Tektronix 2465B oscilloscope teardown

[med6753]

Wow, that's a hell of a mess. Obviously the seller did drop it, or it fell off a bench. I'm sure he knows exactly what happen and doesn't want to admit it. And it's hard to say if there's other damage until after you install a replacement CRT.

But it is neat to see Tek's innovative and at the time leading edge process that combined a ceramic bell of the CRT with the glass gun and faceplate. As far as I know no else attempted that. But I did read somewhere that Tek shared some of their CRT technology with Sony which directly influenced the design of the Trinitron CRT.

[David Hess]

But it is neat to see Tek's innovative and at the time leading edge process that combined a ceramic bell of the CRT with the glass gun and faceplate. As far as I know no else attempted that. But I did read somewhere that Tek shared some of their CRT technology with Sony which directly influenced the design of the Trinitron CRT.

Tektronix started using ceramic CRT envelopes in 1962 with the 561A and this also allowed marking the graticule on the inside removing parallax error.

[BravoV]

What a bummer  , really sorry to hear that cheeseit. 

Please, once you have the replacement tube, share your journey here please, that will be really interesting.

PS : The broken tube, have you dump it yet ? I really love to own it if you're going to toast it, as the gun and metal parts inside looks artistic, at least to my eyes. I will pay for the shipping cost.

[tggzzz]

... the gun and metal parts inside looks artistic, at least to my eyes.

And mine.

I was lucky to have access to a glass bandsaw. If I hadn't I would have had to experiment with heated nichrome wires.

[cheeseit]

Been there, done that, ended up with: https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/

I had seen that before and it was the second thing that came to mind after pulling only the top half out of the scope, right after "#&!$ hell". It looks awesome!

I've been emailing with the seller and he insists that it was not dropped and he does sound sincere. He called it his dear scope and talks about how he would hate to see it trashed and that he really hope I will try to find a replacement tube. I don't know, seems implausible that it would snap in two without an external force so maybe it happened in transit and something else is arcing too.. Whatever it is, it needs a new tube now so time will tell if it holds any other surprises.

Such a tube is a technical marvel IMHO and deserves to be displayed, though SWMBO had the ".. yes, very cool.."-look on her face when I showed her.

PS : The broken tube, have you dump it yet ? I really love to own it if you're going to toast it, as the gun and metal parts inside looks artistic, at least to my eyes. I will pay for the shipping cost.

I feel the same about its looks so I hope you can find another tube somewhere. Any ideas for making something of the envelope funnel? And sure, I will update once I make some progress.

----

I didn't realize that the tube I linked to was on sale and that the sale ended a few hours ago. So, having spent some time searching for scopes and tubes that was reasonably priced I wrote the seller asking if there was a chance that I could get the 12% off sale price. There was and the tube will be on its way in a couple of days. They say it is an 8 on a scale from 0 (dead) to 10 (brand new) so I figured that it was worth it, especially considering the 30-day warranty. The seller even gave me a 15% discount instead.
Now I just need to decide whether to try the tube in the scope in its current condition, or order new caps and recap it first. I'm leaning towards testing it before recapping, in case something else is damaged.

[cheeseit]

My new tube has finally arrived and is still in one piece. Qservice had packeged it real good using loads of bubble wrap, foam and tape. It came in a cardboard box with British American Tobacco Group logos. Wonder if that triggered an inspection or x-raying along the way..


Date code is from week 15 in 1993 and it looks good, with no soot but that could of course just have been cleaned off. I trust the seller though and hope it is as good as the service he provided.


I have decided to just recap it before installing the tube as it seemed likely that the only problem was the broken tube. I ordered caps from Mouser late last week which is scheduled to arrive tomorrow so hopefully this lovely scope will be up and running soon once time permits. Should be later this week or the next.

This is my first time replacing a CRT but I'm guessing that I will likely have to do some or all of the adjustments outlined in the "CRT Adjustments"-section of the SM, right?


Edit: this is the old tube, disregard the light specs and what looks like (and is) a brush stroke. That Lichtenberg-looking burn, does that perhaps indicate that the tube was powered when it had its catastrophic failure?

[David Hess]

This is my first time replacing a CRT but I'm guessing that I will likely have to do some or all of the adjustments outlined in the "CRT Adjustments"-section of the SM, right?

Yes and the horizontal and vertical deflection will probably need to be adjusted as well.  The transient response may be affected but if you do not have a suitable signal source, leave it alone.

Edit: this is the old tube, disregard the light specs and what looks like (and is) a brush stroke. That Lichtenberg-looking burn, does that perhaps indicate that the tube was powered when it had its catastrophic failure?

That is what happens when debris gets lose inside the CRT envelope (no surprise here) and contacts the phosphor which is very delicate.  It is a bad idea to move or store CRTs face down.

