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Old 25th Jun 2013, 8:46 pm   #1
davidgem1406
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Default Tektronix 465B Scope - Some problems.

I have recently acquired a Tektronix 465B scope. Although it is in working order on running it and making some checks I have found some problems.

I will run through them, also there are pictures for all but one item.

1/. Not a fault really but something that threw me until I read the service manual. Although the vertical Volts/Div switches are marked up to 50V per Div the 3 top ranges 10, 20 & 50 V/Div are not usable. The switches do not rotate any further than the 5V/Div position. I found that rather strange, why mark them up to 50V/Div? (Image 002)

2/. The two traces are fuzzy with the Astig and Focus controls set to their best positions. Image 001)

3/. With a slow timebase it can be seen that the spot is distorted. The Focus and Astig controls change the shape of the spot more than focus it. (Images 3 & 3a)

4/. With an input signal to the vertical inputs the fuzzy traces can clearly be seen. (Image 4)

5/. The effect of the Focus control shows distortion quite clearly. Rather more than just defocusing. (Images 5 & 5a)

6/. The beam find does not show a clean round spot, it shows a short line with distortion at the centre of the screen. (No Image)

I was wondering if I may have a dirty/faulty power supply?

Would be grateful if anybody could point me in any direction regarding the above faults.
Also of any known faults that I should look at.

I have the service manuals, but it would be good to have the operators manual if anybody knows where this may be found.

Thanks
Dave.
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Old 25th Jun 2013, 8:47 pm   #2
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Default Re: Tektronix 465B Scope - Some problems.

Balance of the images for the above thread.

Dave
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Old 25th Jun 2013, 9:18 pm   #3
Alistair D
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Default Re: Tektronix 465B Scope - Some problems.

1) Try shorting the body of the input BNC socket to the ring at its base, something will happen. The idea is that if you use an X10 probe with a shorting clip fitted the V/div markings will be correct for the probe.

Most if not all of the other faults are probably due to the 5500uF cap that smooths the 8.5 Volt supply rail.

Al
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Old 26th Jun 2013, 12:31 am   #4
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Default Re: Tektronix 465B Scope - Some problems.

Hello Al,

Thanks for the reply,

Well I had to laugh at that one, would never have know that. I think it is quite clever really.
Never heard of a shorting clip being fitted to the BNC end of a probe, something new I have learned.

I will take a look at the capacitor and try a replacement if i have one.

Will have to find some better diagrams as well. I have 2 copies of the manual that turned out to be identical. The diagrams are a mess just been scanned in bits with parts missing so impossible to link them up to make a decent diagram. Same applies to the board layouts, fault finding charts and block diagrams.

Thanks
Dave.
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Old 26th Jun 2013, 12:45 am   #5
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Default Re: Tektronix 465B Scope - Some problems.

Tektronix carried the probe range switching a stage further on the 485 scope. There were 3 lights that could cope with X1, X10 and X100 probes. X1 was open circuit on the switching ring. X10 had one value of resistor fitted and X100 had an even lower value. I presume that only Tek's own probes had this facility. It would be interesting to find out if Tek, or anyone else, produced an adaptor to allow the use of third party probes.

Edit: I downloaded my copy of the 465 manual from the bama site. The quality seems to be OK.

Al
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Old 26th Jun 2013, 1:01 am   #6
davidgem1406
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Default Re: Tektronix 465B Scope - Some problems.

That's interesting never know of it before.

The manual I have came from the same site. I have just found out that the circuit for the power supply is missing, only the transformer being shown.
Also the board layout has only half the board available, in this case the wrong half.
The other half is the adjustment positions but no component numbers shown.

Project now on hold pending finding the diagrams, unless i suddenly feel brave.

Dave.
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Old 26th Jun 2013, 7:13 am   #7
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Default Re: Tektronix 465B Scope - Some problems.

Tek didn't get the probe sensing thing entirely right. I use a 50:1 resistive probe which works on 50Ohm terminated inputs on some of their faster scopes. It has the coded resistor contact on it, but the scopes get the ratio wrong.

The 50 Ohm switched termination is one thing missing on the 465 family, that is there on the rival HP1740.

David
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Old 26th Jun 2013, 10:50 am   #8
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Default Re: Tektronix 465B Scope - Some problems.

I have now looked at the 8V supply, in fact all of the 5 supplies and they are all clean. There is less than 5mV of muck sitting on any of the rails.

