Tektronix 2465 CRT Issue

[TimeBandit]

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 ]

[jonpaul]

bonjour cher Monsieur

2336 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 flowcharts

3. most of these decade's old scopes are still fine, most likely

a. use control,cleaner on all pots, contact cleaner on all switches except V/ div vertical

Exercise every control.

b. if no traces in TRIG AUTO, or BEAM FIND, suspect HV transformer and multipliers

c. 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 FIND

bon chance

Jon

[TimeBandit]

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.

[jonpaul]

hello again
this 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.

Jon

PS History..first scope...Tektronix 1968,  545, a 453 in 11970s,  then 465 and 1990 2465...
Photos
my 2465/7/B bench.....

[Nikola Tesla Junior IV]

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 by Jonpaul is where I would begin, good info.

[TimeBandit]

Tried those suggestions, but no success. I'll start reading that 2465 teardown thread. . . .

[Wallace Gasiewicz]

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.

[bdunham7]

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?

[TimeBandit]

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.

[George Edmonds]

Hi

Sounds like you have a problem with the CRT focus voltage.

G Edmonds

[bdunham7]

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.

[Kim Christensen]

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.

Gonna 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.

[jonpaul]

1/ Find an test focus and inten and astig pots

2/ Many high R resistors in HV section can go high in vlaue over the decades

3/ Never fool with the thick fim hybridgs eg the HOR IC if they are not suspected.

Bon chance


Jon

[Nikola Tesla Junior IV]

1/ Find an test focus and inten and astig pots

2/ Many high R resistors in HV section can go high in vlaue over the decades

3/ Never fool with the thick fim hybridgs eg the HOR IC if they are not suspected.

This 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.

[dietert1]

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

[factory]

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

[TimeBandit]

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.

I had a chance today to measure the voltage at point 69. I'm getting 22.40V.

Fan blowing on the bottom the entire time.

[james_s]

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.

[TimeBandit]

Thanks for the direction james_s.

[bdunham7]

I had a chance today to measure the voltage at point 69. I'm getting 22.40V.

Fan blowing on the bottom the entire time.

OK, 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.

[TimeBandit]

I had a chance today to measure the voltage at point 69. I'm getting 22.40V.

Fan blowing on the bottom the entire time.

OK, 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.

Yes, 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.

[jonpaul]

Rebonjour:

Suggest you follow the horamp trouble flow char.

Place in XY mode

set inputs to GRD

use 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 clew


Jon

[George Edmonds]

Hi

A 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

[TimeBandit]

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.

[George Edmonds]

Hi TimeBandit

From 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 155-0241-02

G Edmonds