[BravoV]

cheeseit, readying pop corn to watch your journey, please share it here along with photos, thanks in advance.   

[Fateh Singh]

I have been reading the messages on this topic and find them enlightening.
On my own machine -2465B- I have  changed the capacitors as already advised by many experts here, and has the supply
voltages are under specs. For a few days , I was confounded by  very high voltages on all lines, when PSU was powered outside
the machine. Then somewhere, I read that the supplies have to be loaded to be tested. On loading the supplies settled OK.
Now, the machine has the following problems-  It shows   Fail Test 05 -44.  Presumeably,  the DAC312 and the Comparator 311 on A5 has something wrong.
The 311- pin 7 output shows fluctuating 0.8V when the test is looping.  Grid bias is active. Focus is acive. Intensity pot has no effect. Beam find brings the beam into a small rectangle in the screen center. Otherwise the beam is off screen with only spots on screen. I will continue the search for faults, because i want this wonderous machine to help me in my many projects.
Kindly help with your questions and suggestions. I would like to post a small video of what the screen looks like, but just now, i dont know how.
Many thanks .

[med6753]

Now, the machine has the following problems-  It shows   Fail Test 05 -44.  Presumeably,  the DAC312 and the Comparator 311 on A5 has something wrong.

If this fail occurred after you replaced the caps and reassembled the scope go back and check the ribbon cables that plug on the underside of the top plate. It is very easy to plug them one pin off or they aren't fully seated. We've all done it and it causes those trigger level fails.

[Fateh Singh]

The ribbon cable is on A5 and it is going to many front panel switches. Did you mean this? It seems very secure. I have not touched it.
I have another scope, and will look into the signals from Comp311, and will revert. Meanwhile , the status quo. Error test 05  44.

[Bryan]

Just as a double cre you positive the voltages are in spec and you have checked for ripple using another scope. Can do funny things when not in spec.

[Fateh Singh]

I am checking with  TDS7104- dig. scope- using it first time. The trace appears a bit noisy- unlike smooth lines in analog scopes.
Supplies + _5V, +_15V appear OK. 42V and 87V  not seen yet.
On A5 board  Test pin wave forms  1 , 2 , 4  appear OK.  no. 3 on U2540 hex inverter pin 10 , is not there ( remains high ) pin 11 is remains low.
So this chip is innocent.
The comparator 311, appears to give out on pin 7-  some pulses longer than others.Why?

[Bryan]

What do you mean the 42v and 87v are not seen?. Are the voltages not present or you haven't measured.

[Fateh Singh]

Mr Bryan,  I have checked the 87V and 42V supplies with scope. They look OK. DMM measures only 15 mv ripple.
On checking the high voltage A9 card- I find an anamoly. The sinewave oscillation  on Pin7 ,T1970- is not a steady amplitude
+_150V AC.  Its amplitude is modulated- the oscillation builds up and dies down.Each cycle is 5-6 waves. The behavior is the same at  pins 5 and 6.
Because the oscillator is under feedback control with U1956, trying to stabilise -1900V- the IC pin7 has the same modulation at low amplitude.
R1973 is listed as 16K, but actually it was 120K. The layout seems different here, and i am trying to see if any C or R is open /short/out of specs.
My suspicion is on U1956- dual op amp. Its supplies are ok.    -300V supply from doubler fed by pin 7 T1970 is OK- possibly due to filtering
and low load. But this behavior from pin7 must be doing funny things to Control grid voltage and the -1900 V cathode bias.
Thanks for your interest in my woes.

[Bryan]

Fateh:  Do you have the comprehensive service manual for the scope. Sounds like there is some issues with the scope and the A9 board is definitely a area that I am not familiar with. I can send you a copy if you do not have one. You may want to join the Yahoo group Tekscopes. This is where all the experts in teak scopes hang out, if they can't help no one can<g> Takes a couple days to join as the memberships are moderated.

https://groups.yahoo.com/neo/groups/TekScopes/info

[Fateh Singh]

Bryan, I have one downloaded copy with me- and I have all circuit schematics in A3 and A2 sizes.
I am reasonably good at trouble shooting electronic equipment. It is my hobby and my profession now.
We are designing an EV motor and and Inverter. Stuck with the inverter, that requires 4 isolated 20 V /0.5A
supplies. Hence the requirement of good quality Oscilloscopes.
Please send your copy of the service manual by mail-  fs_monder@yahoo.com.

Many thanks.
Fateh

[Bryan]

E-mail sent

[Fateh Singh]

Bryan,

We have got it RIGHT, after much hair splitting. The error message  Fail  Test 05  44   passed after change R2013. I dont know stable or accurate
that is.  The HV control system loop oscillation, went away,  after some prying  about U1956. I tried putting another capacitor across pins 1 and 2 . No change except a little lower modulation frequency.  Possibly, some dry solder point got set right.