Could it still be the 5500uf cap on the -8V rail at fault?

Dave.
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Old 26th Jun 2013, 11:24 am   #9
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Default Re: Tektronix 465B Scope - Some problems.

David, try and get hold of the proper manual for your 485 as a priority, check the serial number for the correct manual.
Yes it could well be the -8v cap, I had a similar problem with a 475, and just tacking on a good 6800uf (doubt you will find a 5500 of the right shape)wont do, a good quality, low esr one it will have to be. Be extremely careful desoldering, as if its anything like the rest of the 46x series, its a dual sided pcb and you will damage it, if you are careless. Use a vacuum desoldering tool, not a cheap pump type.
Bill
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Old 26th Jun 2013, 1:26 pm   #10
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Default Re: Tektronix 465B Scope - Some problems.

Hi Bill,

The only place I can find to obtain a proper/original manual is the states and they are asking ridiculous prices for them, plus up to $100 for postage.

However I found somebody in Europe doing them on CD in pdf and guarantee they are 100% scans just as the original would have been. There are sample pages that can be downloaded. 1 CD on order.

Mine is a low serial number being 10874. Taken from the only label on the back and that being an RAF test label giving date of test, renewal date and serial number.

As for vacuum de-soldering tool, that's just way to expensive for my budget, but i will check again. Nice thought though.
I'm usually pretty good at removing components from boards including double sided and multi layer using a solder sucker.
They are indeed a double sided boards in the 465B.

Dave
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Old 26th Jun 2013, 2:43 pm   #11
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Default Re: Tektronix 465B Scope - Some problems.

If you don't mind pdf, try here http://artekmanuals.com/

These are non-free but from experience they do their own high quality scanning ...

dc

PS check you get the one that matches your serial number

Last edited by dave cox; 26th Jun 2013 at 2:45 pm. Reason: PS
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Old 26th Jun 2013, 3:19 pm   #12
davidgem1406
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Default Re: Tektronix 465B Scope - Some problems.

Hi Dave,

Thanks for the link I will check that out.

I have now removed the original 5000uf capacitor and replaced it with 3 x 2200 paralleled up, that's all I have available at the moment.
However it has made not the slightest difference in the trace quality it is still just as fuzzy and the same distortion occurs when the focus pot it adjusted.

I would have at least expected some change in things if the original capacitor was the cause of the problems.

Any comments welcomed.

Thanks
Dave.
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Old 26th Jun 2013, 3:40 pm   #13
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Default Re: Tektronix 465B Scope - Some problems.

If the original 5000uF cap is now out, can you measure its value and ESR? That should give a pretty good indication of whether it was at fault. Also, if you still want a paper manual, you could try Telford Electronics. I have got a number of HP manuals from them covering the right serial number range for my kit, and I believe they also had Tek from when they used to do calibration. Cost will probably be around 25 at a guess.

Mike
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Old 26th Jun 2013, 4:17 pm   #14
dave cox
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Default Re: Tektronix 465B Scope - Some problems.

The quick way to check for ripple in the trace is to set the trigger source to line and feed in a signal close to 50Hz. If you just have 'ripple' you should see a clean trace that just wobbles up and down a bit at the beat frequency.

However, to me, it looks like you have a bit of oscillation or breakthrough. Try working your way through the faster time-base settings (and variable) to see if you can get a beat frequency to identify the interference frequency (if there is one).

Your 'single spot' test, to me, would seem to indicate that its coming into the XY plate drivers, this is typically fed from +/- 50-150V rails. In my experience, this area is mighty sensitive to any interference. Is it me, or does the second 'spot' picture look a bit diagonal ? If so then it could indicate some interference common to X and Y.

dc
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Old 26th Jun 2013, 4:43 pm   #15
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Default Re: Tektronix 465B Scope - Some problems.

Dave, main smoothing cap failure is becoming very common on these scopes now, and the interference can be coming from a number of sources. You need to measure the psu rail outputs with another scope. Check each rail for ripple and take it from there using the data indicated in the manual. If the ripple is 50hz its the caps, if its 100hz, its a partial failure in one of the bridge rectifiers, these are common failures. I doubt that 3 caps in parallel will have a sufficiently low esr for the demands of your scope, use the best quality you can obtain, the originals were Sprague, and they are very good, rated for 25000hrs use at 85deg.
Caps of this quality are not cheap. These scopes were very expensive when new, and this is just one reason why.
Bill
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Old 26th Jun 2013, 5:17 pm   #16
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Default Re: Tektronix 465B Scope - Some problems.

