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Old 28th Aug 2017, 6:35 pm   #1
andyjpb
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Default Tektronix 2465 smoke

Hi,

I have a Tek2465 that I bought second hand a few years ago. It's been great!

When I was using it this afternoon I heard a bit of crackling and then, a few seconds later, some black/grey smoke came out of one of the vents at the bottom of the 'scope. The 'scope appeared to be still working but when I saw the smoke I switched it off as quickly as possible.

I left it for a while and then took it apart to see if I could work out what had failed. I couldn't!

I took the 'scope out of the blue chassis. The mainboard at the bottom and the logic board at the side both looked clean and nice. Next, I opened the panel at the top. Underneath were the PSU and the CRT. I didn't take the PSU out but, from what I could see of it, it too looked clean and nice. However, on top of the CRT is a red wire that connects to a large, white, plastic thing and then disappears inside the CRT. This wire and the plastic connector thing were covered in black dust/soot. I (carefully) removed the panel on the side with the -2KV warning and that looked mostly OK but it was quite black and dirty where the previously mentioned red wire entered at the back. The big red thing was clean and nice.


I reassembled the 'scope and plugged it in for a quick test. It booted up fine, appears to work and passed all the diagnostic tests when I ran them.

However, I'm now loathe to use it without working out what's gone wrong and what the implications are of not replacing whichever component has failed.


Can anyone here advise what I should do or if there's anyone in the London area that I can take this too?


Thanks for your help!
@ndy
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Old 28th Aug 2017, 7:03 pm   #2
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Default Re: Tektronix 2465 smoke

It sounds as if an X2 mains suppression cap has gone bang. That's why it still works.
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Old 28th Aug 2017, 7:06 pm   #3
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Default Re: Tektronix 2465 smoke

Thanks for the reply!

Is that something that's easy to replace? Are the implications for not replacing it in a timely fashion?
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Old 28th Aug 2017, 7:46 pm   #4
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Default Re: Tektronix 2465 smoke

Assuming it is what we think it is, usually when it has "gone", it becomes open circuit, however, it may be as well to remove the remains.

It is there as interference suppression, so you really should replace them at some point, but it won't hurt the equipment to continue using it without the part fitted.

As an aside, it is highly likely that there are several (some across the Line and Neutral - "X"- types and some between the mains poles and earth -"Y"- types). I would highly recommend changing them all if one had blown.
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Old 28th Aug 2017, 7:48 pm   #5
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Default Re: Tektronix 2465 smoke

I've recently fixed the boss' 2465 with just those symptoms.

The plastic connector on the CRT is the EHT supply for the post-deflection accelerator. it is at a lot more than 2kV and attracts dust and muck. This is normal and OK.

You are looking for the remains of a Rifa brand capacitor on the power supply board. You have a fair bit of dismantling to get at them. 0.047 uF if I temember.

Many, many bits of equipment have these beasties in them to suppress RF emissions down the mains cable, and they are all getting to the end of their life. It's starting to be a regular occurrence in our lab

There are several photo guides to this job on the 2465on the internet.

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Old 28th Aug 2017, 8:01 pm   #6
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Default Re: Tektronix 2465 smoke

Hi,

Thanks for the great replies!

Now that I'm a bit more confident about what I'm looking for I'll have a read up and see what I can work out.

Thanks again!
I'll let you know when I've worked things out.
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Old 28th Aug 2017, 8:37 pm   #7
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Default Re: Tektronix 2465 smoke

Hi Andy,

If you need a service manual, it can be downloaded here :-

http://www.tek.com/manual/2465a-and-2467-service-manual

(assuming you have the "A" model).

Taking a quick squiz at the circuit, it seems that a lot of the EMC filtering is being done in the IEC socket. However, there are also 2 caps C1018 and C1016 (0.068uF) across the L and N lines, these are in series with small value resistors. In the first instance, I would check out the IEC socket (*Note) and these 2 caps + associated resistors.

