Tek 2212 blur / jitter

[kevbry]

Hello,

I was just given a well used Tektronix 2212 digital/analog scope. The trace itself is nice and sharp, and aside from a loud fan and the timebase encoder needing a cleaning, it seems to be in good mechanical shape.

However, there seems to be a "smearing" effect of the settings text displayed on screen that follows the trace as it's swept across the screen. When the trace is at the left of the screen, each digit is blurred out towards the left side of the screen. Once the trace reaches the right side, the digits look fine until the next sweep starts. The smear matches up perfectly with changes to the sec/div setting. The smear goes away when I switch to DSO mode or if I switch to single shot. Video is down below.

There's also a constant horizontal vibrating / jittering effect on the digits of the settings displayed on screen. It's more pronounced towards the bottom of the screen, and occurs in both analog and digital modes. It's a lot more noticeable in the digital mode due to the smearing effect disappearing. The jitter doesn't seem to be affected by any settings changes like the smearing effect is; it's pretty much constant.

So far I've followed the golden rule and checked power supply voltages. Nothing seems out of the ordinary, though I can only guess at a few of them, since the manual I found doesn't have any schematics. I'm going to clean out the encoders on the front panel, since all three of them seem a bit gritty and are skipping positions. I'm waiting on an ebay reprint of the full manual, but if anyone has any ideas about where to start with either of these I'd appreciate it.

Video of the blurring issue at around 0.1-0.2sec/div. So far haven't been able to get a decent video of the jittering issue.
https://youtu.be/0Bsq-lSoUPg

[tautech]

So far I've followed the golden rule and checked power supply voltages. Nothing seems out of the ordinary, though I can only guess at a few of them, since the manual I found doesn't have any schematics.

Try this one:
http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/2213.pdf
Sorry 83 Mb.

This can be useful too:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[MrSlack]

One of my Tek 465B had horizontal jitter like that until I replaced all the power supply caps. Check the power supply ripple as well as voltage. You will need another scope. Stick the other scope on the DC test points in AC coupled mode at 2v/div and reduce slowly until you see ripple. Check against acceptable limits in the service manual. If it's bad then replace all the smoothing caps on the DC end of the scope. You could probably use an ESR tester but might as well just flat out replace them all anyway. Use 105oC caps that are rated for at least 50% higher than the old ones voltage wise and at least 1.5x the value and are low ESR.

Also if it has a CRT grid bias trimmer, look in the service manual for the calibration procedure for that. A lot of ghosting and smearing is due to incorrect grid bias. It is possible that the phosphor is knackered as well - it doesn't last forever.

Cleaning is a good bet as well - IPA + printer paper works well - nothing more abrasive. Watch out for loose screws as well; they cause all sorts of odd ground loops.

Also when it's uncased and cold, expect some odd behavior. Scopes tend to be sensitive to interference and temperature, especially old ones.

[kevbry]

Thanks for the help! I have an ESR meter on the way, so I'll check all the caps I can once it gets here. Will check ripple some night this week.

I took out the front panel board, and found that the rotary encoders for vertical and horizontal divisions are all heat welded together and sealed. Not sure how I'm going to go about cleaning them without taking them apart at the moment, and they seem to be tek specific, of course. I'm reading through the mechanical restoration thread looking for ideas.

As far as manuals go, I haven't been able to find one so far where the schematic bears much resemblance to the 2212. I've checked out most of the 2200 and 2300 series manuals and haven't come across one that seems close enough to use. The 2232 seems to bear the most outward resemblance, but its internal construction is very different (attenuators on separate boards instead of everything on the main board with the 2212). I did find at least a few more test points on the main board itself, but most of the ones mentioned in the manual point to a pin of a specific IC, which I can't seem to find labeled on the board. I'll take some pictures tonight in case anyone can recognize a similar model that I might have missed.

Edit:
After a bit more searching, the 2212 appears to be very similar in construction and outward operation to the 2211. Service manual for the 2211 seems to be non-existent as well, so I'll have to wait for the 2212 manual to arrive.

[Tappy]

Regarding the 'horizontal vibrating' effect, have you tried switching off other gear that's close by (bench PSUs etc)?  It sounds like 50Hz EM field from a transformer.

[kevbry]

I actually wondered about that as well. I unplugged everything else on that circuit and even unplugged the nearby fridge, but it had no effect on the ghosting or vibration. As far as I could tell there wasn't anything else drawing power in the house at the time I was testing it out. That said, I might bring it in to work and try it out there, just to make sure.

[kevbry]

Reading through tekscopes mailing list it appears that the 2212 is fairly rare, and was designed by former Telequipment engineers in England. Mine was manufactured in Holland around 1992-1993.

Chassis without storage board or front panel:


Power supply:


Storage board, complete with the only two bodge wires in the whole unit:


Main board:


Front panel board:



Front panel switches appear to be identical to C&K RTA series. Exactly which model will be fun to find out. Probably going to desolder one and check the pinout - all three are an identical model number in the manual.
http://www.digikey.com/catalog/en/partgroup/rta-series/20376


Album: http://imgur.com/a/oMr7J/all

[tautech]

Reading through tekscopes mailing list it appears that the 2212 is fairly rare, and was designed by former Telequipment engineers in England. Mine was manufactured in Holland around 1992-1993.

If it was they certainly learnt heaps, far better than any TQ stuff I had.

