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Old 21st Dec 2015, 4:17 pm   #1
ljdavek
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Default Tektronix 545 Oscilloscope fault

Hi all,
hope your all ok, I have this Tektronix 545 Oscilloscope that a friend gave me,

so i did try it out and did get a very bright green dot appear so seemed all good but then sort of vanished!! now i just get a sort of green smudge on the screen that moves about a bit when adjusting some of the knobs. I'm guessing some caps need changing could someone tell me where to start as there is a lot of stuff in this scope..

Thanks

Dave.
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Old 21st Dec 2015, 6:29 pm   #2
karesz*
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Default Re: Tektronix 545 Oscilloscope fault..

Hallo Dave,
Use please 6AL5W-Martins forum (and maybe these)_some times hi is here too...
Regards-Karl

Last edited by karesz*; 21st Dec 2015 at 6:40 pm.
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Old 22nd Dec 2015, 11:02 pm   #3
ljdavek
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Unhappy Re: Tektronix 545 Oscilloscope fault..

Hi, I've had a look and it won't change Select language to English so not much luck at the mo. Has anyone on here been inside one of these?

Thanks

Dave.
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Old 22nd Dec 2015, 11:23 pm   #4
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Default Re: Tektronix 545 Oscilloscope fault..

Hi,

The first step is to get hold of a manual (available free from the BAMA site). Once you have the manual check the voltages of the various stabilised power supplies. They are all referenced to the -150V line.
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Old 23rd Dec 2015, 5:20 pm   #5
dave cox
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Default Re: Tektronix 545 Oscilloscope fault

Then check the ripple !

dc
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Old 23rd Dec 2015, 5:32 pm   #6
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Default Re: Tektronix 545 Oscilloscope fault

Which Tektronix 545 model is it (545A or 545B) as they are quite different internally. The power supply is the first area to go through first. Unlike more basic oscilloscopes the 545 series oscilloscopes have quite a complex power supply using lots of valves and neon voltage stabilisers. Once you have the circuit diagram for the power supply, fault finding is not as daunting as it would first seem as it is easily broken down into several sections. Once the power supply is correct most of the CRT adjustment controls (focus, Astig, brightness ECT.) should work as intended.
The time bases can then be worked on with confidence that the CRT display is correct. You are lucky as it sounds like much of the oscilloscope is working in a fashion (EHT unit, CRT circuitry, power supplies for the CRT ECT.)
Christopher Capener
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Old 23rd Dec 2015, 11:30 pm   #7
n_r_muir
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Default Re: Tektronix 545 Oscilloscope fault

Hi,

The main difference between the 545A and 545B is the vertical amplifier. The A model used an all valve distributed amplifier and a delay line made up of a cascade of discrete L & C's, the B model used a hybrid valve transistor amplifier with a compact cable based delay line. The power supplies, CRT unblinking arrangements and time bases were much the same. Checking the power supply voltages and ripple voltages is the best way to start your finding.
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Old 27th Dec 2015, 12:33 am   #8
ljdavek
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Default Re: Tektronix 545 Oscilloscope fault

Hi now Christmas is out of the way thanks for help so far had no chance to look at the power supply at the moment. I do believe its the 545A as there is not any sort of transistors in this thing and it dose not seem to have any letters after the number!!

Thanks

Dave.

Happy new year to all on here....
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Old 27th Dec 2015, 8:55 am   #9
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Default Re: Tektronix 545 Oscilloscope fault

The 545A I think has a fatter ( over the length) CRT, something like 8" diameter. the 545B has a slimmer CRT approx 5" diameter.

What plugins/ vertical amplifiers does it have? These may help identify what version you have as will some pictures posted here.

The manual is free from either boatanchor manuals or elektrotanya, also lots of info and pics at Tekwiki.

Andy.
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Old 27th Dec 2015, 9:58 am   #10
cmjones01
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Default Re: Tektronix 545 Oscilloscope fault

There are three versions of this scope - the 545, 545A and 545B. If you have no letters after the number as you say, then you may have the original 545. If my memory is correct, one way to tell is that the timebases on the 545 had two knobs, one for time per division (1-2-5 microseconds) and another for the multiplier (1-10-100). The 545A changed that to the conventional single knob with all the different time scales on.

I have a 535A, the 545A's lower bandwidth brother. As others have said, check the power supplies first. The manual describes all the test points. The -150V is the most important as it's the reference for all the others (+100V, +225V, +350V, +500V).

