Tektronix 2213 tart-up

[lasseo]

I had one of these handed down to me twenty years ago. I decided I should try and get it working properly, and learn to use it.



It came to me from a lab at a university, and except for needing a good clean, it looks like it has led a good life. It's been sitting on the shelf collecting dust since I got it, save for the few times I've plugged it in to check that it "works", as in, produces a trace. It does, but it is quite faint, so I've mostly left it alone.

I've been able to obtain two versions of service manuals, one through Artek Media, another done by Zenith. One of these looks like the original from when the scope was first released. The other dates a little later, October 1982, and has some revisions included. Unfortunately, while close, neither of them seem to quite match the board in mine. I suppose revisions and variations happen when a product is made in multiple locations over extended period of time.

Things that I have been able to establish:

- based on the serial number this unit is British made (no letter B at the beginning of the s/n)
- serial number falls in the range for CRT grid bias voltage modification, but it hasn't been done
- it is equipped with a preregulator board rather than current limiting board type power supply
- there are no signs of any capacitor leakage or burnt components. Insides look quite nice, with some light dust collected in the 40 years
- it doesn't make any strange noises, nor does it run overly hot
- no magic smoke released

So nothing obviously broken. I get a relatively bright trace with beam find, and that makes me think there is life left in the CRT despite not receiving the grid bias modification to reduce voltage. I suspect some or all electrolytic capacitors are going low capacitance, or high ESR, probably both.

Investigation continues.

[George Edmonds]

Hi

Go to W140.com the TekWiki site for the correct manual

G Edmonds

[lasseo]

Thank you G Edmonds.  I have checked the resource you linked, and they are a much better copy of the same two service manuals I have on hand.

[lasseo]

I found a thread here discussing low intensity, suggesting power supply issues may be the culprit:

https://www.eevblog.com/forum/repair/tektronix-2213-low-intensity

So I set about to measure the supply rails - popped off the cover, removed high voltage shield under the main board, left it on for 20 minutes to stabilise and then checked the voltages. DC readings look good, ripple not so much, assuming I have my math straight. My Agilent 1252B DMM displays RMS values, so I multiplied the displayed values by 2√2 to arrive at p-to-p values. If that's bulldust, someone set me straight now please!

Here are measured supply rail voltages vs specification:

DC Supply Rail Voltages

Test Point		High		Low		Spec		Test		OK
TP500		-8.64		-8.56		-8.60		-8.64		Yes
W985		-5.25		-4.75		-5.00		-5.09		Yes
W975		8.34		8.86		8.60		8.64		Yes
W965		-28.5		-31.5		-30.0		-30.1		Yes
W966		-95.0		-105.0		-100.0		-101.6		Yes
Headroom
TP940		-41.0		-44.0		-43.0		-		Unknown

Supply Ripple, millivolts

Test Point		Spec		Test p-p		Test RMS		OK
TP500		10		76		27		No
W985		10		8		3		Yes
W975		10		76		27		No
W965		50		79		28		No
W966		200		849		300		No

So power supply ripple exceeds the limit on all rails except one. I haven't been able to measure the headroom voltage. According to service manual, it should read around 43 V, but I don't seem to have the test points (TP940) on the main board to check it. Maybe I'm doing it wrong, not squinting hard enough? There is no potentiometer R952 to adjust it either, just a wire link across all three connectors where a potentiometer is shown on the schematic. Parts list suggests the pot was retired at some stage.

Leaky or not, I think I'd better order some capacitors then. Replace all electrolytics in power supply and on preregulator board and try again.

[lasseo]

Most of the capacitors in power supply seem to have an asymmetric tolerance specification to them, say -10%...+50%. What's with that, a nod to the manufacturing capability at the time? The oddest one are the five Mallory capacitors that are 840 uF nominal, but the tolerance is given as +10%...+100%, which suggests 924 uF to 1680 uF as the acceptable range. To replace that with a modern +/- 20% cap, I could presumably go with a 1680 / 1.2 = 1302 uF nominal capacitance. Panasonic offers 1300 uF capacitors in their range, there may be others.



I figured I would try and get replacements at the upper end of the acceptable range. I have two reasons for this. First, when capacitors age they quite universally drop in capacitance. Second, all else being equal, higher capacitance means lower ESR, which should be desirable in a switch mode power supply.

[lasseo]

I found some RIFA metallised paper caps in the power supply. I read here somewhere that they are a fire hazard, and may fail rather spectacularly when they do. In hindsight, plugging in and looking at 'er go every couple of years probably wasn't a such a brilliant idea. As you can see, cracks have started to appear on all four of these, and there's yet another one that isn't looking much better. I got lucky, this time.

