probe.d. If the V or H out amps are bad the traces are deflected off screen, but visible in BEAM FINDbon chanceJon

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 12, 2023, 02:06:09 am
content: Thanks Jon. I attached the wrong pic, obviously. The correct one is now in my first post.I do have the 2465 service manual. I'll check the troubleshooting flowcharts, clean the pots, and, if necessary, turn my attention to the HV transformer and multipliers.

author: jonpaul
author_rank: Super Contributor
timestamp: April 12, 2023, 03:41:45 am
content: hello againthis is a very abused, early SN model with the dreaded DVM option, much more difficult to service.There is an options service manual for DVM option.The beam finder push-button is a suspect, needs cleaning and testing.The caps in PSU, RIFA VDE X,Y blow up over the years and PSU electrolytics go bad.Check in "tektronix 2465 teardown" thread 72 pages! on eevblog.Also Tekscopes2 and tekscopes on groups.io. Suggest you post your results and questions on all three forums, as lots of tektronix ex techs and engineers on tekscopes forums.JonPS History..first scope...Tektronix 1968, 545, a 453 in 11970s, then 465 and 1990 2465...Photosmy 2465/7/B bench.....

author: Nikola Tesla Junior IV
author_rank: Contributor
timestamp: April 13, 2023, 06:37:18 pm
content: Nice Printer!You may know this- quick way to see if there is a beam displayed anywhere. I have seen scopes so far out of calibration the beam would barely show at max positioning.-Turn on all 4 channels and punch that beam find button several times, as pointed out above, if you see a flicker, this button could be the culprit.-adjust trace intensity to high momentarily - I have seen this calibrated to barely visible.-set SEC/DIV to .1-make sure X10 Mag is off-turn Vertical position knobs back and forth, and hit that beam find button a couple more times.If you don't see something, then above post byJonpaulis where I would begin, good info.

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 14, 2023, 12:34:11 pm
content: Tried those suggestions, but no success. I'll start reading that 2465 teardown thread. . . .

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: April 14, 2023, 01:17:09 pm
content: Perhaps check if the tube filaments light up.If they do not clean the tube socket and check the tube pins for filament continuitySometimes the connection in the tube base becomes corroded and needs resoldering.

author: bdunham7
author_rank: Super Contributor
timestamp: April 14, 2023, 01:29:33 pm
content: Turn the timebase knob all the way back to 'XY'. Make sure the CH1 and CH2 buttons are in, all other mode button out. Select 'GND' (either one) for both CH1 and CH2. Turn the intensity all the way up and then use the position knobs at the top of the panel to try and get a dot on the screen. If you can't, you'll need to take the scope cover off and have a look. Make sure you have a fan that can be set up to blow air on the bottom of the main circuit board any time you power the scope on with its case removed. Is the scope's built-in fan original and does it work?

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 14, 2023, 09:16:18 pm
content: No luck. When I push the beam finder some large areas of the screen glow brighter. Same when I turn the position knobs. But no trace, and no dot.It appears to be the original fan, and it works.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: April 14, 2023, 10:10:51 pm
content: HiSounds like you have a problem with the CRT focus voltage.G Edmonds

author: bdunham7
author_rank: Super Contributor
timestamp: April 14, 2023, 11:41:10 pm
content: If you are certain that you've verified that the +87V power supply rail is good, take a measurement at point 69 on the HV circuit board (with great care of course, there's high voltage on the board). As mentioned, a complete failure of the focus system may cause your problem.

