TEK T935A Seized Time Base Position Control - Page 1
Forum section: electronics / testgear

author: Cliff Matthews
author_rank: Unknown
timestamp: June 05, 2019, 12:35:59 am
content: The <---> control turns and works, but requires8x more forcethan the other pots to turn. I took off the left side panel and the control seems to be un-accessible under several PCB's.. It seems there's very little structural frame work, such that it requires the right panel to even stay together (and this thing is in great condition).1) When I decide to carefully pull out the rest, will De-oxit be the best spray to use?It has no 50 ohm termination switch on either channel..2) Will 2x 100 ohm SMT resistors soldered inside the barrel of an old Arc-Net "T" cause signal reflection below 20Mhz?

author: tautech
author_rank: Super Contributor
timestamp: June 05, 2019, 02:07:02 am
content: Try only removing the knob and floating some low viscosity lubricant along the shaft. Deoxit might be fine and plain ol' WD40 would be too.Not too much as you just want to add a little lube in case the shaft has 'picked up' in the pot.Gently gently work it back and forth and you might be able to coax it free again.Good luck.

author: Cliff Matthews
author_rank: Unknown
timestamp: June 05, 2019, 02:49:41 am
content: Well, I got the shaft!It's like custom un-obtanium fiber/plastic. I got a T932 PDF so I'll have to read and disassemble.

author: tautech
author_rank: Super Contributor
timestamp: June 05, 2019, 03:25:23 am
content: Quote from: Cliff Matthews on June 05, 2019, 02:49:41 amAh OK, the pot is near the rear .....still a trouble to get at ?

author: Cliff Matthews
author_rank: Unknown
timestamp: June 05, 2019, 11:39:52 am
content: I'm on course today, so later I'll do some reading and maybe this evening I'll figure-out how to separate-off the right panel. That seems to be key in what holds all the entrañas (guts) together. Worse come to worse, I'll have to buy one of your 1104x's to cure my sadness for having destroyed it..

author: tautech
author_rank: Super Contributor
timestamp: June 05, 2019, 11:45:42 am
content: Quote from: Cliff Matthews on June 05, 2019, 11:39:52 amNow don't go doing anything too radical !I'm only here to help bounce things around as discussion can help to see the light.Truth be known I've got a soft spot for Tek stuff, well some Tek stuff and that includes the busted TDS2012B I have that was my first DSO.Anyways, the day is nearly done for me so we'll see how you're progressed in the (my) morning.

author: Cliff Matthews
author_rank: Unknown
timestamp: June 06, 2019, 02:46:58 am
content: Thanks, you were right, a little oil unseized it after a few turns.

author: Cliff Matthews
author_rank: Unknown
timestamp: June 06, 2019, 02:49:18 am
content: 2 more beauty pics.

author: Cliff Matthews
author_rank: Unknown
timestamp: June 06, 2019, 02:55:14 am
content: 2 more just for a complete set. I have someMG Chemicals 409B Electrosolvearriving tomorrow, so I'll leave the panel's off in case anyone wants a close-up.

author: Rollin Hand
author_rank: Regular Contributor
timestamp: June 12, 2019, 02:04:04 pm
content: On my t935 the rubber foam arround the crt deteriorates ,making it loose.I put a cuple of turns of doble sided tape.Did you check yours for this issue?

author: Cliff Matthews
author_rank: Unknown
timestamp: June 12, 2019, 08:57:37 pm
content: Mine has no foam.. it's more like a flexible plastic shroud. It has 2 Tek service tags from 1990 (so maybe they upgraded?)Right now, I'm wondering how to fix a broken nylon flex link connecting two metal collars (for red channel 1 vertical fine pot) and super-glue doesn't work..

author: tautech
author_rank: Super Contributor
timestamp: June 12, 2019, 09:09:55 pm
content: Quote from: Cliff Matthews on June 12, 2019, 08:57:37 pmWhat size is the shaft ?Flexi couplers are available online.........I'll come back with a link from another thread.

author: Cliff Matthews
author_rank: Unknown
timestamp: June 12, 2019, 11:11:39 pm
content: Quote from: tautech on June 12, 2019, 09:09:55 pmBoth pot and shaft sizes are 3.12 mm (1/8") with collet OD of 10mm and both together are ~12.5mm length.Since the front shaft is plastic, I see no need for a weak insulating nylon link piece. Are spiral stepper motor couplers OK?

author: tautech
author_rank: Super Contributor
timestamp: June 12, 2019, 11:35:32 pm
content: Quote from: Cliff Matthews on June 12, 2019, 11:11:39 pmhttps://www.eevblog.com/forum/testgear/hameg-408-1a/msg1202657/#msg1202657

author: Cliff Matthews
author_rank: Unknown
timestamp: June 12, 2019, 11:45:58 pm
content: Thanks! This coupler looks about right (price too..) although OD of 19mm would bring it 4.5mm closer to the aluminum shield.https://www.amazon.ca/3x4mm-Coupler-Flexible-Coupling-19x25mm/dp/B01LXWXF6XThere's a good idea there on using heat shrink. I'll cut tin-foil to slip in behind so I don't melt any bjt's in the front-end.*Done with my last bit of heat shrink big enough, but it slid-upward too much. It'll work and I have an excuse to buy more :-)

author: tautech
author_rank: Super Contributor
timestamp: June 13, 2019, 12:16:39 am
content: Quote from: Cliff Matthews on June 12, 2019, 11:45:58 pmDoes it really need to be flexible ?Maybe something more basic and smaller diameter like this: (from the same thread)

author: Cliff Matthews
author_rank: Unknown
timestamp: June 13, 2019, 12:47:47 am
content: The length of 25mm would take it all the way from the pot to up under the shield where the 19mm OD would scrape. Also, both shafts are 3.12mm so the 2mm would need a little boring-out.Until I get a swanky SDS-1104-x, a little better job on the heat shrink works for me..