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Troubleshoot TEK 465


wes Bolin
 

I am trying to repair a TEK 465 oscilloscope that my friend bought from ebay. It does not have a trace unless I push the Beam Finder button. A trace then appears that I can move vertically, horizontally, focus and vary intensity. I do have the sawtooth output from the Horizontal Amp that varies with the front panel switch position. Where
do you suggest I look next?

I do have some test equipment to be used for troubleshooting. I'm used to using scopes, not repairing them, so any help is sure appreciated. Thanks.
Wes
Texarkana, AR


Bob Albert
 

Seems like an unblanking issue.  Trace the signal that is supposed to raise the CRT control grid potential during sweep.  Sweep gate.

On Tuesday, January 5, 2021, 03:24:13 PM PST, wes Bolin <k5apl41@gmail.com> wrote:

I am trying to repair a TEK 465 oscilloscope that my friend bought from ebay.  It does not have a trace unless I push the Beam Finder button.  A trace then appears that I can move vertically, horizontally, focus and vary intensity.  I do have the sawtooth output from the Horizontal Amp that varies with the front panel switch position.  Where
do you suggest I look next?

I do have some test equipment to be used for troubleshooting.  I'm used to using scopes, not repairing them, so any help is sure appreciated.  Thanks.
Wes
Texarkana,  AR


Mlynch001
 

Wes,

What kind of signal are you applying to the input(s)?. How is your front panel set up? It could be a simple case of the front panel being set wrong.

--
Michael Lynch
Dardanelle, AR


wes Bolin
 

Thanks Dave & Michael for ideas and suggestions.. I did set the front panel up as you suggested. No Line Low light. TP1486 has good signal. More info:
I push Beam Finder all the way in and no display. Pushing about 1/2 way in I get a trace that I can vary intensity, focus, Vert and Horiz position.

There is no Light on CH2 amplitude indicator knob. All P.S. Voltages check OK. Have Calibrator output I can see on another scope. I do have ramp voltages at Sweep A and B going to CRT.

Any more help will be appreciated.
Wes


Bob Albert
 

If you have signals to the CRT you may not have high voltage or heater supply.  Since you do get some traces that points to intensity signals, the grid signal to the CRT.
Bob

On Thursday, January 7, 2021, 01:34:14 PM PST, wes Bolin <k5apl41@gmail.com> wrote:

Thanks Dave & Michael for ideas and suggestions..  I did set the front panel up as you suggested. No Line Low light.  TP1486 has good signal.  More info:
I push Beam Finder all the way in and no display.  Pushing about 1/2 way in I get a trace that I can vary intensity, focus, Vert and Horiz position.

There is no Light on CH2 amplitude indicator knob.  All P.S. Voltages check OK.  Have Calibrator output I can see on another scope.  I do have ramp voltages at Sweep A and B going to CRT.

Any more help will be appreciated.
Wes


Michael W. Lynch
 

Wes,

Many scopes have very dirty or corroded beam finder switches. Clean and exercise all switches, these are major troublemakers.

Does the scope show to trigger on the calibrator signal?

Do you have an "A Gate" signal at the top rear panel BNC? When attached to your test scope, you should find a pulsed square wave with the scope running in the AUTO Trigger mode and "Normal" Trigger source. Do you see this?

Input the calibrator signal to CH1 BNC, Set scope to 50mV, 1 ms Time/Div. Should have a 6 vert division square wave with about 10 cycles horizontally. You should get a very similar signal on a scope connected to the 3rd BNC from the top of the rear panel and the scope adjusted to the same settings. Do you see this?

This tests the Vertical pre-amp and CH1 attenuators. No signal, then the vertical pre-amp has a problem.

If you have the correct equipment, you might want to check the -2450 Cathode voltage. There is a hole in the HV shield attached to that bottom board.

Since You have a display when using the beam finder, that would indicate that the HV section is not totally "out to lunch".

--
Michael Lynch
Dardanelle, AR


Dave Peterson
 

Wes,

If you have access to the service manual, go through the "Power Supply" and "Display and Z Axis" portion of the calibration procedures.

In the B250000 and up service manual:
https://w140.com/tekwiki/images/5/55/070-1861-00.pdf

There's a "No Visible Display Troubleshooting" guide on page 214/251 when viewing pdf in Chrome. It's after the schematics.

Dave


Dave Peterson
 

Oh, and the channel indicator bulbs are also a frequent failure. Both my 465 have one of the two channels 1x bulbs out. I suspect the 10x bulbs are less frequently out as they probably don't get as much activity.

You can test the 10x bulb by grounding the ring at the base of the CH1/CH2 BNCs on the face.

You have to remove the vertical assembly to get at the bulb assemblies. Leave it until you are ready to tackle that.

Dave

P.S. Anyone have a reference to a source of these bulbs? I'll be needing to buy some.


Michael W. Lynch
 

Dave,

I hate those bulbs and what you have to do to replace them. That was a major upgrade for the 465B, they got rid of the incandescent bulbs and went LED. I have two scopes right now that have blown lamps, I dread changing them.

--
Michael Lynch
Dardanelle, AR


Tom Lee
 

Nearly every 465 that I own has one or more dead bulbs, and I'm leaving them that way. They're just too much of a PITA to fix. Maybe after retirement...

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 1/7/2021 16:54, Michael W. Lynch via groups.io wrote:
Dave,

I hate those bulbs and what you have to do to replace them. That was a major upgrade for the 465B, they got rid of the incandescent bulbs and went LED. I have two scopes right now that have blown lamps, I dread changing them.


John Williams
 

Michael. I agree to some extent about changing these bulbs. I have replaced a few and didn’t find it too bad. Here’s what I did. It is easiest to remove the front panel. It comes off once the knobs and nuts holding the controls are removed. The only tricky part was removing the time/cm knob which requires a bit of care and a long Allen wrench. Once the panel is off it is easy to remove the bulb holders and resolder new bulbs in place. I have a few of the units from eBay purchases as spares.


Mlynch001
 

John,
Thanks for that information! I’ll try that next time. I usually replace them when I have the Vertical section out, but I don’t want to pull out just to replace the lamps.

--
Michael Lynch
Dardanelle, AR


quad@...
 

If you ever decide to change the lamps to LEDs, here is an informative thread -

https://www.antiqueradios.com/forums/viewtopic.php?p=906063