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Old 10th Apr 2011, 10:42 am   #61
Red to black
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Default Re: TEK scope excitement dashed

You can't give up now OTT!, so near, you only have a couple of connections to try out.
Nothing ventured, nothing gained as they say, or he who dares, wins (so they tell me!).

I know I cannot really help practically, but as another poster has just said

Quote:
The worst that can happen if all is connected correctly is too dim, poor focus or not enough deflection.
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Old 10th Apr 2011, 1:24 pm   #62
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Default Re: TEK scope excitement- 2205 tube.

Quote:
Originally Posted by oldticktock View Post

The 2215 apparently would not work either, see above from post #37

As I mentioned before I'm very confused by all of this too, so not really wanting to spend another day with my head stuck up this scope rear or fry a perfectly good CRT, or destroy what remains of the TEK which could be used for spares, I shall retire from the proceedings whilst the day is young.

Although i'm very grateful for all the advice, it is starting to confuse oldticktock as I seem to be going back and forth.

Cheers chaps, I really do appreciate the input but my skills in test equipment repair are non existent and I really don't want to start frustrating you all any further.

Chris
Come on Chris, have a little faith.
Nothing bad is going to happen to the CRT unless you drop it.
If your not prepared to spend half an hour swapping a few wires around, then that is frustrating.
Do you want to be able to say "Yes, I can master this", or "I gave up at the final hurdle, despite a lot of encouragement and assistance?"
Would you give up if it were a Television set you were restoring?
Regards,
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Old 11th Apr 2011, 12:20 pm   #63
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Default Re: TEK scope excitement dashed

Hi chaps,

So as to not let anyone down and for those like me who's curiosity just needed to see what would happen, here we go. The trace is there, focus & Intensity work, however the scan only seems to fill half of the screen.

The vertical position control has no effect

The horizontal position control can only move the scan to the far left if you rotate the control right! leaving about 1cm visible, if move to the control to the left it scrunches up a bit leaving a gap iof 1cm on the scan on the left wit a pronounced dot on the other end of the line

Only one of the beams Chan 1 is present, Chan 2 is not. When hooked up to a signal and chan 1 nothing is picked up just the flat line.

Chris
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Old 11th Apr 2011, 12:46 pm   #64
Brian R Pateman
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Default Re: TEK scope excitement dashed

Excellent Chris!

You have made progress.

Now, bearing in mind that the 'scope had suffered in transit sufficiently to smash the tube, check to see if there's any other damage. Plug/socket connections, cracked tracks etc.
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Old 11th Apr 2011, 1:07 pm   #65
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Default Re: TEK scope excitement dashed

An initial look over and the board looks intact if there are any cracks they are hairline as I cannot see any. I will check and double check using mag lamp.

What I did find and whether it is related I don't yet know. I found a thin brass screw on the bench. It appears to be out of a core of a capacitor there are two, one has its brass screw the other is missing I presume the one I found.

The capacitor in question is C243, it's partner which has it's screw is C242.

I've attached a picture showing the caps, and the 3rd hand holding the brass screw that fell out. I've looked on the schematic and cannot locate it, possibly it's on another sheet.

Chris

EDIT:
Found C243 it's in the Vertical Output amplifier and is marked as HF Comp (pic of section added) not sure what the missing screws effect would be but perhaps why I have no vertical movement on the adjustment?

Also added a map of the current wiring to the base of the new CRT
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Old 11th Apr 2011, 1:39 pm   #66
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Default Re: TEK scope excitement dashed

Hi Chris. It's quite likely you will have to reverse the connections to the 'x' plates to make the horizontal control work the right way round. Think about a stereo amp with left and right speakers reversed and the balance control seems to work the wrong way round. Same thing with the 'x' control. You may have to do the same thing with the 'y' plates.

Check the controls on the front of the scope. Sometimes the 'y' input has an AC-0-DC switch position. If the switch is at 0 it effectively earths the input so you won't get any response. If so, switch it to 'AC' and try again.

Put the screw in and try!! I doubt it will stop the verticals from working but you never know. You can't do any harm by twiddling it and fine adjustment can be done when the rest is working.

You can check with a meter to see if you get a dc variation on the x and y plates as the appropriate controls are rotated. The drives for a scope CRT are really not that complicated although I agree that some of the signal and digital processing can be daunting. Hopefully this will just be a drive/connection problem.


SB
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Old 11th Apr 2011, 1:46 pm   #67
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Default Re: TEK scope excitement dashed

Hi Rich,

Thanks for that info regarding the X plates and hoz control, makes sense when you put it like that. I tried the AC-GND-DC combo and it's unresponsive I tried all sorts of other settings to see if anything could be coaxed out.