[BlownUpCapacitor]

You can still get the exact same capacitor https://www.digikey.com/en/products/detail/kemet/PME271Y422MR30/1927355

But here's a good replacement that's not RIFA https://www.digikey.com/en/products/detail/kemet/PHE850EA4220MA01R17/1927361

Lead spacing on the non-rifa is a little smaller though. The original has a 10.20 mm lead spacing, but the new, non-rifa has a 10.00mm lead spacing.

But this shouldn't cause too many problems.

[David Hess]

Leaky or not, I think I'd better order some capacitors then. Replace all electrolytics in power supply and on preregulator board and try again.

That is what I would do.  Even with minimal use and no visible leakage, the aluminum electrolytic capacitors are old enough to have dried out.

[lasseo]

That is what I would do.  Even with minimal use and no visible leakage, the aluminum electrolytic capacitors are old enough to have dried out.

Agreed. I had to add a couple of Neon lamps to the list, there's supposed to be two here on the main board where it says GRID BIAS, however, you can only see one. I must have knocked off the leg on the other while removing the high voltage cage. Butcher. 

[David Hess]

Agreed. I had to add a couple of Neon lamps to the list, there's supposed to be two here on the main board where it says GRID BIAS, however, you can only see one. I must have knocked off the leg on the other while removing the high voltage cage. Butcher. 

The neon bulbs serve to protect the grid from high voltages during startup and shutdown.  They operate as zero leakage zener diodes for surge protection.

[lasseo]

The neon bulbs serve to protect the grid from high voltages during startup and shutdown.  They operate as zero leakage zener diodes for surge protection.

If I understand this correctly, then the neon bulbs would be connected parallel to grid, and light up during transients, capping the grid voltage, but do essentially nothing during normal operation.

What's the benefit of neon bulbs over zener diodes? Response time? Better control of grid voltage thanks to zero leakage?

[David Hess]

The neon bulbs serve to protect the grid from high voltages during startup and shutdown.  They operate as zero leakage zener diodes for surge protection.

If I understand this correctly, then the neon bulbs would be connected parallel to grid, and light up during transients, capping the grid voltage, but do essentially nothing during normal operation.

That is right.

What's the benefit of neon bulbs over zener diodes? Response time? Better control of grid voltage thanks to zero leakage?

Zener diodes have essentially zero leakage and low capacitance.  The DC restorer circuit which drives the grid has a fairly high DC resistance and extra capacitance would slow the unblanking signal down.

[BlownUpCapacitor]

I forgot to mention that if you haven't already, perform the CRT filament voltage mod.

https://w140.com/tekwiki/wiki/2213/Repairs

https://w140.com/tekwiki/images/1/1d/SUP3010.pdf

W140 has also linked a video with a video guide on how to do this. https://youtu.be/nTL6x8KNkh0?si=TcwhxSOM6-0gZyVc

[shakalnokturn]

Zener diodes have essentially zero leakage and low capacitance.  The DC restorer circuit which drives the grid has a fairly high DC resistance and extra capacitance would slow the unblanking signal down.

Did you mean "Neon bulbs"?

[David Hess]

Zener diodes have essentially zero leakage and low capacitance.  The DC restorer circuit which drives the grid has a fairly high DC resistance and extra capacitance would slow the unblanking signal down.

Did you mean "Neon bulbs"?

Yea, I meant "neon bulbs used as zener diodes".

[lasseo]

Well I've replaced all the electrolytics in the power supply section and the pre-regulator board now. While at it, I decided to replace the input coupling capacitors, too. One was easy as it was readily accessible on the main board, the other a bit fiddly as it was between the front panel and the PCB attached to it, and I didn't feel like removing it for just one cap.

I replaced the neon bulbs with a pair of fresh ones. The part number / designation was identical, but for some reason the replacements are about twice the size - quite a bit fatter in diameter, would not want them any bigger to fit there side by side:



The notorious RIFA capacitors were replaced with - you guessed it - RIFA capacitors. BlownUpCapacitor suggested these that were sold under Kemet brand:

But here's a good replacement that's not RIFA https://www.digikey.com/en/products/detail/kemet/PHE850EA4220MA01R17/1927361

But this shouldn't cause too many problems.

However, they do in fact have RIFA lettering on the side. Perhaps there aren't that many Y2 capacitor manufacturers around? In any case, these look quite different from the originals, with a soft molded cap sealed with goop just like any other modern capacitor, so I should think they'll be fine.

[lasseo]

I forgot to mention that if you haven't already, perform the CRT filament voltage mod.