Also check for finger trouble. What have you got the trigger controls set to? Try cranking the stability control all the way clockwise, which should force the timebase to run. Does the scope have neon indicators above the screen showing the beam position? If so, can you get each of them to light by twiddling the horizontal and vertical position controls?

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Old 2nd Jan 2016, 4:13 pm   #11
6AL5W-Martin
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Default Re: Tektronix 545 Oscilloscope fault

hello Dave,
1.) check -150V
first of all you have to check the voltages from the PSU, always !
And always at first the -150 volts bec. this is used for reference to provide all other voltages in that PSU. If there is another then -150V , there is a pot to adjust it, and if this will not help write here again. Adjust the -150V very exactly, <1%

Tell us if you have a running scope there, if yes check the ripple on the -150V also,
if you have a high voltage test head for the multimeter or VTVM?
if you have a valves tester?

2.) check all other voltages from the PSU

+100V
+225V
+350V
+500V

if possible give us a screen picture and of coarse the results of your test.

greetings from germany
Martin

! take care, the PSU is very powerful, life dangerous voltages !
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Old 2nd Jan 2016, 6:37 pm   #12
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Default Re: Tektronix 545 Oscilloscope fault

I can't remember if this applies to the 545, but it certainly applies to other Tek 'scopes of that vintage. All the PSU outputs 'track' the -150V rail, that one is the one you adjust. And adjusting it generally means recalibrating the entire 'scope.

So while you must check the -150V rail, do not adjust it if it is only a few volts off. If it is wildly out, then there is probably a fault in the -150V supply which needs to be corrected. But it if say measures -145V on your meter leave it alone, that is not the fault and tweaking it could mean a long night ahead...
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Old 2nd Jan 2016, 7:14 pm   #13
6AL5W-Martin
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Default Re: Tektronix 545 Oscilloscope fault

hello Tony,
I dont want to agree with that.
All mostly an old Tek was cared by the calibration service up to the day a man got it at home. And then never again calibrated. So you can be pretty shure that the calibration still needs the -150V. Many years later (without calibrations) there comes a problem, mostly tired 6AU6 in the PSU or a bad elko, and the problem is present.

The +100 is also needet to heat the tubes in the plugins (75V of the 100, the rest 25V will heat some small tubes in the frame), it must be exactly.
The +225 have to be exactly.
The +350 can drift a little without getting problems.
And the +500 is a serial Voltage, can be a +150 what is groundet at the +350V, see manual. Can also drift a little.

The old Tek must be set to -150V +-1V, then checking the other voltages. When the +225 is to high, mostly the double triode there what is driving the 6080, is tired, and the other voltages use as drivers 6AU6 what also can be tired. The big 6080 is mostly still OK. In the -150V the Gas stabilizer tube is to check if the light is on, around 85V
tired 6AU6 can be localized by swapping with another 6AU6, there are some of them.

greetings
Martin
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Old 2nd Jan 2016, 8:23 pm   #14
TonyDuell
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Default Re: Tektronix 545 Oscilloscope fault

I think we are misunderstanding each other...

The -150V supply _is_ critical, and it does affect the calibration of the entire 'scope. But if the 'scope has been calibrated with the -150V supply at slightly the wrong voltage then setting it spot-on with a well calibrated meter could actually make things worse.

If the -150V supply is right then the others should be too.

In any case, a slight error in any of the supply voltages (no, not a supply entirely missing due to a component failure) will not cause the problems the original poster has.

So I suggest checking the supply voltages as the first thing to do. No piece of electronics will work without a power supply. If one is missing or very incorrect in voltage then find out why. But do not at this stage adjust the -150V trimpot in the hope that it will get the thing working. It won't. And remember that +/-1V in 150V is an accuracy of better than 1%, and a lot of cheap DMMs will not manage that.
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Old 2nd Jan 2016, 9:20 pm   #15
6AL5W-Martin
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Default Re: Tektronix 545 Oscilloscope fault

Tony we are in the same way

I think the problem is sitting in the high voltage area of the scope.
But the measuring of that requires correct voltages from the PSU, that thing is connected allover (not shure in moment, -150, +100, +225 and the cold primary end of the HV transformer at +350 or +500V)

He have to test the kathode of CRT, high negative voltage, if that is wrong, he have to check the isolation resistance of the filament wire from CRT related to ground, chassis.

The most possible problems here are a bad isolation in the filament wire of the transformer, or that must be recapped with a small pack of 10nF/3kV ceramic disks.
A tired double triode (regulating of HV, mostly E82CC) is also possible.