Chris
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Old 11th Apr 2011, 1:59 pm   #68
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Default Re: TEK scope excitement dashed

Quote:
Originally Posted by oldticktock View Post
Only one of the beams Chan 1 is present, Chan 2 is not. When hooked up to a signal and chan 1 nothing is picked up just the flat line.

Chris
Almost all "dual" scopes I have used have really only one beam. the Y axis is either "chopped" much higher frequency than X scan, or at higher X timebase the Y squarewave is 1/2 frequency of timebase.

The Y1 and Y2 inputs Axis Shift knobs thus vary DC offset of the + and - part of the "alternate" or "chopping" squarewave.

So no Vertical axis movement and and only one trace can be due to fault in the same circuit, the Y drive. Some Scopes put signal at one terminal and the Y axis/Chop DC at the other plate, others use the Y amp for signal and position.


The brass screw is possibly one "plate" of capacitor and only affects high frequencies. Not the DC offset.

check the Ya and Yb connections on tube using multimeter. If they don't change with Y-Axis or with variable DC ( say PSU and 30V range and DC mode on attenuator/input), then problem is in Y driver amp.

Last edited by neon indicator; 11th Apr 2011 at 2:06 pm.
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Old 11th Apr 2011, 2:51 pm   #69
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Default Re: TEK scope excitement dashed

Actually glancing at Schematic the Y plates are driven by a differential amplifier. So Y1, Y2 inputs and Y1, Y2 axis shift and chop/alt/Y1/Y2 switching is all one shared Y axis amp driving the plates differentially.
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Old 11th Apr 2011, 4:12 pm   #70
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Default Re: TEK scope excitement dashed

I',m glad you have persevered. It really should not be a difficult task, as it is a very simple tube.
Rob, Glowing Anode has I suspect mis-read pins 6 and 8, and if you have followed him, then that is why your X deflection is only half width. Interchange those pin connections. Connect new pin 12, a1/3/ips to wire for old p9, a3. Remove leads to old p8 a1 and p10 ips.
I attach a summary of the pin connections for the Tek2205, the D14-250 as Telequip D1010, and 56825 for OS300.
MikeR seems concerned about all those grids. The cathode produces the electrons, the flow is controlled by the Grid /g1, varied to control intensity.This assembly appears as a small cylinder at the start of the electrode structure. The electron beam is formed by A1/g2 (a disc, or sometimes a very short cylinder), focused by A2/g3 (a long cylinder), accelerated by A3/g4 (a cylinder or several discs), passes through the Y plates, then the Inter Plate Shield ips /g5, a disc (used for geometry correction), then the X plates and off to the screen. Have a good look at the smashed tube, and you will easily be able to recognise the various elements as it appears you have the beam forming and deflection plates assembly virtually unharmed.
If the tube has Post Deflection Acceleration, pda or a4 /g6 and your has not, then there are various additional elements which can include a fine mesh, coatings on the glass wall of the bell etc.
I have used the British descriptions for the elements of the tube as anodes. Tek describes all beam forming elements as grids, but some other US use the British. German and Philips use both. I have marked on the attached connection summary the alternative names for the elements. I add that US and Philips terms D1,D2 = X deflection plates, and D3, D4 = Y plates. Never mind whether 1 or 2. If the trace is wrong way round or inverted, interchange the connections. Many makers combine the a1,a3 and ips elements onto a single pin connection, and that has happened here it seems.
I have tried to summarise the physical shape and purpose of the various beam forming elements, as it is not normally difficult to identify the connections to the various elements by inspection, and confirm duplicated pin connections (often marked IC on data sheets) with an ohm-meter. They are usually the a1,a3,ips structure.

Operating voltages are typically k=0, g=-50, a1=a3 accelerator=ips at 2Kv, a2 focus at varying around 200v, deflection plates same as a3, hence the astigmatism control to vary the a3 around the deflection plates mean potential. On some tubes, the ips is kept separate, and a geometry control fitted to vary the potential around a3 to give a squarer scan, though is is normally now done by tighter tube manufacturing tolerances. As the deflection plates have to be near ground or HT, in practice the cathode and grid are at 1 to 2kv negative. Never poke your meter onto the grid, as the current will make it sufficiently positive to burn the tube out.
Your other problems with a single trace are nothing to do with the tube. Look at the Y2 amplifier circuits and switches. Bill m0wpn
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Old 11th Apr 2011, 5:00 pm   #71
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Default Re: TEK scope excitement dashed

Wiring amendments made, now I have a better line trace. It can be moved left to right but does not fill the entire screen.

