Tektronix 465b oscilloscope CH1 & 2 issues

[ajgriff]

Originally Posted by ColinTheAmpMan1

If I remember correctly, some scopes can use a 100x probe and have the ability to light yet another lamp to indicate this.

Not directly relevant to the 465B but for those scopes that can detect 100X probes a 5.6k resistor works apparently. See link in post #99.

Alan

[Radio Surfer]

Evening,

Just some brief responses to the various comments posted and some new thoughts.

Thank you for the comments on probes and how the additional light works on the Volts/Div selector, all very clever. If you recall I put the contents that came with the oscilloscope to one side whilst I cleaned the plastic\ leatherette top case. I've just had a look through to see if I had the correct type of 10X probe with the small pin. Unfortunately, I have the bag and data information sheet but not the probe. Instead I have 2 switchable 1X\10X probes, one from RS and one from Farnell but they'll be fine for me at the moment whilst I get to grips with the instrument. Along with these probes, I also have various adaptors and what looks like a clear replacement screen.

Thanks for the information on the prefix references to determine whether a US or Guernsey model, mines a Guernsey version, no 102223 dated 1979, is that an early or late model?

Those extra videos that Alan found really helped me understand the time delay function, I'd never have worked it out. I'm thinking of knocking up a simple wave generator, just something I can use to test the scope and my hopefully improved understanding of some of the key functions. I've got a selection of transistors, resistors and capacitors to make something basic but usable. I can look at something more advanced at a later stage.

The filter material has arrived, apparently a couple of days ago but was put on the microwave hence I didn't notice it, so thank you to Nymrod121. That's a small job for tomorrow.

Tomorrow is looking dry in the morning but then a couple of days showers and rain, so I should have plenty of time for oscilloscope play.

Finally, Colin, I sent over my full details earlier so hopefully that's sorted.

Regards to all, Richard

[MrBungle]

That sounds about right. When you recieve a Tektronix scope it usually has a bag full of cables. You excitedly pull the bag open seeing three Tektronix probe instruction sets leap out. Within 30 seconds you find it's 3 corroded BNC cables, a BNC to Phono adapter, two RS probes which are broken and three Tektronix probe parts none of which belong to the probes which came with the scope!

Sine wave generators! Tektronix! My thing! I've been working on a "scope tester" board. This is a quadrature sine oscillator, two square wave generators, two integrators and two summing amplifiers all crammed into cheap LM358's and a few discretes. I'll do a forum post on it when I get time to finish it off. Preview, on a Tek 465 of course (this is the one that blew the HT immediately after Colin had my 475A and I returned to the project putting a temporary end to it - grr!): https://www.youtube.com/watch?v=xl61gMaxmMQ

[ajgriff]

Originally Posted by Radio Surfer

Thanks for the information on the prefix references to determine whether a US or Guernsey model, mines a Guernsey version, no 102223 dated 1979, is that an early or late model?

Just wondering where the 1979 date comes from Richard? The machines themselves aren't usually marked with a date, just some of the internal components.

I think it's generally accepted that production of the 465 began in 1972. Beyond that TekWiki states that the 465B was introduced in 1980 and another source suggests that the model was current until 1983 (catalogue dates I suspect). However, the first prints of the 465B Instruction Manual and Service Manual are both dated 1979. As mentioned in previous posts serial number information is sparse and unhelpful. My Guernsey 465B has the serial number 101888 so was presumably made prior to your scope.

All as clear as a view of the mainland on a foggy day!

Alan

[Radio Surfer]

Hello,

Rain stopped painting on Tiree, still 2 dry days is unusual these days. Tiree used to claim to be the sunniest place in Britain, based on the last few years I'm not sure that still holds. Last year it rained constantly whilst the rest of the country baked.

Back to the thread, Alan I remember seeing July 1979 marked on something, probably a component which as you say doesn't determine its date. Maybe a carry over component from the 465? So at least I know it was roughly between 1980 and 1983 and after yours!

Mr B, you should market that bouncing ball as a retro arcade game, takes me back to my younger days and all those classic games.

This afternoon, I'll make up a some sort of wave generator, depending on what I've got to hand, and test the scope out a bit more. Hopefully I can feedback results and any questions or issues later.

Regards, Richard

[Radio Surfer]

Evening,

Well I built something and it created a sine wave, so miracles do happen. Just a transistor, 5 resistors and 4 capacitors with an old defunct 9v battery out of the Hacker radio and we were there.

It's not what I would call in depth testing at this stage but I wanted to see as quickly as I could what is working, seemed odd and clearly didn't work.

Given that when I started this journey I couldn't even get a display, things have come on a long way in the last 10 days.

