Tektronix 2212 anode lead - Page 1
Forum section: electronics / repair

author: niino
author_rank: Contributor
timestamp: February 06, 2022, 09:18:29 am
content: Hi,I just scored a Tektronix 2212, my very first own scope. It is in dire need of a PSU recap. However, I just don't manage to remove the PSU.The service manual states that the high voltage anode lead has to be pulled out of the voltage multiplier. But... this thing sits in there so tight and firm that I didn't manage to get it out there with every last bit of force I have in my muscles. Also, I am scared of breaking this thing.Removing the anode cap from the tube itself is impossible, since it is sealed and glued to the tube, unlike the anode caps I know from TVs.Any suggestions on how to do this properly? I couldn't find any kind of locking mechanism, and the service manual just tells to remove the lead with no further information given on how to do this.

author: Per Hansson
author_rank: Unknown
timestamp: February 06, 2022, 10:33:22 am
content: What about leaving the cable in place and working on the board with the flex the cable gives you?I agree that removing such cables from 40 year old equipment is not always something that ends well...Here is another thread of a 2212, seems a quite rare unit:https://www.eevblog.com/forum/repair/tek-2212-blur-jitter/

author: niino
author_rank: Contributor
timestamp: February 06, 2022, 10:38:17 am
content: I'm worried about leaving the tube charged, as I don't know whether there is a bleeder resistor. Also the cable gives far less flex than the pictures in the other thread make it seem.

author: m k
author_rank: Super Contributor
timestamp: February 06, 2022, 02:10:26 pm
content: Other thread has the lead placed pretty tightly.You can discharge the tube with a screwdriver and some wire.Just push the rod under the suction cup and ground it.The connector is usually two hooks pointing out and forced there, sometimes quite well.

author: niino
author_rank: Contributor
timestamp: February 06, 2022, 02:22:59 pm
content: There is no suction cap (as there would be e.g. on a CRT TV); the wire is actually sealed to the tube and the only way to disconnect it is by pulling it out of the voltage multiplier, sadly...

author: niino
author_rank: Contributor
timestamp: February 07, 2022, 09:53:40 am
content: Managed to get it out, but it really required a lot of force. Using a similar idea as in the first reply in this thread from Per Hansson, I disconnected everything else from the board, loosened the screws and took the board out (this was an adventure in itself because of the long power switch rod), so I could pull only at the plug on one side and directly on the voltage multiplier on the other side without the risk of breaking the multiplier or it's solder connections from the board.I have disconnected anode leads from line output transformers in TVs before (as some replacement transformers come without the lead), but none of them gave me as much headache as this one.

author: m k
author_rank: Super Contributor
timestamp: February 07, 2022, 10:00:33 am
content: Dang.My 2215A has a connector there so wrong assumption.Maybe you can add that connector.Though cutting that wire is not very tempting and it's already off.I guess you are not going to do it very regularly either.

author: David Hess
author_rank: Super Contributor
timestamp: February 08, 2022, 02:16:48 am
content: Quote from: niino on February 06, 2022, 10:38:17 amThe CRT has a resistive element between the anode and ground along the inside surface to produce the correct gradient of electrostatic field for the post deflection acceleration. It discharges the anode voltage pretty quickly.

author: niino
author_rank: Contributor
timestamp: February 12, 2022, 09:10:40 am
content: Recapped the power supply. Of all the old caps, only the axial ones were out of spec (at around half the rated capacity), and one of the output caps was very slightly out of spec (just a little more than 20% if I recall correctly). Didn't measure ESR though as I don't have an ESR meter. This however still didn't fix the issues I have (which are identical to those in the other 2212 threadhttps://www.eevblog.com/forum/repair/tek-2212-blur-jitter/). Also, it's badly out of calibration (at least my PSU recap didn't make anything worse in that aspect) so I'm starting to wonder if this scope was actually such a good purchase.Since it needs calibration anyways, I might as well try recapping the storage/CPU and the main board hoping it's just caps and nothing else. As the axial caps on the PSU were bad, there actually is probably a chance of more caps being bad.