I think as some have suggested already more damage must have been caused when the tube broke, as It will not see a signal source as well as chan2 missing

Chris
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Old 11th Apr 2011, 5:11 pm   #72
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Default Re: TEK scope excitement dashed

Quote:
Originally Posted by WME_bill View Post
MikeR seems concerned about all those grids. The cathode produces the electrons, the flow is controlled by the . Bill m0wpn

Not really Bill. My concern is that all of these internal connections could short circuit some of the TEK circuitry such as astig and geometry or pull some circuitry down to earth.

I rpeat that I can see how the TEK tube would be a viable replacment for an OS300 but the OS300 is not a replacment for the TEK. Some functionality will be lostat best.

Mike
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Old 11th Apr 2011, 5:32 pm   #73
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Default Re: TEK scope excitement dashed

I totally respect your comments, and you may well be right.
This was a scrap scope, about to go the way of all fish.
Full credit to Chris for having the determination to at least get a trace (first light) out of this scope, and will certainly have a better understanding of and confidence around crt circuits.
Bill, well done for getting the right pin numbers, I must get my eyes done.
I'm sure there's a bit of gain to spare if the deflection is not as sensitive.
Keep going Chris, we're all very proud of you.
Rob.
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Old 11th Apr 2011, 5:59 pm   #74
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Default Re: TEK scope excitement dashed

Yes well done OTT!,

Even if you don't get it working correctly, at least you have tried!, and possibly learnt something, well done once again.

Just a few more niggles to sort out now, you are nearly there.

Cheers,
Baz
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Old 11th Apr 2011, 9:23 pm   #75
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Default Re: TEK scope excitement dashed

Looking good, probably now just need to fix Y amp.
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Old 11th Apr 2011, 9:37 pm   #76
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Default Re: TEK scope excitement dashed

Therein lies the problem, if this were a 405 TV or if it had components I could see or even understand (chips what!! let alone those three legged beasties) without going boss eyed I might have a fighting chance. I probably should do a bit of reading if I intend to go further. Bit of a technological leap from my comfort zone and where I am at the moment.

Chris
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Old 12th Apr 2011, 8:26 am   #77
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Default Re: TEK scope excitement dashed

1st check the Y amp board has all supply volts and a 0V/Ground return.

Start at input with one channel only selected and a 5V or 12V PSU or 9V battery as source.

DC coupling.

click on attenuator between 1v, 2v and 5v per cm ranges and trace the Y signal from Attenuator to Y amp and through Y amp from input.
When you get to a stage where the input changes and output doesn't you found the broken 3 leg beast.

Since the Y AMP is DC coupled and the Attenuator or Y-Axis will vary DC volts it's easier to trace from input and find faulty part than a 405 Line IF strip. Only a Multimeter needed!

I'd suspect one or both output stages as there may have been a short between the outputs if it was turned on with damaged tube
Q238, Q239 is push pull and Q237 + another.
A pair of push pull amps driving differentially. If Y-Axis knob moved the amount Q239 collector goes up (or down) should be equalled by Q237 going down (or up)

Last edited by neon indicator; 12th Apr 2011 at 8:32 am.
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Old 12th Apr 2011, 10:42 am   #78
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Default Re: TEK scope excitement dashed

I've not joined in this discussion yet as someone has already mentioned the Yahoo!!!! group, "tekscopes" which is where all the ex-Tek engineers seem to hang out...

What might be worth mentioning is that there is a great supplier of Tek spares based in Europe (on Rhodes of all places), called QService - http://www.qservice.tv/vpasp/default.asp

No connection with them other than having used them to get some weird parts in the past, including hybrid input attenuators for my Tek 2465A etc. Nice bloke to deal with - very helpful & fast.

Should mention also that if you don't see something listed, just email & ask - he has a bunch of other stuff around too... goes by the name of "Dinos" ISTR...

Cheers
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Old 12th Apr 2011, 12:20 pm   #79
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Default Re: TEK scope excitement dashed

Hi Chaps,

New morning, fresh start I sat and stared at the PCB and stared at the PCB, then under the mag lamp I noticed a 2 strip black ribbon lead looked a bit flimsy, give it a poke I thought , plop it popped off must having been hanging on by a thread.

Hmmmm, soldered a couple of more robust wires then soldered the old ends to those. Switched on and nothing no trace I thought then numpty boy pressed beam find and it was right off screen, yipee vertical position now works again.

So I have hoz & vertical, I thought lets connect to the calibrate point see what I get, then I connected to a speaker and got a weird trace, then a LOPT for the ring. It's talking to me, I still think its unwell as the LOPT ring is not nicely formed and I know the LPOT is good as it gives a good ring and Trace on the Telequipment scope.

Still glass half full and all that a better place than it was a week ago.

Chris
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Old 12th Apr 2011, 12:31 pm   #80
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Default Re: TEK scope excitement dashed

Tidied up the ring trace a bit still looks not quite right
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