Busted OScope, I think the transformer is fried!

[Andrew Davie]

No, i resoldered the wires.

Ah, the beauty of ambiguity. Steve probably meant "Have you put the plugins back into their original positions" or something similar. Not "Have you got new ones".

[Steve Anderson]

OK, you won't get anything other than a dot on the screen without the plug-ins fitted. All of the functions of the scope are in the plug-ins. The main chassis is not much more than a power supply.

If you feel confident that you've found the problem in the plug-in, insert the right-hand one only (the timebase), you should get a horizontal line if it's OK, if not fiddle with the position, triggering and stability controls (if fitted).

If it appears to be OK, replace the other. Let us know how you get on.

Steve A.

Andrew, yep, a bit vague...I meant have you restored the original plug-ins to their original positions?

[smeezekitty]

New problem!
High voltage arcking noise from CRT tranformer box.

[Steve Anderson]

New problem! High voltage arcking noise from CRT tranformer box.

BE CAREFUL!! THERE IS SOME 5000V AROUND THERE!!

Switch it off and leave it for a day for the capacitors to discharge, even so still exercise extreme caution!

Around all of the high voltage parts there's probably a build-up of 'dusty fuzz'. First thing to do is clean this off wherever you see it.

The manual I have has few photographs or drawings of the insides, but if it looks a reasonable job, open up the transformer box and clean that out too if it needs it.

Steve A.

[smeezekitty]

Ignoring the 5kv i opened the high voltage box to find and aluminum bar stuck in there.
I removed it but the CRT only works when you hold down sweep reset and the knobs are set in certain ways.
----edit----
The 5kv short may have fried a valve because V800 had a blue blinking glow

[Steve Anderson]

Ignoring the 5kv i opened the high voltage box to find and aluminum bar stuck in there. I removed it but the CRT only works when you hold down sweep reset and the knobs are set in certain ways.
----edit----
The 5kv short may have fried a valve because V800 had a blue blinking glow

Not knowing what model timebase you have it's not easy to help, but as a first guess make sure a switch probably marked 'Mode' or something similar is in 'Auto' or 'Normal', not 'Single' or 'Single Sweep'.

From what you've said so far it appears this thing has been bounced around quite a bit!

Valves/Tubes operated at close to their maximum ratings often emit a blue glow between the cathode and anode and as this device is used as a flyback EHT generator it sees quite a few hundred, maybe thousands of volts at the peak. If it is random and it happens without you touching anything then something is amiss.

If it only happens when you press the 'Sweep Reset' button, then this could be normal, but I can't see why.

The other thing to check is are the heater(s) or cathode(s) in V814 (12BH7) glowing? If you can measure the voltage of the anode of V814A (pin1) (also pin 1 of V800), it should be around +72V (say 50-100V)...this is tube circuitry!!

Steve A.

[smeezekitty]

I attached some pictures.

[smeezekitty]

Ok, i got dim CRT and the dot is blinking at the same speed as the tube.

[smeezekitty]

bump

[Steve Anderson]

OK, seems we're getting somewhere...

1) Have you re-inserted the vertical amplifier (left-hand plug in) or not? If not, don't fit it yet. If you have leave it in.

2) Set the controls on the 2B67 timebase as follows...

Position-centred.

Time/Div (big outside 22-position switch) at-2mSEC-

Variable-(smaller red knob concentric with above)-fully clockwise where it will click at the end-stop (a switch) The 'Uncal' Neon on the front of the plug-in should go out.

Mode-Normal (up)

Level-fully clockwise (free run) I think this is also another switch at the fully clockwise position, but not sure...memory not so good!

Slope +

Coupling-AC Slow

Source-Int.

That should give you a horizontal straight line right (or almost) across the CRT face. Adjust the 'Focus' and 'Intensity' controls for best looking line (top right main chassis front)

This timebase model doesn't use the 117V that is fed to it. Pins 7+8 on the rear connector of the plug-in shouldn't be connected internally.

Let me know the model no. of the left-hand plug-in. When this is fitted (if you haven't already) this might give a brighter trace with better focus.

Steve A.

[smeezekitty]

First, sorry for the bump.

OK, seems we're getting somewhere...

1) Have you re-inserted the vertical amplifier (left-hand plug in) or not? If not, don't fit it yet. If you have leave it in.

