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TEKTRONIX 465B BrownOut

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sesosoft

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I was using my TekTronics 465B to repair another generic oscilloscope then accidentally I touched a contact point sticking out upwards from the generic scope’s board. I must have touched a very high voltage point because I did see a very small spark at the moment of contact, within a couple of minutes the waveform of my TekTronix slowly began to fade away. Now the screen is half illuminated, (diffusely illuminated) from the right side to the center and to the left side is a bit darker (sort of like a half moon effect). Only the intensity control seems to have any effect at all on the display, but it doesn’t do much other than make the screen just a tad brighter.
Does anyone have any idea at all what I must have ruined on this old trusted friend. I am so pissed I have hand this scope since 1989 and it had been working great since then till I messed it up.
Please help. Thank you very much for your help.
 
I have an old and trusted 465, too - I use it to double-check my digital scope (which sometimes lies to me).

My guess is your horizontal plate driver's shot. The horizontal deflection circuit is on the bottom board in the scope. Q1282, Q1286, Q1262, and Q1266 do the heavy lifting, they form a pair of bipolar push-pull amps, and are touchy because they deal with high voltage (+100V to -8V) and high frequency to drive the plates on the CRT.
 
From your description, it sounds as if something is driving the beam off-screen to the right. The horizontal deflection amp may be saturated one way or the other for some reason. If turning the intensity all the way down doesn't darken the screen, then there may be other problems. What happens when you press the Beam Finder? And what happens if you engage X-Y mode? Remember to reset all the position controls to center.

For trouble-shooting, you'll need a service manual for your model. I think there are two for the 465B, depending on the serial number. First order of business would be to check the internal fuses and verify that all the DC power supply rails are within spec.
 
Also check TP1518 and TP1536 to see if you still have +110V and +55V, respectively. Those are the voltages used by the deflection circuits.
 
TekTronix 465B

Thank you very much fellows for your replies. I appreciate it very much. This weekend I had planned on opening up this my old trusted 465B scope (again) and take a look inside at the points suggested here by Duffy. I had already opened it and verified that all the fuses where good and it was clean and nothing smelled burn and all that was fine, I just had up until this point NO CLUE where to start looking. And in response to ModemHead, Nothing happens when I push the Beam Finder the beam does not appear.
But now you guys are simply going to scratch your heads. I bought another used Tektronix oscilloscope (from a friend for $300 dollars) a 2445 150 Mhz. with four channels. He had had it in his garage for god knows how long and only remember after I told him the problem I was having with my 465B; When we gave it the smoke test at work the trace promptly came up, it looked crisp and within focus, all the buttons seemed to work properly, brought it home cleaned it up and sat there waiting for this weekend to try it out. It worked just fine for about 20 minutes then the trace completely went out and is nowhere to be found. When I push the BeamFinder nothing happens. Although all the other little LED are on and the screen illumination works. There is no trace. Nothing. So another $300 dollars down the drain. It seemed such a good deal.
Any ideas on what might have gone wrong with this one. This time there were NO mistakes from my part. I was only using a 15 volts power supply through the 10pf 1.5 Mega Ohm prove looking at the collector output of a 2N3904 transistor when the trace decided to quit. No shorts, no smell, no pops, no sound. Just plain darkness from the CRT.
Thank you fellows.
 
TEKTRONIX 2445 4Chnl 150 Mhz Scope

I recently bought a used TekTronix 2445 150 Mhz scope from a “friend”; he had had this scope in his garage for god knows how long. When we first gave this puppy the smoke test, it worked fine! The trace came on crisp and within focus, all the buttons and dials worked fine, no smoke came out and nothing smelled either. This weekend as I tried it out, connected it to a two 2N3904-transistor flip-flop circuit, on a 15 volts power supply it; it worked fine for about 20 minutes then w/o any warning, complaints or any kind of fuzz at all the trace on all channels simply went off. The “Beam Finder” finds nothing now. All of the LED still work exactly on the settings I left them. The screen illumination works just fine too. But there is no trace at all. No burnt smell, no noise, no rattles. But it still has power. The power light is on along with all of the other LEDS.
Help. 
Thank you very much.
 
I was using my TekTronics 465B to repair another generic oscilloscope then accidentally I touched a contact point sticking out upwards from the generic scope’s board. I must have touched a very high voltage point because I did see a very small spark at the moment of contact, within a couple of minutes the waveform of my TekTronix slowly began to fade away. Now the screen is half illuminated, (diffusely illuminated) from the right side to the center and to the left side is a bit darker (sort of like a half moon effect). Only the intensity control seems to have any effect at all on the display, but it doesn’t do much other than make the screen just a tad brighter.
Does anyone have any idea at all what I must have ruined on this old trusted friend. I am so pissed I have hand this scope since 1989 and it had been working great since then till I messed it up.
Please help. Thank you very much for your help.
 
I wish I had a friend like that with a Tek CRO in his garage.
Can I suggest you get the manuals that ALWAYS come with top shelf gear like a Tek. Then get stuck into it. Maybe EBAMAN has a manual.
Good luck.
 
I can understand your 'pissed off-ness'. Like I said with your other Tek, get the book first then get stuck into it.
I have an old 564 WITH MANUALS. Wouldnt dream of fiddling with it without them. In my case, the tunnel diodes in the timebase are virtually unobtainable, and to keep it going it has to be re-engineered with modern available semiconductors. Couldnt begin to redesign it without the manuals to know whats there.
The thing is full of germanium transistors, RCA micro valves, tunnel diodes, high power triodes and pentodes; most of which arent available. It will go to heaven if the cro tube fails.
 