(*Note) These can give out loads of smoke, usually from small hole blown in the encapsulation.


In my opinion these 'scopes are the very pinnacle of the art of "analogue 'scoppery" and well worth persevering with.
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Old 28th Aug 2017, 8:44 pm   #8
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Default Re: Tektronix 2465 smoke

This will be the schaffner filter on the IEC inlet. It's about the right age to explode.

Not sure if they out any RIFAs after that to explode as well.

I replaced one in an HP digital scope and it had obliterated everything about 3 inches around it. Took an hour with a tooth brush and IPA to clean it up.
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Old 28th Aug 2017, 10:23 pm   #9
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Default Re: Tektronix 2465 smoke

As noted its almost certain to be the X2 capacitors in the PSU assembly. My three 2465B scopes have all done exactly what you have described complete with the puff of smoke out the vents. (Hopefully it is less likely the insulation on the EHT connector, I have not seen one of those fail..yet)
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Old 29th Aug 2017, 9:15 am   #10
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Default Re: Tektronix 2465 smoke

They all do that, sir. I've got four 24xx scopes and I think they've all released the magic smoke. I'm not sure whether I should confess this, but I haven't done anything about it - just carried on using them. No problems so far, and the scopes are used almost daily in my work.

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Old 29th Aug 2017, 10:32 am   #11
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Default Re: Tektronix 2465 smoke

This is hearsay, but I believe the primary purpose of the mains filter capacitors is to reduce switching noise from the scope power supply getting back onto the mains rather than to reduce incoming noise. I imagine there is so much switching noise in most households that a bit more will go unnoticed. Maybe different in a lab environment.

I must be lucky, my 2465B and 2440 still have the original smoke in them!

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Old 30th Aug 2017, 10:29 am   #12
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Default Re: Tektronix 2465 smoke

Bottled up for that long, it won't be long before the genie escapes!
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Old 30th Aug 2017, 11:32 am   #13
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Default Re: Tektronix 2465 smoke

Quote:
Originally Posted by RogerEvans View Post
I must be lucky, my 2465B and 2440 still have the original smoke in them!
They're like world war two unexploded ordinance. One day you'll get got
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Old 22nd Nov 2020, 3:10 am   #14
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Default Re: Tektronix 2465 smoke

I didn't get around to replacing the capacitors because I wasn't quite sure what I was doing. In the end another RIFA blew and I did some more research.

I took it apart and found out what was wrong. It was the two RIFAs in the mains filtering part of Board A2: C1016 and C1018. I ordered new parts for those and for all the other RIFAs I could see. All the remaining ones were cracked but hadn't failed.

I've had the parts in stock for some time now but I'd been working on and off on a project that I needed the 'scope for so promised myself I'd fit them when I'd got to a couple of milestones with that.

Today was that day.

On the A2 board I replaced:

On the A3 board I replaced:

When I had the 'scope open to spec out which parts I needed I noticed that C1111 on the A3 board was in bad shape. It seemed to have leaked some red and black stuff onto the board. This part was quite hard to come by but my research suggested a 470uF capacitor could do the job even tho' the original was only 250uF.

When I was in there fitting these I noticed that the can of C1110 seems to be a bit discoloured. I should probably replace that one as well but don't currently have a part.


I ran thru' the voltage tests on pg 122 of the service manual. Both before and after all of the DC measurements were in spec for all of the lines. The AC measurements were quite a bit out and there was some rather large noise at 25Hz as well. Over the last couple of years I've occasionally had a bit of interference on some waveforms. I've not been sure if this has been injected by the USB->UART dongle that I use or whether it comes from the 'scope but I'll monitor the situation now and see if things are any different.

I guess I'll have to refurbish more of the low voltage / post regulator side of the power supply to get those AC parameters in spec tho'.


I did do one thing wrong. When I reassembled the unit I noticed that the fan was a little louder than before. So I disassembled it again and gave it a clean with a duster. It's now even louder so I guess I need to spec out a new fan as well!