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 15, 2023, 12:13:36 am
content: Quote from: bdunham7 on April 14, 2023, 01:29:33 pmGonna double down on this. OP: Heed this advice! Those heatsinked ICs are hard to get, custom Techtronic's parts, which can overheat and be damaged if just cooled by convection.

author: jonpaul
author_rank: Super Contributor
timestamp: April 15, 2023, 12:27:34 am
content: 1/ Find an test focus and inten and astig pots2/ Many high R resistors in HV section can go high in vlaue over the decades3/ Never fool with the thick fim hybridgs eg the HOR IC if they are not suspected.Bon chanceJon

author: Nikola Tesla Junior IV
author_rank: Contributor
timestamp: April 15, 2023, 04:49:33 am
content: Quote from: jonpaul on April 15, 2023, 12:27:34 amThis again, is great advice, with emphasis on the ASTIG pot. It's a good a place to start and can be a good end if the High R resistors mentioned above have drifted only moderately, and can be cured by adjustment. Start easy first.

author: dietert1
author_rank: Super Contributor
timestamp: April 15, 2023, 06:57:18 am
content: In the 2465 the horizontal deflection amplifier is known to fail. Reason being a strange thermal mount that can disrupt bond wires inside. Result would be no display (beam outside of screen).On ours i had to fix this once. As far as i remember i got a replacement from ebay/china. Of course i modified the mount to reduce the risc. It has been working ever since.Regards, Dieter

author: factory
author_rank: Super Contributor
timestamp: April 15, 2023, 12:09:25 pm
content: Does the readout intensity control have any effect? Note: the readout intensity & the intensity controls are part of the inputs to U650 on the mainboard, not the HV board.U950 on the mainboard has bright & blank inputs from U650 & high drive focus from the HV board.Focus & Astig controls go to the HV board.A faulty PSU can take out various parts in these scopes too, someone I know on another forum had multiple failures of parts caused by the PSU, the scope had been sold as recapped, sadly they only recapped the RIFAs. Damage was caused to the HV board, a couple of ICs for the controls on the A5 board, two CA3046 transistor arrays near U400 and the U950 hybrid on the mainboard, probably a few more that I can't remember now.David

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 17, 2023, 10:36:40 pm
content: Quote from: bdunham7 on April 14, 2023, 11:41:10 pmI had a chance today to measure the voltage at point 69. I'm getting 22.40V.Fan blowing on the bottom the entire time.

author: james_s
author_rank: Super Contributor
timestamp: April 17, 2023, 11:15:33 pm
content: From the description of the symptom, I suspect the beam is off the edge of the screen and impacting the side of the tube with some stray electrons causing the glow. I would try measuring the voltage on the deflection pins to confirm this.

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 19, 2023, 02:39:56 am
content: Thanks for the direction james_s.

author: bdunham7
author_rank: Super Contributor
timestamp: April 19, 2023, 03:46:39 am
content: Quote from: TimeBandit on April 17, 2023, 10:36:40 pmOK, I don't see a specific issue with that (it's not pegged at +87 and it isn't zero) so I'd move on to the horizontal deflection system. Does the vertical position knob on the active channel make any difference to the pattern of glow on the screen? Try this in a darkened room.

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 21, 2023, 08:46:52 pm
content: Quote from: bdunham7 on April 19, 2023, 03:46:39 amYes, it does. Turning the vertical position knob all the way to the left makes the glow completely disappear, and turning it all the way to the right reduces it by about 80 percent.

author: jonpaul
author_rank: Super Contributor
timestamp: April 22, 2023, 03:33:14 am
content: Rebonjour:Suggest you follow the horamp trouble flow char.Place in XY modeset inputs to GRDuse another scope or DVM, follow H amo starting at CRT H defl plates, back.You should se equal L and R plate and other amp signals as the path is differential.IF the plates have very unequal voltage, use HOR POS see how they varty.Should be possble to have equal plate V.If not you have a clewJon

author: George Edmonds
author_rank: Frequent Contributor
timestamp: April 22, 2023, 06:00:09 am
content: HiA simple way of determining if it is the deflection amps or the CRT voltages is to put a hand held (not a bench one ) between the horizontal deflection plates (TP W818 and W819) and press the beam finder, you should see a low voltage. Then do the same with the Vertical deflection plates (W916 and W917 again you should see a low voltage with the beam finder pressed.In XY mode you should be able to achieve zero volts using the vertical and horizontal shifts.Please be aware that this scope has dynamic focus and other dynamic “features” that will make it difficult to fault find.G Edmonds