Now, all four channel traces are on screen , and they can be moved about. Intensity control OK. Focus OK. Checking calibration can wait.
Replacing electrolytics on A1 card can also wait. It looks like a difficult maneuver just  now. May be NV RAM data transfer to another compatible
chip later on. Breathe easy now.

Thanks everybody here, especially about clearing doubts about DAC functioning.

Fateh

[Bryan]

That is good news that you got it fixed, or at least hope so. One thing I would do as a priority is get the Dallas NVRAM changed sooner than later or risk losing your calibration data. The battery on the chip is probably close to 25-30 years old by now. Lot's of threads on how to replace.

[cheeseit]

It's alive! No more arcing and now with squiggly lines on the tube!


Apart from the missing adjustment everything seems to work as far as I can tell. (?) The image looks a bit more fussy than IRL but it definitely needs adjustment - I assume that it is possible to adjust it to a much sharper image? ATM this is the best I can achieve using the front panel adjustments.

The PS has been recapped and I replaced the single electrolytic and the fuse on the HV-board. Two 15R resistors (R1010 and R1019) on the regulator board were replaced with beefier ones. One measured open and had visible cracks, and the other measured 68K and had tiny scorch marks, both out of circuit.

Handling and installing the tube was a bit scary since this is the most expensive single part I have ever replaced, and of course, because of the fragile glass. The tube also didn't line up to the holes in the shield as well as the old one did. The ground pin was so crooked that it was impossible to use so I had to pull the tube out again and straighten the pin with flat nose pliers. I took great care not to bend it and just hope that I didn't damage the seal but it was unfortunately necessary.

No error codes on boot and the battery is healthy at 3.56V measured on the SRAM supply pins so calibration is safe for the time being. I already bought a new battery and will be replacing the current one. 15592 hours on and 2619 power cycles logged.

I'm not sure how to proceed with the adjustments but will study the relevant parts of the SM and try to figure out what exactly needs to be done and what my options are, given the equipment I have and my limited budget. I will return once I make further progress and/or if (when) I need help. Thanks so far.

[tggzzz]

I'm not sure how to proceed with the adjustments but will study the relevant parts of the SM and try to figure out what exactly needs to be done and what my options are, given the equipment I have and my limited budget.

Congratulations, and that's the right attitude

I presume you replaced those blasted (pun intended) mains filter caps.

[cheeseit]

I was searching for higher bandwidth probes for my 2465B above and ended up buying another (working) 2465B on my local craigslist. The seller obviously didn't really know what he was selling since his reply to me asking for probes was "please explain what probes are and where I can find them". Turned out that it included four P6137 400MHz probes and a single P6105A 100MHz. He also had a manual, quick start guide and a few other bits. He was asking for €270, I courageously (since others were interested too) offered him €148, and got it for €161. Total cost including shipping €180, which to me is a score considering that sold listings on ebay shows the P6137 selling for about €60 a piece plus shipping.

This is what I got:


It looks like it has been stores upright somewhere dirty, or for a very long time. I know that it is trivial to reset but only 3454 hours on and 658 power cycles so I'm hoping that it has just been stored for a long time. Perhaps the inside will give some clues. The three probe instruction sheets I got have revision dates from 1991 to '93 so the scope likely is from this period.
All the probes appear to work. The tube has no burns and is very bright. The 2nd and 4th channel (I think) did show a bit of noise when the scope was cold but that went away after warming up. The readout and traces shimmers a tiny bit randomly from time to time. Otherwise everything appears to work fine but I haven't yet done much testing.




I will open it up tomorrow and see what it looks like inside and what needs to be done but PSU and A5 is likely to need work I would guess. I seem to recall that recapping the PSU has solved issues similar to the shimmer I'm seeing. I'll post once I have opened it and had a look around.

[med6753]

That is one heck of a good score! 

[David Hess]

I got similar deals on a Tektronix 2440 and 7854 which apparently sat in storage for many years and were in excellent condition.  Later I hunted down a front cover for the 2440 so it remains clean and protected.

The 2nd and 4th channel (I think) did show a bit of noise when the scope was cold but that went away after warming up.

Warming up usually results in better performance from aluminum electrolytic capacitors so this might indicate that they are at the end of their useful life.

I am fussy on exactly which 2465 series oscilloscopes had problems with leaky surface mount aluminum electrolytic capacitors but I do not think the early and late ones did but it is still worth checking.

The readout and traces shimmers a tiny bit randomly from time to time. Otherwise everything appears to work fine but I haven't yet done much testing.

Check to see if this is just an artifact of the beam multiplexing needed to display the readout by disabling the readout.  Sometimes the readout will momentarily synchronize with the sweep to produce visible artifacts.