PCB's look very nicely laid out and will be great for rework if needed, note the proliferance of axial MLCC caps and very few electrolytics. Not sure if I like all those round axial tantalums. 
I hope you get schematics.

BTW nice pics. 

Edit
Note the coloured transistors, this identifies the gain range they are selected from. eg. 300-400 Hfe etc.

[MrSlack]

Nice photos. My first scope was a Telequipment D83. Well I say mine, but it was my father's and I used it more than he did. Was actually rather nice compared to most of their units.

[tautech]

Nice photos. My first scope was a Telequipment D83. Well I say mine, but it was my father's and I used it more than he did. Was actually rather nice compared to most of their units.

Snap.
Mine too. 

[kevbry]

Edit
Note the coloured transistors, this identifies the gain range they are selected from. eg. 300-400 Hfe etc.

I always wondered about that... any idea if there's a legend or list of exactly what the colours map to, or is it a per-model thing?

LCR meter showed up today, other scope is ready to go to test out the voltage rails for noise. Will at least get a start on it tonight. Manual hasn't arrived yet, and I haven't been able to get the front panel encoders cleaned up so I'll just have to deal with them being jumpy for the time being.

[tautech]

Edit
Note the coloured transistors, this identifies the gain range they are selected from. eg. 300-400 Hfe etc.

I always wondered about that... any idea if there's a legend or list of exactly what the colours map to, or is it a per-model thing?

The availability of a device in a range of gains is not as common as it once was and this info is normally found in the manufacturers datasheets with sometimes only a brief mention. A suffix to the device # also is used to denote the gain range too.
Often one must substitute for replacements taking care to match all parameters as closely as possible including gain.

Of course OEM use of these types of devices (narrow range of gain) was to tighten circuit tolerances for improved stability and/or accuracy.
One still sees selected devices in analogue appliances, commonly amps.

[kevbry]

Short update. Didn't end up having enough time to reassemble, but did have enough to desolder one of the rotary switches.

Pulled out the switch, found that only 6 of the 14 pads were actually connected, and 2 of those were to each-other. Switch is 16 position, so I matched up the pin labels moulded into the bottom of the switch with the ones from the C&K RTA series datasheet; they were the only switches I could find that looked identical. Everything matched up exactly with the 16 position BCD switch model, so I thought I had a winner, but I thought I might as well test it out to be sure. Rigged up some LEDs on a breadboard, and...



Gray code... Damn! Can't seem to find a compatible footprint switch that isn't BCD, so I guess it's time to start figuring out how to clean them or fire up diptrace and make an adapter board.

[MrSlack]

Can you find a replacement encoder board at all? Qservice.tv carry stuff like that.

[kevbry]

I actually did manage to clean them in the end. I started poking around at the one I'd desoldered, and I guessed that it was only welded at the corners if it was at all - the moulding quality is very high, so they fit together almost seamlessly. I wedged a set of flush cutters in and managed to pry the top off. I immediately regretted this decision... 14 tiny wipers went flying across the desk.

I don't have any images of the inside of the switch (left the camera in high speed video mode... about 10 seconds of footage), but I found an image online.



The encoder disk was filthy. The wipers and disk are silver plated, but they had some orange/pink tarnish or deposit all over them. On the one I desoldered cleanup was rather easy with nutrol and IPA, but reassembly took over an hour due to the tiny pieces and no idea what order they were supposed to be in. Ended up sticking all the pins in a protoboard and soldering them down so I could put the disk and case back on.

For the other switches I just left them in the board, took all the panel buttons off and pried the top case and spindle out, leaving the wipers and disk attached to the board. This made cleanup a bit trickier (lots of electrosolv and IPA wetted paper) but reassembly was a snap. Put everything back in the case, and I have almost perfect horizontal and vertical control with no skips.

Tested the voltage rails with a multimeter and they're all within 0.5V of where they're supposed to be. 15v showed up to 100mv on AC, so that's where I'll start with the scope this weekend. Tried adjusting grid bias as someone had suggested before, but didn't end up having any effect on the ghosting or shudder.

[MrSlack]

Nice work. Def power supply caps if there's 100mV ripple.

[Cubik]

Hello Everyone!

I am about to repair a Tektronix 2212 that suffers of a faulty power supply.
After a visual inspection, I noticed a couple of blew-up chokes that need to be replaced. Maybe some caps as well.

My problem more on the ‘Mechanical’ side.
I need to disassemble the FOCUS knob and the POWER SWITCH from the Power Supply board without breaking them so I can remove the Power Supply board from the frame and proceed with the repair.

I am obviously missing something here and any help would be very appreciated.

Thanks! :-)

[kevbry]

You should be able to just pull both of those straight forward out of the control panel.

[Cubik]

...well, maybe for the FOCUS knob only then but I really feel it is going to break if ii do that.
There is no way you can pull straight the POWER SWITCH. it is a push button with a long bended rod attached to the actual switch on the board with a spring system...
It has to be a proper way to disassemble that...

thank you for your help anyway.. :-)

[niino]

I had the same issue on mine and found the problem working together with an actual expert. It's a trimmer capacitor in the horizontal output amp, C710, that was badly misadjusted. It's not a power supply or electrolytic capacitor issue (there were out of spec electrolytics, but replacing them didn't fix the smearing), but a calibration issue.