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Old 3rd Jul 2013, 8:10 pm   #41
davidgem1406
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Default Re: Tektronix 465B Scope - Some problems.

Hi David, (Radio Wrangler)

Yes the astig has much the same effect as the focus pot, just makes it a little worse at either end of travel or a little better at around the centre point but depends on where the focus pot is set.

I will look at the deflection plate signals, photograph them and post here.

Thanks
Dave
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Old 3rd Jul 2013, 8:22 pm   #42
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Default Re: Tektronix 465B Scope - Some problems.

Make a note of which cables go where, and with the scope switched off, disconnect all the coax cables toward the rear of the Y amp board (they are the ones with the little gold plugs and sockets on them) Make sure the ends don't short out on anything.
Then switch on, and you should have the timebase running, but no signal influence from the Y amps. See if its any better.
Bill
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Old 3rd Jul 2013, 8:44 pm   #43
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Default Re: Tektronix 465B Scope - Some problems.

Hi David, (Radio Wrangler)

The picture of what is on the deflection plates. Top trace is Vertical and bottom trace Horizontal. Scan speed 10mS, Horizontal input at 50mV/Div.


Hi Bill,

Ok I will do that. Back latter.


Dave
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Old 3rd Jul 2013, 8:50 pm   #44
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Default Re: Tektronix 465B Scope - Some problems.

OK somecrt shots of a warmed and running 465B

First is a dim focused spot, then a brighter one. These tubes are not as fine at focusing as my HP1740 and a far way from my old HP180 frames, but the 465Bs are nice usable scopes and I have a pair of them in working order.

Next up is the anticlock extreme of the focus control giving a sort of barrel shape. finally the clockwise extreme giving a disc.... and you can also see the mesh being imaged.

I was using an Elicar 90mm macro lens, so they each cover only the centre four squares of the crt.

And my spare 465B produces similar spots.

Hope this helps a bit,

David
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Old 3rd Jul 2013, 9:01 pm   #45
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Default Re: Tektronix 465B Scope - Some problems.

OK, so you have about 25mV p-p on the vertical plate and such a CRT might be something like 4 volts per division. This would wobble your spot 25/4 milli-divisions so 0.00625 of a division.

This is just a guess at the deflection sensitivity (and it is normally the plate-to-plate differential voltage), but you could easily put a signal in, set it for 1 division peak-to-peak, and measure the plate voltage again. Compare the result to 25mV p-p and you'll really know if the deflection system is wobbling the spot.

David (designed parts of an HP scope in a previous life)
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Old 3rd Jul 2013, 9:03 pm   #46
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Default Re: Tektronix 465B Scope - Some problems.

OK somecrt shots of a warmed and running 465B

First is a dim focused spot, then a brighter one. These tubes are not as fine at focusing as my HP1740 and a far way from my old HP180 frames, but the 465Bs are nice usable scopes and I have a pair of them in working order.

Next up is the anticlock extreme of the focus control giving a sort of barrel shape. finally the clockwise extreme giving a disc.... and you can also see the mesh being imaged.

I was using an Elicar 90mm macro lens, so they each cover only the centre four squares of the crt.

And my spare 465B produces similar spots.

Hope this helps a bit,

David
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Old 3rd Jul 2013, 9:10 pm   #47
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Default Re: Tektronix 465B Scope - Some problems.

Hi Bill,

Well I did that disconnected all the small coax connectors but i still have an input to the Y plates if I supply an input signal.
So at this time there is no difference in anything.

All those coaxes are going to the scan board or the main board.

As far as i can tell the Y output board is connected to the board with the attenuator switches, and vertical mode switches.

There is just the 1 flat multi-plug connecting the output board to the rest of the Y system.

Dave
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Old 3rd Jul 2013, 9:19 pm   #48
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Default Re: Tektronix 465B Scope - Some problems.

Hi David,

Thanks for the pictures.
Your dimly focused spot is looking far better than mine. The rest of them are far difference to what I am seeing.

I would expect the focusing to far better than mine is showing.

At the moment the Telequipment puts the Tek to shame, it focuses absolutely pin sharp.

Dave.
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Old 3rd Jul 2013, 10:09 pm   #49
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Default Re: Tektronix 465B Scope - Some problems.

Dave, we need to find out the source of the interference, personally I would remove the y pre-amp and input selector pcb, so that you are left with just the timebase, which will still operate. This also gives you the opportunity to properly clean the switches. I can photocopy the 465 manual y pre-amp removal procedure and send it to you, if you pm me your email address. Obviously there will be some differences, but if you hit any snags, you can work round it. If the interference disappears, you will know where to concentrate your efforts.
Bill
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Old 3rd Jul 2013, 10:12 pm   #50
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Default Re: Tektronix 465B Scope - Some problems.

Hi Bill,

Yes I could do that, at least it will give some answer to things.
I have the 465 Manual so no problem there, thanks.

Also I will check the 465B manual it may have the written procedure anyway.

That will keep me bust for a while I know.

Dave.
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Old 3rd Jul 2013, 10:19 pm   #51
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Default Re: Tektronix 465B Scope - Some problems.

I think the noise voltages on your plates say that your fuzzy trace isn't due to hum, ripple or noise, so I'd start checking the voltages on all the CRT electrodes.

One nasty possibility is internal damage to the CRT due to a bad knock.

Can you see the ghost spot? Set the timebase sweeping the spot across the screen on its slowest range, 0.5s/div and make the spot rather bright. You should see a dim ghost cross the screen at twice the speed of the spot. It is always about twice the distance from the centre that the spot is (and in the same direction) In my 465 it looks like a thick doughnut about 1.75 divisions in diameter.

