EEVblog #695 - Mailbag Tektronix 2465 Analog Oscilloscope

[EEVblog]

Sagan & Dave take a look at a couple of Tektronix 2465 analog oscilloscopes, and compare the march of technology.
Thanks to Eric Wasatonic:
https://www.youtube.com/user/ElectronicTonic156

[con-f-use]

I swear to god Sagan looks exactly like me, when I was his age. A bit scary, actually but he's going to grow up to be a handsome lad ^^

At min 14:49 one of the diodes seems to lack a bit of solder on one leg.

[(In)Sanity]

I've got a mint condition fully functional and calibrated 2465BDM that I just love.  I still use my DS2000A series more often,  but that's just because I don't want to age the jewel of a Tek.   The ASIC's overheat without the case and the proper air flow.  Even when servicing you should have air moving over them.   I've added the heat sink to the U808 or something like that chip on the one I've got.   Great scopes.

Jeff

[(In)Sanity]

Ohh,  forgot to mention.   If that Dallas NVRAM goes..you loose ALL of your calibration.   The scope will become useless.   I've already replaced the one on mine with a brand new model,  yes they still make them.    I'm pretty good at calibrating them now,  I've done it a few times to get it perfect.   The DMM on mine was the biggest pain.   The 3457A I have was good enough for a transfer standard.

Jeff

[Gibol]

Some troubleshooting video of the newer model would be nice! I hope that you can repair one of them. They look like a decent scopes

[c4757p]

Oh boy - power's on but the fan's not. Hopefully nothing overheated.

[Howardlong]

Great scopes. I have the 2467B, same as a 2465B but with the MCP CRT for enhancing fast, low repetition sweeps. I had a 2465B for some years, and regretted selling it five years ago, so I recently bought the 2467B, when it arrived it was like being meeting a long lost twin.

I repair video would be awesome!

[guido]

You will have fun with the repairs and calibration. There is a huge thread on the forum on these scopes. Including putting a heatsink on U800. Indeed you need airflow without a case! But i've also been told that the failing of U800 has to do with the manufacturing. The older ones are made by Tek and don't fail (that much).

The 2465 is indeed missing the shielding of the PS. There is no Dallas chip, but instead there is a very early EEPROM, called EAROM. As for serial numbers, Bxxxxxx is only Beaverton. They were made in other places; the 2465 in five according to the service manual (US, Guernsey, London, Sony/Tek Japan and Heerenveen in the Netherlands). My 2465 is from Guernsey. Every location has their own serial number counting i think.

I'm not so sure i would prefer the B model.... Dallas chips that go bad (but an easy fix), leaky SMD caps destroying the pcb's, PLS logic that can loose it's content (seen it in a 2710 SA, noticed at least one of those in the video) and failing U800 chips.


 

[Fsck]

didn't someone do an MRAM or other non-battery backed ram replacement for the dallas (calling it nvram is such a lie!)?

[warp_foo]

Is it just me, or does the component at 11 o'clock to U485 @ 16:02 have an un-soldered lead?

[EEVblog]

Ohh,  forgot to mention.   If that Dallas NVRAM goes..you loose ALL of your calibration.

Not for the analog scope part though of course, that should work just fine.

[c4757p]

Ohh,  forgot to mention.   If that Dallas NVRAM goes..you loose ALL of your calibration.

Not for the analog scope part though of course, that should work just fine.

Many bits in the analog section are set by DAC, which is calibrated in software. It's only got a few pots, most of which are for nonessential things.

[guido]

Including the analog stuff. It's all calibrated in software. Even the 2465 stores calibration constants and front panel settings in the EAROM.

I have a pdf from someone on the 2465B with some common fixes. Sent me a pm if you want it. Answer will be tomorrow, it's quite late over here...

[Phaedrus]

Just a heads up, my 2465a has the same or a very similar processing board to the 2465b you looked at. And mine has main ASIC date codes of late 1986, for a model that went on sale in 1987. So it didn't take them a very long time at all to transition to the more advanced processing with SMT package chips.

[EEVblog]

Many bits in the analog section are set by DAC, which is calibrated in software.

Really?
The gain of the vertical attenuators is set by a DAC?

[(In)Sanity]

Ohh,  forgot to mention.   If that Dallas NVRAM goes..you loose ALL of your calibration.

Not for the analog scope part though of course, that should work just fine.