Anyway, thanks to everyone who gave advice in the original thread. It was really helpful. Even if it took me a little while to have the confidence to do the fix all the answers pointed me in good directions and helped me out.

Last edited by Station X; 22nd Nov 2020 at 9:56 am. Reason: Threads merged
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Old 22nd Nov 2020, 12:09 pm   #15
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Default Re: Tektronix 2465 smoke

It is recommended to replace all the electrolytics on the power supply boards in the Tek 244x & 246x scopes (they all use the same PSU). The radial mounted Sprague caps with the red colour sealing material are the worst for cracking & leaking corrosive electrolyte under the caps.
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It's also recommended to change the caps one at a time, as one service manual has a mistake that leads to a higher & low voltage cap getting swapped, with resulting smoke on power up. Note there are two different variants of the PSU boards depending on the age on the scope, the component layout and number of non-polar caps used varies as a result.

There is a parts list & repair guide in the links from this post;
https://www.vintage-radio.net/forum/...2&postcount=14

It's worth checking the resistors in series with the two largest RIFA caps are intact, these sacrifice themselves to prevent further damage to the board.
If you have a Schaffner IEC line filter fitted then they have paper caps in them too, the one I did an autopsy on had two WIMA MP3 and an unmarked white cap.
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Which type of fan is fitted? the one with a cylindrical type motor made by Siemens or the later plastic computer type fan. The bad news is the Siemens motor is obsolete, it can be carefully taken apart & lubricated if excessively noisy, I think someone posted a guide for that too. The design of the rear cover prevents changing the type without severe modification.

David
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Old 23rd Nov 2020, 12:18 pm   #16
andyjpb
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Default Re: Tektronix 2465 smoke

Hi,

Thanks for that!

I wish that photo series has been around back in 2017 when I was first investigating. Perhaps there was another one but I never found it!

Luckily I have the plastic PC-style fan. After posting yesterday I took it back out and wiggled things around again. It's now a little quieter but I'm not sure if it's quite back to the level it was at.

I was surprised to find that my resistors seemed to be OK.

Thanks again for all the tips!

I'll use the 'scope a little to baseline any changes, especially with respect to that noise I was seeing, and then consider doing the rest of the low(er)-voltage section.
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Old 23rd Nov 2020, 3:14 pm   #17
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Default Re: Tektronix 2465 smoke

If the RIFA's filter caps don't blow themselves open circuit quick enough (when they short) the resistors will act as a fuse instead.

You are lucky with the fan type, shouldn't be too hard to replace if needed.

The other common issue with some of the scopes is the battery or Dallas RAM module (with internal battery) on the A5 boards for the calibration data (depending on the age of the scope), the early ones don't use either of these.

David
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Old 23rd Nov 2020, 3:26 pm   #18
andyjpb
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Default Re: Tektronix 2465 smoke

Hi,

I have the plain 2465 (no A or B) so I don't think I have the Dallas RAM module? Would that be right?

...so I am surprised to have the plastic fan. The ROMs on the A5 are marked 1995 on their sticker. I don't know if that's a date but, if so, I guess I have a rather late 2465?
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Old 23rd Nov 2020, 4:43 pm   #19
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Default Re: Tektronix 2465 smoke

I've not come across the Dallas RAM module in the couple I have, several have the separate battery as circled in the picture.
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And the other is an early one (no battery used) can't remember the name of the type of memory used on that one.
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I don't think there is an easy way of checking which is fitted without taking it apart, especially with the all the design changes, maybe someone else knows.

David
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Old 23rd Nov 2020, 5:06 pm   #20
andyjpb
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Default Re: Tektronix 2465 smoke

Hi,

From memory (I only had it apart two days ago!) mine looks more like the 2nd picture, including the "1995" on the white sticker. Is that a date or just looks like a date? Do you know when that one was manufactured?
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