But of course. Here it is, complete with part number modification and the wire dressed through the transformer as instructed in the service bulletin:

[factory]

The notorious RIFA capacitors were replaced with - you guessed it - RIFA capacitors. BlownUpCapacitor suggested these that were sold under Kemet brand:

But here's a good replacement that's not RIFA https://www.digikey.com/en/products/detail/kemet/PHE850EA4220MA01R17/1927361

But this shouldn't cause too many problems.

However, they do in fact have RIFA lettering on the side. Perhaps there aren't that many Y2 capacitor manufacturers around? In any case, these look quite different from the originals, with a soft molded cap sealed with goop just like any other modern capacitor, so I should think they'll be fine.

(Attachment Link)

Kemet (now part of Yageo) took over RIFA madness, not all RIFAs are bad types, the ones to avoid start with "PM" & "PZ" which are metallized paper dielectric which crack & adsorb moisture then burn up. The sooner they get discontinued the better.

The"PH" type is a one of metallized plastic dielectrics, some of which have the same see-through epoxy as the paper based ones, these are fine, note the type before rushing out to get replacements.

David

[lasseo]

One of the capacitors on the pre-regulator board was a little out of the ordinary, and after reading about its purpose (improved suppression of AC supply transients) I resorted to stuffing the old can, on the odd chance that it makes a difference in EMI performance. There's a post about it here:

https://www.eevblog.com/forum/projects/live-voltage-on-a-capacitor-can-why/

Electrical repairs completed (at least for now), I turned my attention to the appearance. The case itself looks pretty good, no scratches or missing paint, no dings or dents, just a few scuff marks and some stains that came off with soapy water, IPA, and elbow grease.

The screen had a few faint scuff marks and a spot with cataract-esque discolouration, so I removed the bezel to have a closer look. Luckily for me, the CRT and graticule on were both flawless, save for some fine dust that were easily cleaned of with a Lens Pen. All the blemishes were on the blue filter screen that sit in front of the CRT, so I decided to give it a wash and a polish using a headlight restoration kit that I had sitting on a shelf as leftovers from a couple of years back. I ended up not using the scouring pads, just a bit of the polishing compound and a soft cloth was needed to get the filter glass (well plastic) back to looking splendid.

   

Front panel on the other hand, with all the switches and adjustments was quite filthy, as you can see in the "before" photos. It must have caught overspray of some sort at some stage; similar droplet stains were on the case. That's not blood droplets from an injury in a workshop is it...?

Before:
   

After:
 

I applied the a similar soapy water - PCB cleaner - elbow grease recipe, with similar results. I say similar, as you can see the face is clean and presentable but I have removed the time base button. That's because I added IPA here and there for stubborn stains which in hindsight I shouldn't have. As I discovered - and is apparently well known in Tek circles - IPA can easily lift off the screen printed lettering off the rotary switches, which it did on the time base button.  Presumably this happened because I left the solution brewing for too long in the small gap between the front panel and the switch. A simple google search - in advance thanks very much - would have saved some trouble here. Butcher.

[lasseo]

With mechanical clean-ups out of the way, I carefully re-assembled the scope - preregulator board back to where it belongs, re-attach its four jumper leads, re-install high-voltage cage and brace. I left the cover off but gave it another vacuum to remove any solder or other residues, another visual inspection before plugging it in and turning it on. I did so from what I considered a safe distance. I wasn't hissing at me, it didn't go flash-bang, altogether very uneventful. Great, I thought, this is exactly what we want.

Well, sort of. On closer inspection, there was nothing on the screen either - nada. I let it warm up the indicated twenty minutes and checked again. Still nothing. Beam find produced a relatively bright blob about 5 mm in diameter, but none of the other settings seem to have any effect. It didn't seem to matter whether I feed it with the internal probe adjust or an external signal from a generator. A quick check with DMM indicated they are all present and close to the values I observed before. That probably means the power supply survived my resuscitation attempt - good.

Time to take a leaf out of Edd China's book, take a break, make a brew, and have a think.

[lasseo]

Eppur si muove! We have a trace!



Having slept over it, I realised I had - of course - done more than just replacing like-for-like parts. While at it, I had completed the CRT filament voltage modification. It would likely change the display brightness. Further, the Service Manual clearly states  that every time anything is done to the power supply section the scope should be re-calibrated. One of the first steps in the calibration is - you guessed it - setting up proper limits for the trace brightness adjustments. About a sixth of a turn on Grid Bias potentiometer brought the display back to life. Feeding with the internal 1 kHz probe adjust I now have a nice steady trace of constant brightness for everything except for the slowest time setting, so the sweep time compensation seems to be working too - excellent!

[BlownUpCapacitor]

When I performed the CRT filament mod, I didn't notice any change in the CRT performance. Originally, the filament was being over driven, and could easily burn out.