Hi,

I've got a 465B manual so if you can't find anything else I could do you some hi-res scans of the bits you need.
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Old 26th Jun 2013, 5:45 pm   #17
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Default Re: Tektronix 465B Scope - Some problems.

Hi Mike,

I have no means to measure the value or the ESR of the capacitor.

The manual I have coming on CD in pdf format if that is good then im quite happy with pdf as i can print off any parts i wish.

Hello DC

I will go through all the supplies again and check the ripple. There is more than just ripple there but it is all below 5mV.
I will try to identify the other frequencies involved.

Yes the second picture of the spot shows it distorted and that is the effect of adjusting the Focus or Astig controls.

Hello Bill,

I will check all the power rails for ripple, i have another scope i can use.
Yes I have looked at Sprague as replacement and the price is just out of control, cheaper to by Gold bullion.
I found 1 capacitor on our favourite auction site said to be low ESR and 85 deg. C

Hi Dickie,

Thanks for the offer I need the board layout covering the power supplies and the circuit diagram for the same. Im using the 465 at the moment as they are better than the 465B I have.
I have the whole thing coming now on CD in pdf format, just hope its as good as they are saying.

Thanks to all,
Ill be back
Dave.
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Old 26th Jun 2013, 8:58 pm   #18
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Default Re: Tektronix 465B Scope - Some problems.

Dave:

As you have a second 'scope,. you might get a better handle on where the problem arises by switching off the sweep and centering the beam (as you have in one of your photos), then check for signals (relative to ground) on both Y and X plates individually. If there's no "noise" on the deflection plates, you're left with possible EHT and collimation issues. Oh, and check it's not some kind of mains-related problem by setting the scope trigger to "Line" and having a look at 50mS/div.

PS: I assume the screening cover is in place over the EHT section?

John
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Old 26th Jun 2013, 10:18 pm   #19
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Default Re: Tektronix 465B Scope - Some problems.

Just had a look at my manual, unfortunately the HV and tube sections are missing. As a guess I would think that the focus and brightness circuits are fed from an inverter. Smoothing failure here would put ripple on the focus voltage so the spot will never reduce beyond a certain diameter. One of the other pictures shows brightness variations over the trace length. This would occur when the sweep speed is similar to the inverter frequency.

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Old 27th Jun 2013, 12:19 pm   #20
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Default Re: Tektronix 465B Scope - Some problems.

Hi John,

I have not done as you suggest as yet, I am concentration on the power supplies for the moment but will try to do that later today.

What is collimation referring to? the definition for this, from a web search, is referring to the alignment of optical devices.

Yes the screening is in place.

Hello Al,

Yes those parts are missing from the copy I have as well, load of junk as far as all the diagrams go. I have another copy on CD coming.

The variation in trace brightness is not actually happening, it is the camera shutter speed, trace speed and the light causing it. It is even more pronounced in the pictures that accompany this post as there was more artificial light.


I now have the result of the checks made on the power supply outputs.

First I did manage to make a basic ESR check on the 5000uf capacitor using information found from a net search. This used a signal generator and a scope to view the output.
The result was that the 5000uf capacitor looks to be good. I have however a new 6800uf cap on it's way, this may or may not fit.
I did look to see if an original was available from QService but they are nil stock.

-8V rail with a 4400uf capacitor used was showing 100Hz @ 50mV looking like the bridge rectifier has partly failed, this is also very hot. (Image_a Top trace, the lower trace is just 100Hz from a signal generator for comparison)

+15V supply shows 2mV with HF (Image_b top trace) The bridge rectifier is also very hot.

+5V supply shows 2mV also with HF (Image_b) Again the bridge rectifier is very hot.

+110V supply shows 15mV @ 100Hz sawtooth with about 2mV of HF (Image_c)

+55V rail 3mV mixed with HF, looks like a mixture of 50Hz and 100Hz. (Image_d)

It now looks like a major strip down to replace some of the bridge rectifiers, at the very least the one for the -8V supply.

Ignore the variations in the trace brightness in the images, it is not really happening. It is the result of the trace speed, camera shutter and light.

Dave.
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