Tektronix 465B Questions and Problems

[nick39]

Hi,

I recently purchased a Tektronix 465B. The scope did not power on because it had 2 shorted 6.8uF tantalun capacitors C1464 and C1468. Replaced them with 2 3.3uF electrolitics in parallel because I dont have tantalun right now (I see if I can get them later) but as far as I see in the schematic they dont seem to be critical. They just seem to be decoupling. Now here are the first things I noticed:

1- With the metal cover removed. I noticed there is a lot of 50Hz line noise on both channels trace. The noise gets worse if I move my hand close to those two caps I replaced or if its close to the attenuator blocks. They have the following numbers (PN200-1439-00). The noise goes away completly if I touch the metal case and put my hand very close to those two caps.

2- If I turn off both CH1 and CH2 (both switches are depressed at the same time) the noise goes away but the trace is not vertically centered on the screen. Its 1.2 divisions up. Is this a normal behaviour for this scope?

3- Both channels dont seem to be centered because if I put the position know in the middle the trace is off for almost 1 div.

4- The Volts/Div scale on CH2 is not working properly. Scales .1 and .2 are completly off and they are very noise when I touch the know or the "AC GND DC" switch.

5- How does the "BLY'D SWP PULL" know work? I cant adjust the allen screws because if I do it appears to block the know. I have to leave both screws unscrew which makes pulling from that know useless.

Another thing I noticed is that it has a sticker on the back that reads: "Digital Equipment Corporation CAPITAL ASSET" any idea what this means?

I'll appreciate any help because this is my first Tek scope and I would very much like to have it working properly.

[factory]

Another thing I noticed is that it has a sticker on the back that reads: "Digital Equipment Corporation CAPITAL ASSET" any idea what this means?

Just part of it's history, once owned by Digital Equipment Corporation aka "digital" or "DEC", a computer maker that got eventually got taken over by Compaq, which then got taken over by HP.

David

[tggzzz]

Have you downloaded the 465B service manual? (The 465 is significantly different)

1: probably normal

 2,3: insufficient information

4: Volts/div scales.

Quite possibly dirty switch contacts. To clean them, first switch them many times to see if that moves dirt.

The Tek gold finger contacts are fragile if abused. When switching them fails, take a strip of smooth paper, put IPA on it, open contacts, put wet paper between contacts, close contacts, pull paper away from the contacts being careful not to bend the fingers.

5: not sure what you mean.

[nick39]

I think I just fixed the 50Hz noise issue. Someone changed the mains and did not connect the ground wire (the green and yellow). So I just reconnected it and it fixed that noise issue.
What I was trying to explain in 2 is that the scope has 2 switches on the left side next to the screen that say "CH1" and "CH2" if you depressed both of them it seems to turn both channels off because the LED indicator of the scale goes off. In this mode the trace does not go to the center of the screen. Instead it moves upwards 1.2 division. I'm not sure if this is normal behaviour.
And in 3 the issue seems to be the position knobs were not centered. As for the "TIME/DIV and DELAY TIME" knob. I'm going to see if I can find more information about how this works because I dont think I'm setting it right. Finally for the CH2 issue I'll try to clean those contact.
Thanks!

[Wallace Gasiewicz]

As I recall the two channel sweeps are not meant to be centered at the same vertical, so you can tell them apart.  Since they are the same color. This is adjustable.

"BLY'D SWP PULL"  Is DELAYED SWEEP -------" PULL"  the knob to add a delayed sweep.  Read about this in the manual. 

Advice on cleaning the contacts is good, the paper of choice used to be a dollar bill, since this is really more like cloth and less abrasive than paper. also does not fall apart with solvent. 
As tgzzz sez: be very careful with the spring contacts on the switches.

About 50-60 Hz noise, short the inputs to their respective grounds or short the probe leads to their ground leads and see if this goes away. 

The higher resolution scales are hard to adjust well and get noisy when switches are dirty, again try the probe to ground connection to see if they get better.   

Congratulations on your small boat anchor,  ----  it cost as much as a car when new.   

If ordering probes, make sure that they are the correct capacitance and I personally would try to get 200 MHz probes rather than just 100 MHz.

[tggzzz]

I think I just fixed the 50Hz noise issue. Someone changed the mains and did not connect the ground wire (the green and yellow). So I just reconnected it and it fixed that noise issue.

You may also have saved your life. It sounds like the previous owner floated the scope.

For why that can be lethal and how to avoid that ignorant idiocy, see the safety refs at
https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

[nick39]

I found the issue of the noise and the scale problem. It wasnt the gold finger contacts because I cleaned them and it made no difference. It had broken solder joints inside the X10 and X100 attenuators on both CH1 and CH2! And for the TIME/DIV and DELAY TIME knob, I think I was tightening the the screws in the wrong position. What I did was to turn fully counterclockwise both the A TIME and then I pulled the shaft for the delay time and also rotated it fully counterclockwise. Now it seems to be turning correctly. I still have to learn how that delay time option work and test it but at least now I can start doing some tests.

[doktorabg]

Hi to all members!
I have a problem with Tektronix 465
I made a little repair but the problem exist
Before repair only -8V was bad , -0.12V after replace the CR1561 is -6.2V
On TP are +111.4V , +54.9V , +15V , +4.6V and -6.2V and now all three (newone) CR1561 , CR1551 , and CR1541 are hot
The resistans between -8V and GND is 55ohm
Look at the pictures and the bulb in Highvoltage section blinking!
Any help will be good!
Thank you!