tektronix 475 scope

[stusnyder]

Just picked this up from a friend who said he had no use for it anymore, he said he last used it 2 yrs ago. Got it home and tried it out...no display. Took the back off and noticed the crt gun had no glow to it, checked pins 1 and 14 and have no voltage, but the filament checks ok. It has 6 filter cans, single section. One got rather warm. Fuses are ok. Since this is 1971 vintage I'm guessing just replace all the cans???? Double sided circuit board, so lots of fun getting these cans out. If one or some of these cans were bad, would that interfere with the crt circuit?

[bob91343]

You need a manual. Find the source of power for the CRT heater and see why it's not getting to the tube socket. It may be a poor connector or broken circuit trace.

Yes, replace a warm capacitor but don't try to fix everything at once.

[Sandy G]

Bought a 465 for my company back in '81...It, & the cart was like $8-9K...IIRC, Tek offered authorised service/certified calibration til around 2000...But I can't remember oursever needing much of anything service-wise done to it. In fact, I think they STILL use it...Wait a minute, the guys gave me the CRT out of it in the '90s..I took it & executed it w/my trusty .22...But we'd replaced the CRT.

[jr_tech]

Originally Posted by stusnyder

Took the back off and noticed the crt gun had no glow to it, checked pins 1 and 14 and have no voltage, but the filament checks ok. It has 6 filter cans, single section. One got rather warm. Fuses are ok. Since this is 1971 vintage I'm guessing just replace all the cans???? Double sided circuit board, so lots of fun getting these cans out. If one or some of these cans were bad, would that interfere with the crt circuit?

I don't have specific knowledge of the 475, but many Tek scopes power the CRT heater from a winding on the HV supply transformer. Usually the lack of heater voltage implies that the HV supply is not working. It is also likely that you could have encountered a fairly high negative voltage at the heater pins had the HV supply been working. BE CAREFUL!! get a schematic and know what you are doing before poking around the CRT base in an oscilloscope.

jr

[stusnyder]

found lots of info on the yahoo tek group, seems like replacing all the cans are a good start. I got all 6 cans out, only one tests normal, the rest are poor.
Ordered replacements from digikey.

[N2IXK]

If you replace the twistlock cans with another style of caps, be aware that Tek used the multiple can connections to complete the ground circuit in several places. If you remove the old cans, you need to make sure that the ground lug pads are all tied back together as needed.

[stusnyder]

Originally Posted by N2IXK

If you replace the twistlock cans with another style of caps, be aware that Tek used the multiple can connections to complete the ground circuit in several places. If you remove the old cans, you need to make sure that the ground lug pads are all tied back together as needed.

Yea I already seen that. Anybody know where you adjust to 50v from?

[bob91343]

http://bama.edebris.com/manuals/tek/475

[stusnyder]

Ok replaced the filter caps tonight. Checked the voltages and they are right on the money. I can get a dot up on the screen via the beamfinder button, but no trace. Trigger is set on auto. Anybody have any ideas?

[old_tv_nut]

I think if the sweep was running, when you push beamfinder you would see an out of focus line instead of a dot.
So, maybe H sweep not working or just not being triggered?

[stusnyder]

Originally Posted by old_tv_nut

I think if the sweep was running, when you push beamfinder you would see an out of focus line instead of a dot.
So, maybe H sweep not working or just not being triggered?

I don't think its triggered. Supposedly if its in auto mode you should have a trace, normal mode won't show till it's triggered. Also the trigger light was not lit. Should I hook a probe up to it and put some 110 to the probe?

[N2IXK]

Originally Posted by stusnyder

I don't think its triggered. Supposedly if its in auto mode you should have a trace, normal mode won't show till it's triggered. Also the trigger light was not lit. Should I hook a probe up to it and put some 110 to the probe?

No need to use 110 (and dangerous to do so). Connect the probe to the scope's calibrator output, and you should get a square wave.

When you press the beamfinder, can you use the X and Y position controls to center the dot?

What are the sweep speed and trigger source (not trigger mode) set to? Sure the scope isn't in X-Y input mode?

[stusnyder]

I got a vertical trace but no horizontal. If I pull out the delay sweep knob I will get horizontal just for a second, then goes back to just vertical.
Also no trigger light or ready light. Not sure if the bulbs are good going to check them tomorrow.

[stusnyder]

Originally Posted by stusnyder

I got a vertical trace but no horizontal. If I pull out the delay sweep knob I will get horizontal just for a second, then goes back to just vertical.
Also no trigger light or ready light. Not sure if the bulbs are good going to check them tomorrow.

Bulbs are good. Can get a horizontal trace, once it sweeps across the screen it's gone. Trigger light and ready light never come on. I think it's something in the sweep board. I know the guy that had it had it plugged in when he had a power surge that wiped out most of his furnace controls
Could also be IC u600 which I was told was a custom and hard to find. Just might look for a parts unit and try using 2 to make 1.

[stusnyder]

Messed around with this again tonight. When I press the "A" button or the "mix" button on the horiz display box I get a flash of horiz line and then nothing. Still no trigger light or ready light. I got the probe hooked up to the speaker leads on a radio. got a thin vertical trace, thats it.
Anybody got any suggestions? This thing is way over my capacity.....