The analog parts are all controlled by a 12 bit DAC with a bunch of sample and hold amps.   Yes the entire scope will become useless until you re-cal it.  Well...perhaps not useless..but really messed up.

Jeff

[c4757p]

Many bits in the analog section are set by DAC, which is calibrated in software.

Really?
The gain of the vertical attenuators is set by a DAC?

No, but the gain of the preamp is. Consider - the entire front panel is scanned by an ADC - how else would the vertical VAR control work?

[(In)Sanity]

Many bits in the analog section are set by DAC, which is calibrated in software.

Really?
The gain of the vertical attenuators is set by a DAC?

No, but the gain of the preamp is. Consider - the entire front panel is scanned by an ADC - how else would the vertical VAR control work?

Actually scanned by the same 12 bit DAC acting like an ADC.   Same with the auto trigger set.   I think they used that thing in more ways that I can count.   The caps around that DAC and divider resistors are famous for leaking and throwing the reference all over the place.

[c4757p]

Yup. They definitely got their money's worth out of that DAC.

Have a look at the schematics for the input section. This isn't your standard "pile of pots" analog scope frontend.

(2445A/2455A attached as it's the only one I've got handy in PDF. 2465's similar.)

Related note: when I say entire front panel, I mean it! Those aren't encoders, those are continuous-rotation pots!

[Orpheus]

Posting to subscribe to this thread because I restored a scope of this series for my local hackerspace, but never finished calibrating it. (Some members have been using it anyway, with good results)

Anyone have a good DIY PG506-equivalent squarewave circuit? (IIRC, it calls for a 1v square wave with <1ns risetime and <5% overshoot. I'd have to look up the exact specs)

[rf-loop]

Many bits in the analog section are set by DAC, which is calibrated in software.

Really?
The gain of the vertical attenuators is set by a DAC?

There is lot of digital controls in this scope (all 2400 series analog scopes)

There is available service manual.  One version is here. If this version do not pass for version there is available very good manuals from Qservice. http://168.144.151.127/manuals/91.158.77.183/Tek_2465_Service_and_Instruction_Manual_Oct84.pdf
Chapter 5 then you know.
Also in service manual quite deeply explained how it works. (Theory of operattion, Chapter 3)

It is easy calibration using oscilloscope calibration menu and if have all needed equipments. (service mode need enable moving jumper on the A5 board)
It is real pain to calibrate if do not have suitable equipments.


Also it need note that therer is important information what also need know. So do not just open case and  jump to chapter 5 and start  cal. There is enough amount of these scopes around in markets what have burned hybrids, just because all kind of noobs think they know all how to do and manual is many times  last thing what to read - after all is loosed.

When I have calibrated these models I have used  Tek CG5011 or CG5010 etc and  external oscilloscope (yes it need also) etc it is quite easy if follow service manual  exactly including which order things need do.

[(In)Sanity]

U800 was the chip I ended up attaching a decent heat sink to.   They are a common failure point.   It's already been pointed out in this post.

https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg70295/#msg70295

Jeff

[gnif]

My first scope was a 2645A that I picked up from eBay for $300 due to displaying a fault code, so I dug out the service manual and found that the code was that the Dallas NVRam battery was low... when it arrived there was no fault, and it powered up fine, it has never missed a beat! 

[coppice]

Its hard to know what to read into instrument serial numbers, as many people start counting from some kind of random number. However, many popular high end instruments, which where made for a number of years, only reached a serial number of a few 10's of thousands. The HP history site says they only made 40k of the 1740, which was made for several years and was a popular choice for those with the budget. That makes me think the 1741 (basically a 1740 with storage tube) could only have been made in the hundreds per annum. They really made some of the exotic components for these things in amazingly small numbers.

[edavid]

I've got a mint condition fully functional and calibrated 2465BDM that I just love.  I still use my DS2000A series more often,  but that's just because I don't want to age the jewel of a Tek.   The ASIC's overheat without the case and the proper air flow.  Even when servicing you should have air moving over them.   I've added the heat sink to the U808 or something like that chip on the one I've got.   Great scopes.

This is misinformation:

1. The 2465 series scopes will run fine without the case, with no overheating issue.  You are confusing them with the 2430/2440 DSOs.

2. There is no evidence that adding a heatsink to U800 reduces the failure rate (which is not that high any more, seems like most of the bad U800s have already failed).