I have no 545 in my collection, but the 545A, they are strong relatives.
531A, 533A and a couple of 535A is also at home here.
They are all restorated.

greetings
Martin
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Old 4th Jan 2016, 10:51 pm   #16
ljdavek
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Smile Re: Tektronix 545 Oscilloscope fault

Hi all,
and happy new year!! i'm still alive so that's good iv not had chance to look in the scope yes just getting Christmas out of the way and got a house of 5 here so but crazy and we might be moving back to Ten Mile Bank by 1st of Feb . soo got to pack as well... but the scope is sitting on the floor of spear room at moment so i can go test in the next day or 2.... i do have a Mullard high speed valve tester i got of the same guy but it is missing the reject card for set up....

oh will and avo do for voltage testings?

will keep you posted!!!

Thanks for all the info so far and yes il get some pics of it on ok

Dave.
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Old 5th Jan 2016, 10:42 am   #17
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Default Re: Tektronix 545 Oscilloscope fault

Yes, the Avo will do for voltage testing. Don't start checking valves until we've figured out what the fault is, and definitely don't start changing capacitors whatever you do. There are dozens, if not hundreds, of them in this machine, and in my experience they're very high quality. I have two Tek scopes of this vintage (a 535A and a 549) and they're both working well with all their original 'Dubilier' capacitors. I hear that the Tek scopes built in the US use 'bumble bee' capacitors which are notorious for going wrong, but most of the ones in the UK were built at the Guernsey plant and used different components which don't fail in the same way.

Chris
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Old 7th Jan 2016, 6:33 pm   #18
6AL5W-Martin
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Default Re: Tektronix 545 Oscilloscope fault

Interesting.

I have not found differents from Guernsey made Tek to others except the manufacturings of the valves and the printing of the front plate.

greetings
Martin
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Old 14th Nov 2017, 8:47 pm   #19
ljdavek
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Default Tektronix 545 oscilloscope fault.(revisiting)

Hi all I'm revising this because Iv kind of got some life out of it now here is the original post I put up in 2015....



Tektronix 545 Oscilloscope fault
Hi all,
hope your all ok, I have this Tektronix 545 Oscilloscope that a friend gave me,

so i did try it out and did get a very bright green dot appear so seemed all good but then sort of vanished!! now i just get a sort of green smudge on the screen that moves about a bit when adjusting some of the knobs. I'm guessing some caps need changing could someone tell me where to start as there is a lot of stuff in this scope..

So I tryed it again today in a new house and to my suprise it almost works!! but I can't seem to get any signal on the screen when I put a test signal from my generator on any part of it need help maybe setting it up? If someone can tell me how? Here some photos....

Thanks

Dave.
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Old 14th Nov 2017, 9:21 pm   #20
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Default Re: Tektronix 545 Oscilloscope fault

I think your scope is working, but we need to check how some of the controls are set and where your signal is connected to.

First of all, set the 'TRIGGERING MODE' (red knob, top right) to 'AUTOMATIC' and the 'TRIGGER SLOPE' (black knob, top right) to 'INT +'.

Connect your input signal (about 200-400mV pk-pk should be OK) to the 'A' input on the type D plugin unit and select 'A DC' on the input selector knob. The type D is a differential amplifier and may be a bit finicky to work with. Set 'MILLIVOLTS/CM' to 100 and the 'MV/CM MULTIPLER' to 1. The trace may jump off the screen when you do this.

Set 'VERTICAL POSITION' to about the middle of its travel (probably with the white dot at the top) and then use the 'PREAMP BALANCE' control to bring the trace to roughly the middle of the screen. The little neon lamps above the screen show you whether the trace is off the top or off the bottom, which is really helpful.

At this point you should be able to see your signal. If there's no sweep at all, turn the TRIGGERING MODE to 'AC SLOW', set TRIGGER LEVEL to the centre (pointing straight up) and play with the STABILITY control - there should be a 'sweet spot', between no trace and a free-running trace, where proper triggering is achieved. You may have to adjust the timebase (TIME/CM control and its multiplier below) to suit your signal.

These scopes are powerful but can be fairly complex to drive, especially the early models like this. Download the manual from here:
http://w140.com/tekwiki/wiki/545
(the first link under the picture) and read the basic setup instructions. There are a number of controls you need to get to grips with which modern scopes just don't have: the STABILITY control for the timebase, and the BALANCE control for the Y amplifier, for example.

Good luck - it's worth persevering!
Chris
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