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 24, 2023, 11:14:21 pm
content: Ok, update:Measuring across the horizontal deflection plates (W918 and W919) I saw voltage fluctuating from 70V to 74V, dropping to between 40V and 43V when the beam finder was pressed.Measuring across the vertical deflection plates (W916 and W917), I saw voltage fluctuating from 3V to 10V, dropping to between 1V and 4V when the beam finder was pressed.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: April 25, 2023, 03:12:21 am
content: Hi TimeBanditFrom the information you posted it is not a CRT problem, The failure is almost certainly in the horizontal output amplifier U800, a Tektronix dedicated IC.There is a known high failure rate with them, especially if the fan has failed or the scope is run without its case in place. If you need to run the scope without the case you MUST provide additional cooling.I suggest that you Google “Tektronix U800”,The Tektronix part number for U800 is 155-0241-01 or 155-0241-02G Edmonds

author: dietert1
author_rank: Super Contributor
timestamp: April 25, 2023, 07:49:32 am
content: Here i have an image of the U800 repair i mentioned ten days ago. I mounted the replacement stress-free and added a small heatsink to compensate for a possible loss of heat conduction.Regards, Dieter

author: Nikola Tesla Junior IV
author_rank: Contributor
timestamp: April 25, 2023, 09:37:38 am
content: I may be incorrect, it's late here;It is my opinion that your readings from those locations (U600 Vertical Output, U800 Horizontal Output) should be verified in depth. I have included some images for you to use as a guide.Other things that may apply: GAIN R860/R850; ASTIG R977; HDC R3401 / R3407; HRZ R801 ------ 3100;809;804; Q1851.Q1852, R615 & others.

author: TimeBandit
author_rank: Regular Contributor
timestamp: April 28, 2023, 07:05:43 pm
content: Okay, I checked for the waveforms as indicated. Here's what I found.#56, #57: Very distorted square waves.#58: Nothing.#59: Significantly different waveform.#60, #61: Ok, matches the waveforms shown.#62: Significantly different waveform.#63: Nothing.

author: MathWizard
author_rank: Super Contributor
timestamp: May 01, 2023, 10:15:27 pm
content: So iirc, the 2465 has a reputation as 1 of the best CRT analog scopes. It has a lot of IC's and stuff ?What were the best scopes, that were all discrete BJT's/FET's, and maybe a few op-amps ?? When would that have been , the 1950's or 1960's ?

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2023, 08:37:12 pm
content: Tek 465 has no custom ICs as far as I know. The 22xx series from the 80s also didn't have these custom ICs. Back in the 50s and 60s scopes were made with vacuum tubes, there were loads of discrete solid state models in the 70s and 80s.

author: Kwakerman
author_rank: Regular Contributor
timestamp: May 07, 2023, 09:48:42 pm
content: I'd suspect U800 as I had one with similar issue. Disconnect the deflection plate wires from the tube (the ones going through the PCB hole near U800). When you switch on you should get a series of vertical spots, one near the top of the screen for the cursor display, 1/2/3 or 4 dots depending on how many channels you have selected that will move up and down with the vertical position controls and another set at the bottom for timebase & gain readouts. If you can see that and the blobs react to focus / intensity / trace position then you know the basics are working and the horizontal deflection (U800) area has a fault. On my one, one of the U800 outputs for the deflection plates was open circuit so the other output was pulling the beam way off to one side.

author: TimeBandit
author_rank: Regular Contributor
timestamp: May 10, 2023, 01:24:34 pm
content: Quote from: Kwakerman on May 07, 2023, 09:48:42 pmI did as you suggested and the blobs appeared and reacted pretty much as you described. I'll look into replacing the U800.

author: Kwakerman
author_rank: Regular Contributor
timestamp: May 12, 2023, 09:00:24 am
content: This 154246923795/ebay] may be an option, I used one of the original V1 versions in one of my scopes and it works fine for what I needed that scope to do (general work). I have another couple of scopes with the correct U800 if I need to do super accurate work. No experience of the V2 but hopefully it can only be an improvement to the V1 that I am happy with.