It's an image created by the post-deflection accelerator screening dome-shaped mesh.
Its presence shows that the electron optics around the mesh are OK.

David
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Old 3rd Jul 2013, 10:31 pm   #52
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Default Re: Tektronix 465B Scope - Some problems.

David (Radio Wrangler), Ive seen this fuzzy trace problem on these scopes so many times now, that you end up convincing yourself its the tube. Ive had a 'soft' tube, but not one with internal damage. (Im not saying that's its impossible, but I'd like to rule out everything else first)
Bill
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Old 3rd Jul 2013, 10:38 pm   #53
Leon Crampin
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Default Re: Tektronix 465B Scope - Some problems.

I've been following this thread with interest as a confirmed Tek admirer and user.

Why not disconnect the deflection plates and join x to x' and y to y' (on the tube) with short pieces of wire? This should eliminate the possibility of noise or interference giving a thickened trace. If the EHT system is giving all of the correct electrode voltages, a CRT fault remains an unfortunate possibility.

Tek portables can suffer from loose screws securing pc assemblies which also double as earthing points for the tracks. Likewise, any loose fixings on (by now) slightly corroded or tarnished screens can give this effect. Also, the Fairchild plastic "TO-18" devices so beloved by Tek are non-hermetic and end up noisy or faulty. Replace with metal can devices. Finally, check the decoupling to the EHT oscillator (47uF from memory).

The 465B was my all time favourite portable work horse - used in the field in unspeakable conditions, in the rain and powered from a diesel generator. Impeccable performance at the time.

Best of luck with your problem.

Leon.

David, I'm afraid for me, Tek were the King of 'scopes but my H-P 41 holds a similar position as a problem solving machine. Mine has worked impeccably since about 1980. Both organisations have a proud history of achievement.

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Old 3rd Jul 2013, 10:40 pm   #54
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Default Re: Tektronix 465B Scope - Some problems.

Yes I have that Bill. It is more like a circle/ring than a spot and overtakes the spot at the centre of the screen.

Never noticed that before.

Dave.
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Old 3rd Jul 2013, 10:56 pm   #55
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Default Re: Tektronix 465B Scope - Some problems.

Good idea Leon, but if you are going to do this, be very careful in removing the crt connections to the x and y plates.

It may also be worth checking this: a while ago I had a very similar problem causing blurred trace and distorted spot, and this was the solution I posted on Tek usergroup:-

I had narrowed the fault down to the A/B sweep generator circuitry and checking
the voltages around that circuit revealed +29v on the collector of Q1096, when
it should be about 13v, I substituted Q1096 with an alternative with no
improvement. The voltages around Q1090 were also incorrect and it appeared this
N-channel jfet was faulty.I didnt have a direct replacement, but one from a
scrap board from British scope cured the fault and restored correct operation. I
dont know why this transistor had failed but it had, causing major problems on
both timebases.

Dave,you have the 465 manual, find that fet, and find its cousin in the 465B, you may just be lucky!

Bill

Last edited by maninashed; 3rd Jul 2013 at 10:58 pm. Reason: grammar
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Old 3rd Jul 2013, 11:13 pm   #56
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Default Re: Tektronix 465B Scope - Some problems.

I will try what Leon suggested about joining the plates together. I wont however try to remove the connectors from the CRT pins I will unsolder the wire connections at the PCB.
I have just looked at them 1 pair is dead easy to do the Y is rather tight on space but it will be done.

I can then put them back 1 pair at a time, maybe that will help locate what is going on.

Dave.
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Old 4th Jul 2013, 7:08 am   #57
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Default Re: Tektronix 465B Scope - Some problems.

Shorting the plates will determine whether it is deflection of the beam or whether it's a focus problem. Only one pair need be shorted, because if it's noise ingress, shorting the Y plates will reduce the fuzziness in the Y dimension and should leave a horizontal line.

I've seen a lot of CRTs with internal damage due to shock... all deliberate! There's a military shock test that involves a controlled drop, and virtually no electrostatic deflection CRT can pass it. The mass and cantilevered support of the deflection plates is a weak point. Protecting scopes from knocks is a very good idea.

David
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Old 4th Jul 2013, 12:26 pm   #58
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Default Re: Tektronix 465B Scope - Some problems.

I have now disconnected the plates from the output stages, Y1 and Y2 are joined and X1 is joined to X2.
That really hasn't changed the problem, the spot is fairly large with a lighter glow round it and will not focus down.
The focus and astig controls have much the same effect as before, just distorting the spot as shown by the images in post #39.

Don't know if putting some + voltage on the plates may help, say from the +55V rail. I seem to remember from many years ago that CRT's did not like the plates to be floating, maybe different CRT's back then.

I will put the X connections back and see what gives then.

I forgot to mention that the spot is pulsing at a regular interval. Just realised, whilst writing this, it is something picking up the timebase frequency as reducing the time period pulses the spot faster. Turn the timebase off and it stops.

May be relevant, may not.

Dave
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Old 4th Jul 2013, 1:03 pm   #59
Leon Crampin
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Default Re: Tektronix 465B Scope - Some problems.

Connect the shorted plates to one of the connections to the deflection amplifiers - x or y as appropriate. The plate pairs will then have a leakage path to earth and also be held at about their operating potential.

The tube's not looking good.... (but check that EHT oscillator supply decoupler - that stage makes quite a racket as it's powerful, having to also supply the tube heater).

Leon.
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Old 4th Jul 2013, 1:07 pm   #60
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Default Re: Tektronix 465B Scope - Some problems.

Dave, that will be the blanking pulse, it switches the beam off when it returns. That is normal.
Have you checked the details of post 55?
I'm not sure if leaving the deflection plates floating with have any adverse effect.
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