So here are the results of the first round of testing:

Both channel 1 and 2 are working, subject to the known faulty attenuator module, which thanks to ColinTheAmpMan1 a replacement is winging its way to Tiree as I type. At least I have enough at the moment to be able to test both channels with a signal. However, rather than list all the stuff that works, I'll focus on the areas that don't seem quite right or I've misunderstood something.

1) The horizontal position control works to centre the trace, but I've noticed that when a signal is applied the trace often needs to be re-centred. When the signal is removed, the trace needs to be centred again. Is that normal?

2) The various videos I have watched with regards to the Delay Time Position seem to show the A trace with an intensity that varies along the trace as the B trace is delayed by the Delay Time Position. Although the delay function is working as in the image below, I don't see a difference in the intensity, am I missing something? (Image attached).

3) When using the calibrator generated square wave to set up the probes, I notice that the top and bottom of the square wave gets progressively more blurred as the Volts/Div knob is turned to a lower setting and the trace is enlarged on the screen. It's not a sharp image as I would expect. A few photos are attached showing this. Any thoughts?

I'm not convinced the probes I've inherited are particularly good, one doesn't have the "grab attachment" so I have to hold the probe and naturally it slips when I'm adjusting the various buttons etc. The other has this attachment, but seems to create a "fuzzy" image every so often. I don't think it clips into the attachment particularly well.

So a few, hopefully, minor issues. All other buttons, knobs etc. seem to do as expected and some regular use should ease the stiff rotational knobs and keep the delicate contacts clean.

I realise that the scope will undoubtedly need calibrating as well, but for the purposes of this exercise in hopefully resurrecting it from the "barn scrap heap", I'm not too concerned about that (at least for the time-being!).

Trouble is, you can't help thinking that a a proper signal generator would be good, some decent probes, a quality variable voltage supply and suddenly we're on the slippery slope........

Until then, all the best Richard

[MrBungle]

Looks excellent. Nice work!

Regarding that slippery scope slope, be careful. I am trying to climb back up it at the moment. Many of us have succumb to the exponential test gear requirements

[Nymrod121]

Guilty as charged, m'lud

[ajgriff]

To see the the intensified portion of the trace the A INTEN button needs to be depressed and B INTENSITY adjusted accordingly.

The 465B's trace is not particularly sharp as these things go because of the way the CRT was designed.

I also suffer from TED (Test Equipment Disease) and will not admit to the exact number of ancient analogue scopes lurking in my vicinity.

Alan

[MotorBikeLes]

If you don't have scope calibration equipment, looking at the delayed timebase can be confusing. Many people have a (now redundant) colour TV sig gen. If you probe the input to the modulator, you can look at line pulses, or, with a slower timebase speed, the field pulses. Now bring in the delaying timebase and focus in on (say) the 8th line following the second field pulse. With a real analogue signal, there was a time you could examine the (rapidly changing) digital info of the teletext signals. I forget off hand which line after the field pulse they lived, but all good playground for learning how to use a dual timebase scope.
Les.

[ajgriff]

I hope the attached photos illustrate the point about the 465B's slightly fuzzy trace. The first one is the 465B and the second a Hameg HM 203-5 displaying the same signal using the same probe. Tried to ensure that all settings were identical and both screen shots were taken with the scopes in the same environment from the point of view of localised hash. Image resolution is limited by the forum's software and my photographic skills but I think the difference between the two traces is clear (or fuzzy!). I don't pretend to understand the physics behind why the Tek's CRT mesh produces this effect but apparently it does.

With regard to the horizontal shift on Richard's scope I guess that some adjustment is required somewhere as I can't replicate the effect using the panel controls. I've a vague recollection that there is a horizontal amplifier balance adjustment referred to somewhere in the manual's calibration procedures but I may well be wrong. On the subject of calbration, this is definitely not something to be undertaken lightly and really needs adequate equipment. There are one or two things that can be adjusted independently but in the main once you've started you've got to finish.

Alan

PS I really should be more diligent with scope screen cleaning.

[MrBungle]

Also don’t forget the vertical amplifier bandwidth is higher than a 20Mhz scope thus more noise. This leads to a probabilistic “intensity grading” of the trace. The 475’s are even fuzzier. Poke the 20mhz BW limit switch on the 465B and you’ll see the difference in sharpness.

[ajgriff]

That's true of course Mr B. I should have said that the 20MHz bandwidth limit was selected for the 465B photo.

Alan

[Radio Surfer]

Morning,

Wow, plenty of responses this morning, thank you for the comments, thoughts and late night testing.

