help with my scope

[lokeycmos]

i have a tecktronix scope model 564. last night when i turned it on i hear a soft pop sound and a flash on the side of the scope. but it still operated. the same thing happened this morning, it still worked. the wierd thing is that the power indicator was still on even though the switch was in the off position. the power switch feels solid with no play in it. now the scope wont power on at all. i took the side off, and found a fizzled capacitor. could this single cap be the cause of my problems? also, if you look at the pic of the side i attached, i noticed a few neon bulbs as part of the circuitry. what are these for? what do they do? thank you!

 

[bigal_scorpio]

Hi Lokey,

Yes the cap could be the cause. Caps (electrolytic) cause many problems when they get old or or used in hot situations, they dry out!

As for the scope not powering on I would be looking for a fuse gone. But I would be checking ANY large caps and if you have replacements just swap them out. Most likely they will all be bad to a degree. Check the state of the components near the cap that leaked too, sometimes a blown cap can take other components with it.

Al

 

[Reloadron]

Do you have the manual? The neon bulbs are likely between the CRT Cathode and Grid and placed in series with each other. They act as a clamp if the cathode and grid voltage difference exceeds their ionization level. If you have a manual start troubleshooting with the low voltage power supply after you replace that cap. However, you mention a flash and the pictured cap does not display any charring that I see? Leaking yes, but no signs of the flash.

If you need a manual The Boat Anchor Manual Archive can get you going.

Ron

 

[cowboybob]

If you do not have a complete manual for the 564 then here's a Free manual with schematics.

Page 76 has the power supply schematic.

The manual also has pictures of the guts. The neon bulbs are listed on page 65 and in the schematic on page 80.

B856 &B857 appear to be acting as voltage regulators for the biasing (≈90 - 100VDC??) of the first grid of the CRT, which controls the electron density of the CRT beam on its way to being focused.

<EDIT> Wish I typed faster. Just repeated what ron said above.

 

[large_ghostman]

that looks like a nice solid scope i was going to post a link to a manual but its already been done
lg

 

[dr pepper]

The cap has taken a while to get like that, the photo looks like its been there a while, the scope would probably work better with it replacing.

Check your power switch, maybe one or more contacts have welded ond others have opened (assuming it has more than 1 contact).
You could temporarily link out the switch to get the scope powered.

 

[KeepItSimpleStupid]

If you need more help than we can provide, join the Tekscopes group on Yahoo. **broken link removed**

There are some very knowledgeable people there including past employees at Tektronix.

Both suggestions, that that cap needs to be replaced and a possible broken power switch (fused on) seems valid. Look for other suspect caps too. Electrolytics are the most likely type to need replacing.

 

[lokeycmos]

the bad cap is in the power supply section. i circled the bad cap. is there any other possible parts it may have damaged down the line? there is definately something wrong with the switch. i get 120v up to it, but nothing out. at the green X's im measureing 1.3 ohms. doesnt that seem a little low for the primary? thnx

 

[KeepItSimpleStupid]

The transformer is probably OK, but I would check the 10 ohm resistor and the diodes. The tube might have been stressed too.

Once you get it to work, consider replacing the electrolytics

Bringing the scope up on an isolated variac, variac. or even a 100 W light bulb in series with the power line would be beneficial. The light bulb may have to be a higher wattage. What's the power consumption of the scope in watts and the line voltage?

 

[bigal_scorpio]

Did you notice there are 2 separate but identical parts to the supply?

The cap in question has a sister that will likely be just as bad, its directly below it about an inch down on the schematic. I would definately change BOTH caps before even trying the scope.

Al

 

[lokeycmos]

The transformer is probably OK, but I would check the 10 ohm resistor and the diodes. The tube might have been stressed too.

Once you get it to work, consider replacing the electrolytics

Bringing the scope up on an isolated variac, variac. or even a 100 W light bulb in series with the power line would be beneficial. The light bulb may have to be a higher wattage. What's the power consumption of the scope in watts and the line voltage?

maximum of 250 watts at 117v

 

[KeepItSimpleStupid]

Then I might want to use (1 to 3 light 100 W light bulbs parallel) and placed in series with the AC line for start-up.

I do agree with replacing the similar cap.

 

[rumpfy]

Hi lokey,
I too have a 564 and also the manuals. My cro has the storage tube as well, and the 3B3 timebase and 3A6 wideband vert amp.
I have had trouble with various sections of the cro over the years and have done some extensive re-design.
I think the 'pop' you hear is flashover in the HV circuit. Mine has been doing this for a long time, but when it warms up, its OK.
I have looked at the crt socket and this is badly affected by corona discharge across the face of the phenolic moulded crt socket and the crt tube pins are corroded. This cro goes back to the late 1950's so to have these crt's running 50 years later is a credit to the designers.
Nevertheless, it is possible to keep it running.
The major deterioration I find is in the degradation to the socket and pins due to corona discharge.
I have redesigned the power supply to replace the 6080 series regulator tube with CMOS power transistors. I have also had failures with the tunnel diodes in the timebase and have redesigned the delaying timebase to use a LM339 IC's. Many of the 2N2207 transistors have failed and I've redesigned this part of the circuit to use modern Si transistors.
I know of an old tek employee who has heaps of this stuff from his days at the factory, but he is a purist who insists that ALL the tek stuff be stock standard. I'm in OZ and haven't got the spare parts availability like he has. So I have to improvise. I need the cro to be working as it is used often. I don't keep it as a museum piece.

 

[dr pepper]

You can still get anti corona lacquer to spray on crt high voltage stuff, its more of a prevention than a cure though.