I have inserted it.
2) Set the controls on the 2B67 timebase as follows...

Position-centred.

Time/Div (big outside 22-position switch) at-2mSEC-

Done.

Variable-(smaller red knob concentric with above)-fully clockwise where it will click at the end-stop (a switch) The 'Uncal' Neon on the front of the plug-in should go out.

The small light in front faded out.

Mode-Normal (up)

Done
[/quote]
Level-fully clockwise (free run) I think this is also another switch at the fully clockwise position, but not sure...memory not so good!
[/quote]
Done

Slope +

Done

Coupling-AC Slow

Source-Int.

Done & Done

That should give you a horizontal straight line right (or almost) across the CRT face. Adjust the 'Focus' and 'Intensity' controls for best looking line (top right main chassis front)

This timebase model doesn't use the 117V that is fed to it. Pins 7+8 on the rear connector of the plug-in shouldn't be connected internally.

Let me know the model no. of the left-hand plug-in. When this is fitted (if you haven't already) this might give a brighter trace with better focus.

Steve A.

I see a very faint horizontal line that can be see with all lights off only.
Amplifier is a 2A63.

[Steve Anderson]

Right, seeing as you're getting a full(?) trace across the tube but very dim it's time to check out some resistors in the high-voltage part of the CRT circuitry. A dim trace is a good indication that the main chassis power supplies are at least somewhere near the correct voltages and the timebase is good.

Make sure the power plug is of the outlet for at least an hour before doing this.

Around the CRT are same high-value resistances, these 1960s items even for Tektronix are notoriously unreliable. You'll probably have to disconnect one end of each of the following resistors to obtain a true value. These are all on the main chassis.

R840, 1.2M
R841, 2M, high voltage preset on chassis.
R842, 12M...see what I mean about high values?
R844, 5M...Front panel focus control
R846, 2.2M
R835, 30M...wow!
R833, 2M, Front panel intensity control, might (or might not) have another resistor in parallel (10M) reducing its value to 1.7M
R834, 1M
Two more but sane values...
R836, 22k...but sometimes 56k!
R831, 100k

If they're within 20% of their nominal value all should be OK. Quite a few of the cheaper multimeters cannot read up to 30M, mine runs out at 40M. Nor sure what to do there. Simplest would be substitute it with three 10M/2W in series.

Even though very dim do the front panel focus and intensity controls do anything?

Note the position of the high-voltage preset, (R841) rotate it from one end of the track to the other a couple of times, return it to its original position.

I assume you do not have a high-voltage meter, to measure 3.5kV in this case as that would really help.

Steve A.

Looking through the 561B manual...it uses much saner resistor values and the two EHT tubes are semiconductors. It's quite a substantial change, leads to the impression that this was a 'problem' area.

[Steve Anderson]

A 2A63? Very unusual!...and in a way a shame for the usual way one needs to use a 'scope. It's a differential input module, not often seen and somewhat specialized. It can be used in a standard manner but its biggest drawbacks are its bandwidth which is only 300kHz and it's only single-trace.

For a lot of the more usual NBTV work it will do, but if checking out logic you might find it limiting. Plug-ins do pop up on e-bay so you might want to keep a lookout for these ones...

3A1, dual-trace 10MHz
3A1S, dual-trace, 25MHz

I suggest the 3A1 as the manual is available for download whereas I haven't been able to find a manual for the 3A1S...and 10MHz is plenty for NBTV and analogue FSTV.

But first I guess we need to get it working as is....

Looking through the manual for the 2A63 it too doesn't use the 117V fed to it so what was blowing the fuse might still be waiting to bite again unless the shorting wire you found was on the main chassis.

Steve A.

[smeezekitty]

I have a super cheap meter that only goes to 2 mega ohm and 1 kv.
I will try the stuff you said.

Even though very dim do the front panel focus and intensity controls do anything?

Make it dimmer.
----edit----
There is a discharge tube under the high voltage that is blinking twice a second.

[Steve Anderson]

There is a discharge tube under the high voltage that is blinking twice a second.

That certainly doesn't sound right. The manual I have for the 561A doesn't include any mechanical drawings or photos so I have no idea of the physical location of components. If you could identify the tube concerned that would help, i.e. Vxyz. or tube type, 6xyz.

Steve A.