The point of enhanced "fuzziness" as the vertical display is increased (my words and interpretatation) makes sense and my expectations may have been a little too high.

However, this morning I have had another look and have improved the display significantly. I hope the photos do this justice with the before and after shots. These show the square wave generated by the calibrator with 5mV vertical setting on CH1. To improve things I ;

1) cleaned and metal polished the U shaped calibrator bar. I noticed that was quite rough and on closer inspection could see quite a bit of light surface corrosion. I'm not sure if this was originally chrome plated, but it gave the appearance you often see when chrome begins to lift. If you look closely at the first photo you can just see the corrosion.

2) took off the "grabber" attachment ( probably got a more technical name) from the probe as this seems to be a bit dodgy at times and just used the probe to connect to the calibrator bar.

3) reset the focus with the square wave at the 5mV setting, easier to see when in focus.

4) adjusted the Astig turn screw setting very slightly as recommended in the service book. That's as much calibration as I'm confident doing at the moment

All in all a result. So hopefully, one of the minor issues dealt with.

On the point 2 above and probes. There are some interesting prices charged for some of these. If I decide to get a new probe is it like most purchases coupled with the laws of diminishing returns. In other words, there is a big difference between a cheap auction site Chinese £6 probe and a £30 probe, but relatively little between a £30 and £90 one? Keeping in mind what I'll be doing, i.e learning to use the scope and experiment. I'm just looking for something robust and reliable but don't want to "penny pinch" if spending a little more really helps out in the long run.

Now its raining again, I can justify some time looking at the other issues. I'll focus on the "highlight" part of the display using the various intensity settings. I'm not geting that at the moment, but hopefully the penny will drop. If you hear a dull thud from a northerly direction you know it has.

Until later, Regards Richard.

[Radio Surfer]

Listen out......THUD,

the old penny has dropped and the highlight function working with delay knob pulled out and the Delay Time Position adjusted to move the highlight.

This is good stuff. Hopefully, the photo shows this, and you can even just see the vertical line between the upper and lower trace which is normally invisible.

What else will today bring........

Regards, Richard

PS, "now where is that penny" as Frazer would say.

[ajgriff]

Excellent progress and the front panel looks like the scope has just come out of the box rather than years in storage. Puts mine to shame.

Alan

[MrBungle]

Looking good.

On probes, the cheap Chinese ones are rubbish. The second hand ones are mostly rubbish or broken. The new old stock ones are expensive. Even the new Rigol and Tek ones are rubbish.

Really good probes are really expensive. I think a proper set of Probemaster ones was going to set me back £200 or so.

Thus being a vertible cheap arse, I've found a compromise. These are made by Wittig and aren't particularly expensive. I've bought about 10 of these in the last couple of years and they do what they say on the tin. There's no spring clip for the tip but you can get decent ones from aliexpress.

https://www.ebay.co.uk/itm/153341055122

Seller is trusted and as said I've bought a lot of them!

A lot of the time I'm doing substitution based measurements so I've equipped myself with some T-pieces, 50 ohm terminators inline and end and attenuators however. That works better than probes for my requirements.

[Chris55000]

Hi!

Just a quickie one related to Tek 465/465B issues

Are the equivalent circuits of the unrepairable attenuator modules given in the Service Instruction Manual, and has anyone been able to make a working replacement from suitable close–tolerance "chip" resistors plus caps/trimmers off old ones?

Chris Williams

[MrBungle]

The equivalent circuits are not published as far as I know. You can reverse engineer the resistor values from the outside though with a bit of algebra. Remember doing some stuff with matrix determinants many years ago that magically solved these sorts of problems but can’t remember any more!

Building a replacement is probably dependent on finding the right resistor values which are usually weird in attenuators of any kind and not in any E series. You’d then have to validate that it does what it says on the tin so you’d need a pulse generator and constant amplitude generator and build a suitable test rig.

Whole thing gets complicated quickly so probably better to find a junker and steal the attenuators out of it.

If I see any around I’ll buy them up for parts stock.

[ajgriff]

Just to add to Mr B's comments I've been studying the manual which is headache inducing at the best of times so please don't take the following as gospel but at least I tried.

The attenuator modules are shown in circuit diagrams 1&2 as little boxes with C3*,C3* written inside the boxes and they are wired as if there are two trimmers inside each module. The modules are connected to resistors which are shown separately, as they are in the board diagrams as well. The resistors and their values/specs are listed in the main component parts list under the A3 attenuator board heading. However, the attenuator modules themselves (C3*,C3* etc) are listed separately as chassis parts with no component values or specs.

If Chris would like to have a look at the manual himself after consuming the necessary number of tablets, it is readily available as a free download from various sources.

Alan