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Tek 465B blurred channel 1 trace

Timothy
 
Edited

I really love old electronics so I bought a non functioning 465B that appears as new. I would like a little help isolating its problems. I am a hobbyist so my skills are limited but I am eager to learn.

https://groups.io/g/TekScopes/photo/56677/2?p=Name,,,20,1,0,0

When I received the item is was purchased as NO TRACE from a guy who used to repair test equipment (diagnosed in 1984 as having a short jittery sweep, all modes, sweep displayed with only 1/8 proper deflection; X gain has an overage in gain that is nonadjustable. But then in 1992 it was crossed out and had "NO TRACE" written over it.) It has sat in a covered parking area since at least Feb 1992. I still paid well, despite it being covered in 26 years of dirt, due to the condition of the front face. In fact when I began trouble shooting there was no trace, not even with the beam finder. I did put it in XY mode and was able to see a faint dot. This allowed me to rule out the CRT.

I turned it on and off a dozen times when checking and probing and one time I turned it on and both traces returned. I don't know why.

There are a few problems still. The most obvious one I want to address first is a blurred trace when running full bandwidth on channel 1. The problem seems to go away when I limit the bandwidth to 20mhz. I hope once this is repaired other issues will be resolved as well.

https://groups.io/g/TekScopes/photo/56677/10?p=Name,,,20,1,0,0 limited BW
https://groups.io/g/TekScopes/photo/56677/11?p=Name,,,20,1,0,0 unlimited BW

The voltages appear to be in spec with ripple also within spec. I have checked for open tantalum caps by probing each for resistance and found none. That is about the limit of what I have done aside from reading every thread I could find on 456B issues.

I did find some spots on the board that appeared soiled. I am not sure if it is related, I don't see any caps near, perhaps its caused by a bad transistor or diode?

https://groups.io/g/TekScopes/photo/56677/0?p=Name,,,20,1,0,0
https://groups.io/g/TekScopes/photo/56677/1?p=Name,,,20,1,0,0

The beam finder now works but not when fully depressed. Upon close inspection it appears to be damaged.

https://groups.io/g/TekScopes/photo/56677/9?p=Name,,,20,1,0,0

More pictures of the boards

https://groups.io/g/TekScopes/photo/56677/5?p=Name,,,20,1,0,0
https://groups.io/g/TekScopes/photo/56677/6?p=Name,,,20,1,0,0
https://groups.io/g/TekScopes/photo/56677/7?p=Name,,,20,1,0,0
https://groups.io/g/TekScopes/photo/56677/8?p=Name,,,20,1,0,0

Thank you
Timothy

Timothy
 
Edited

Spec | Actual | Ripple peak to peak | Ripple peak to peak
. | | Oscope | multi meter

+110 | +112.0 | 43mv | 5.8mv
+5 | +5.0 | 14mv | .40mv
+55 | +55.0 | 13mv | .38mv
+15 | +15.0 | 15mv | .36mv
-8 | -7.9 | 15mv | .37mv

The ripple is high on all test points according to the manual when measured with my Oscope. These were taken with my Oscope and the spring ground. I get lower readings when I use my multi meter. I must be doing something wrong?

And the traces have both disappeared again.

 

Your multimeter reads peak to peak? That's pretty unusual. Most read RMS or Average.

----- Original Message -----
From: "Timothy via Groups.Io" <mustang_gt_y2k=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Saturday, June 09, 2018 2:55 PM
Subject: Re: [TekScopes] Tek 465B blurred channel 1 trace


[Edited Message Follows]

Spec | Actual | Ripple peak to peak | Ripple peak to peak
. | | Oscope | multi meter

+110 | +112.0 | 43mv | 5.8mv
+5 | +5.0 | 14mv | .40mv
+55 | +55.0 | 13mv | .38mv
+15 | +15.0 | 15mv | .36mv
-8 | -7.9 | 15mv | .37mv

The ripple is high on all test points according to the manual when measured with my Oscope. These were taken with my Oscope and the spring ground. I get lower readings when I use my multi meter. I must be doing something wrong?

Timothy
 

My mistake, it should say RMS, I cut and pasted

 

A muti-meter reads in RMS volts, which will always be lower than a scope measurement, which is Peak-Peak.
However, if you rotate the Vert Variable knob fully CCW, it will give a close approximation to RMS.On most scopes, the Variable range is "at least 2.5:1".
This is close to 2.7 to 1, which is the conversion factor from P-P to RMS (sine)

Timothy
 
Edited

Even with as out of spec as the PSU is I have been getting intermittent traces on the screen and one of the two traces was pretty clean. The last time I turned it on I heard a pop and shut it off quickly. When I turned it back on the traces had returned but things were different. There was a significant amount of noise/distortion on both traces. Trace 1 was blurry but not as blurry as before and trace 2 now shows equal blur. Then the traces faded again. I could not locate and visibly damage components on the external boards. Prior to this I did swap out the .0047 6kv paper cap with one from a 468B because I thought it was reading bad out of circuit. Im not sure if its related since newer part was identical.

I am going to get a second 465B that I can use to compare readings on components with to help me isolate the issues. This way I dont have to pull parts off of boards to test as much.

It seems there are at least two faults I need to deal with. And eventually I believe I will have to recap the PSU and maybe more.

Timothy
 

For my fading problem I think I have narrowed things down to electrolytic (or is it wet tantalum?) caps, C4327 5uF 150V, and C4006 4.7uF 35v (leaked some). C4327 was arcing sometimes when powering on! These seem like bipolar caps, correct? What are suitable replacements? I see someone recommending electrolytic polar caps, is that right?

Ive placed an order with JLCPCB for adapter PCBs and will be recapping the filtering caps on the PSU soon. Once that is done I will get to work on cleaning up the traces.

Timothy
 

I am posting an update as I am back on to trying to fix my 465B.
I thought a working scope would help me troubleshoot a intermittent problem but I ended up not needing one.

I changed out the smoothing caps and all my voltages are now within spec and ripple is hard to detect.

Since my problem was intermittent I may have let myself be lead down the wrong path, very embarrassing. I had no trace, I pulled the W4032 jumper (HV Mult GND) and my trace came back. This lead me to believe the HV multiplier was bad. I swapped it out and my trace came back. I turned off the scope because I forgot to put the cover back on the hv multiplier and needed to remove the vert preamp board to do so. Once I got it all back together I had no trace and no -8v. Every time I had measured previously I had -8v but I am worried I changed out the HV multiplier without needing to do so.

Moving forward and using isolation, I determined the vertical output board was the culprit. I couldn't find any bad components so I re-seated all the transistors and the CRT vertical deflection driver and Voila! I had my traces back and cleaner than ever. I still have a problem with distorted square waves but fuzziness is gone.

I need to test my old HV multiplier to see if it is good or bad. Maybe I just bumped something on the Vert Ouput board when I was removing the CRT. Or perhaps this was the problem all along.

I need to figure out why square waves are so bad on both channels. it looks like excessive ringing.