1960's Tektronix 422 Oscilloscope re-cap

[lordvader88]

Just  got it, it supposedly worked and show both traces at least, so the seller said. ATM I need to solder on a 3-pin plug, I only have modern ATX style and they don't fit.

But it will also be full of 1960s electrolytic caps (I've taken off the back cover and the big input filter elec. caps there look ordinal, metal-can, big axial type fitting perfectly in the holders.


I don't have near enough random big elec. caps of mains input levels. I have the schematic.

So far just using sandpaper to clean off the rear plug. And know what side has the fuse on it, and the fuse is fine. Haven't looked at the sch. yet tho, how are the switches connected, idk yet. The plug retapticale/pot seems to be riveted to a back plate (that I've unscrewed) so I could just solder onto the plug posts for now or cut the inside wires.........the add said it had no plug


SHould I power it up for a minute? I most confirm what the seller said of it working condition.

[lordvader88]

It looks well used, actually well abused, all scuffed up, scratched up, even FP knobs/buttons melted. I measured the 4 big caps I can see, they measure right with a DMM.

But I'll replace all them anyways, not worth the risk, they wear out

[The Guy]

It looks well used, actually well abused, all scuffed up, scratched up, even FP knobs/buttons melted. I measured the 4 big caps I can see, they measure right with a DMM.

But I'll replace all them anyways, not worth the risk, they wear out

I have one of these.... and it works just fine. No recap needed whatsoever. These are very sturdy long lasting pieces of equipment

Very beautiful little scope

[lordvader88]

It never worked. I screwed it back together with the fully chasis back together, and soldering in a 3prong plug. 115V measured across its plug, pulled a little FP switch out, that says 'power' and waited a few moments, no traces,,, the CRT gives off a tiny amount of light.... but no hint of traces



wait now I (lack of CRT light is bad) but I never tried centering anyting....still hope yet

[lordvader88]

it doesn't work. wired in 115V, and the CRT screen gets a ;little brighter, but thats it

orange pwr light comes on


I had a bit of a trace for moment after playing with some buttons.

Intensity/focus/etc seemed to do nothing

[The Guy]

Do you have the service manual? First thing to do is to measure the output power supply voltages at those line nodes.

Start by getting the service manual at http://bama.edebris.com/manuals/tek/

... I think they have it.

[lordvader88]

Yeah thanks I have it.

And just plugged it in today for 1/2 second, and heard a weird noise like scratchy rumbling....and some smoke/wax wafted out the side. The fuse never blow, but did warm up.

It begins. Hope I didn't wire mains in backwards, I put hot on the fuse side.  there'a an X cap, then a common (or diff.) choke., fuse then transformer.

The longest it was plug in and on was last night for maybe 30s-1min Today it wasn't even turned on.

Sounds like a capacitor going

[Cyberdragon]

Getting the mains backwards shouldn't cause a problem, transformers and X caps don't care. The noise was either a cap shorting out and burning up or something high-voltage arcing over and burning up (hopefully not a transformer), just look for physical damage somewhere.

[The Guy]

yea... also check for burned resistors... mine had 3 carbon comp resistors burned up in the power supply when I first got it.

[lordvader88]

Yeah and I have 2 very different schematics (at least at the PSU) for a Tek 422, both with the Tektronix name all over the pages and called 422, maybe 1 is a lab model or something, mine doesn't have an x-cap or choke, its just a fuse, and a thermal switch straight into the trans.

I have the right schematic, and the pictures match. However I'll wait till tomorrow when I get a small lightblub limiter, setup, the thing uses about 25W, and
I'll fire it up and very quickly check a few voltages off multiple secondary outputs.

[The Guy]

Before firing it up again i suggest to perform a very detailed visual inspection. I like to use an 5x optivisor, helps a lot when trying to find screwed up stuff.

Visually check every carbon comp resistor, transformers and caps from the power supply. There is a high chance of finding the source of the noise that way i think.

I´m not expert but i´ve successfully restored three scopes last month (with the invaluable help from the guys here), and currently i am restoring my fourth