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There is a very good chance that both of your scopes can be repaired. It will take some effort and learning on your part, but there is a wealth of resources on the internet for repairing old Tek scopes.

Get the service manual for your models, if you don't already have it. Two possible sources: KO4BB and BAMA. If you find the free versions to be incomplete or hard to read, Artek Media has better copies with higher resolution and bookmarked table-of-contents for a small price.

Read the Tektronix manual Troubleshooting Your Oscilloscope. This was written by the folks who designed your scope. They know what they're talking about. More so than me.

Join the Tekscopes Yahoo Group. People that collect and repair vintage Tek hang out there.

This bears repeating: first order of business on either scope is to check power supplies and fuses. IIRC, the 465B has at least three PCB-mounted ones in the corner near the power transformer. If you find a blown fuse, don't just replace the fuse, check those rails with an ohm-meter, you may find a shorted tantalum capacitor, or a shorted semiconductor. Then check all power supply rails for correct DC level and lack of ripple. You can use a decent DMM for that. The service manual will tell you exactly how close each supply should be to its labeled value. Re-check those test points with the DMM set for AC volts. A scope is the better tool here, but if you get a significant reading on the DMM you may have a bad electrolytic filter cap.

On the 465: if your tube lights up, this is good, it means you have high voltage and a beam somewhere. From your description, it's off to the side, which indicates a horizontal deflection fault, as noted earlier. X-Y mode disables the sweep, so that will tell you whether to go for the sweep generator or the horizontal deflection amp. The amp seems more likely, and the outputs, as duffy said, are good suspects. Oh, and the transistors are all socketed on the 465B, so give everything a good wiggle. You may get lucky.

If you decide to dive in, don't forget to be mindful of the high voltages present in some areas. This includes not only the obvious CRT circuits but the deflection finals as well. It can destroy test equipment, and it can destroy you too!
 
Update to this tale of two TekTronix.

TekTronix 465B

After so much fear and indecision to commit what seemed to me “sacrilege” to open my 465B up and see what if I could fix it, I opened it and fixed something. I will make this tale short and techincal. I did found out there was no +15v regulated power supply output. By looking at the service manual and following the 15v power supply isolation procedure (page 281 service manual) and then disconnecting some components, transistors, diodes and capacitors, one at time and checking out the voltages as per the manual. I traced the source of the problem to Q4403 and C4331 on the +15v power supply, they were loading down the voltage output of U4411 and hence producing no +15v output. The problem was C4331 was shorted and Q4403 was open, once removed and replaced the power came up and the scope worked.
The problem the scope has now is that the trace is very wiggly, it seems to have a bad case of the shakes. I can barely get the trace hold control to actually hold the trace in place, but is not crisp and straight as before and is wiggly, it is also distorted at the top and bottom, but the biggest problem is all the shaking. At this point I have no clue what else I messed up the first time. I can post a small video here on you-tube is this would help you fellows help me out.
Hilfe!

TekTronix 2445

I traced the problem to U1830 the voltage doubler (block or red box “sealed” component) on the high voltage module. It might have a blown diode in it. To figure this out I followed the blown fuse connections, till I got to the transformer that drives U1830. By unsoldering the transformer connections to U1830 the fuse did not blow up anymore, so thus I isolated the problem to the voltage doubler. There are two secondaries from T1970 now I have to resolder one a time either set of them and that would tell me exactly what part of the U1830 circuit is bad once this is done I will try to FIX, yes FIX this “sealed” component by melting away the guey tar that is sealing it. It is probably just one bad diode that blew up on this. I will keep everyone posted on this,

thank you y'all
 
ModemHead thank you very much for your great advice, except for two suggestions here in your reply that I have not done yet but will do immediately, I have actually followed most of the rest, I did find the problem almost exactly as you descrive it; a shorted tantalum 47mF capacitor and an open transistor. I suspect that some of problems I am seeing now with a very shaky trace may be attributed to AC ripple and/or noise, because YES those old caps in the voltage doubler have leaked some, there was a lot of black residues I cleaned off from around them on this section of the board. I may actually replace them all with new ones, if I can find a good replacement for them. I will follow the rest of your recomendations here almost to the letter to measure the ripple and hopefully what would lead me to pin point the source of the trace shakes. Thank very much again
 
Great! Sounds like you're making good progress. And the shakey trace could easily be a problem with power supply ripple. The black residue around the HV areas is pretty normal since dust is electrostatically attracted to those areas, that probably doesn't indicate any particular problem.

By the way, I don't think digging apart an HV multiplier and then re-potting it is an easy job...

Keep up the good work.
 
Man, I'm so glad I found this thread.
Hi everyone,
I have the same problem , (the voltage multiplier out of order). I managed to identify the problem by disconecting the two wires from T1970 to U1830. The problem comes from the "lower" part of the U1830, the section that generates the -900V and -1900V. Before replacing the HV module I would like to open it up and see if anything is repairable.
Any success in removing the "guey tar" Sesoft?

thanks.
 
Man, I'm so glad I found this thread.
Hi everyone,
I have the same problem , (the voltage multiplier out of order). I managed to identify the problem by disconecting the two wires from T1970 to U1830. The problem comes from the "lower" part of the U1830, the section that generates the -900V and -1900V. Before replacing the HV module I would like to open it up and see if anything is repairable.
Any success in removing the "guey tar" Sesoft?

thanks.

Hi automihai. Welcome to ETO! :)

It's generally best to start your own thread, rather than taking over someone else's. You can provide a link to this thread in your own, but usually you should not ask your question in an existing thread. You're new here, so I imagine you're still very new to the setup. Just a friendly reminder to start your own thread whenever possible ;)

Best wishes,
Matt
 
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