Arcing? in Tek TDS684C Scope - Page 1
Forum section: electronics / repair

author: stardropqi
author_rank: Newbie
timestamp: October 15, 2023, 11:42:22 pm
content: So I have this Tektronix TDS684C scope from a relative. Its old, so I dont have any documents of it, or any knowledge of what options it has . However, when turned on, I hear what seems to be arcing and the display does not light up, the front panel buttons do glow, however. I opened it up a bit ago and there were no signs of damage in the Display Assembly. I took a photo of it, I will edit this post with the image soon.I am a bit afraid to turn it on with the CRT driver board opened up unshielded, but if need be, I can open it up. I don't have any other scopes/signal analyzer, I only have a multimeter and soldering equipment.Service Manual:https://w140.com/tekwiki/images/3/31/071-0627-02.pdf

author: stardropqi
author_rank: Newbie
timestamp: October 15, 2023, 11:47:03 pm
content: Okay, can’t figure out how to edit on mobile, but here is the one (and only) photo I have from a while ago. It takes a while to open this thing up, so I might respond slow.Actually, the transformer looks a bit damaged on the top, not sure if that is pertinent.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 17, 2023, 12:10:53 am
content: Yes that looks punctured. If you want to be sure turn it on without the cover, just don't let your fingers in the wrong place.A replacement transformer may not be that easy to find, you could try repairing by enlargening the hole to remove the charred plastic and filling with epoxy. Make sure epoxy has fully hardened before testing.I've had luck on higher voltages than this with epoxy.Of course this only works if there's no damage to components in the flyback transformer.

author: stardropqi
author_rank: Newbie
timestamp: October 17, 2023, 12:22:00 am
content: Thanks for the reply!I’m not even sure if the scope will power up the driver board without other items connected because all the main boards are stacked on top of the metal chassis that holds the display assembly. I will try that tonight, hopefully I can repair this scope.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 17, 2023, 10:53:53 am
content: PM me if ypu need a new CRT board. I have spares.

author: stardropqi
author_rank: Newbie
timestamp: October 18, 2023, 02:14:54 am
content: Thanks for the offer TERRA, may consider itSo here are some photos, but I think I have bad newsIt doesn’t look like the CRT driver can get power without the main board attached… which covers up the driverThe flyback does look pretty punctured, and the red anode lead looks blackened, what could have caused that?

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 18, 2023, 05:27:50 am
content: The CRT board runs off power supplied through the grey ribbon cable from the main board.It is possible to remove the CRT board and sit it on top of the main board with a piece of plastic or cardboard etc between for insulation and run it like that.Or you can make extension cables for the ribbon and coax to give more flexibility for bench testing.I know the black and white scopes of this type had a known problem where the flyback transformer would fail, but the colour ones were usually pretty reliable.I guess you just got one of the unlucky ones...The darker colour on the red HV lead is just dust. It's common on these cables and can be cleaned off easily if it bothers you.You'll need to source a new flyback transformer at the least.Whether CRT damage is to blame is yet to be seen once you power it up with replacement parts.

author: stardropqi
author_rank: Newbie
timestamp: October 18, 2023, 05:38:57 am
content: I think I have another color TDS6XX sitting around somewhere with some processor fault… Maybe I can source a flyback from somewhere else thoughIn other words, I have disconnected the CRT board to verify the scope actually works, and with an external VGA display it seems to be good!Thanks for the responses!

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 18, 2023, 09:12:49 am
content: Yeah, if you can swap parts from another scope, that is the easiest way to see what's up.My offer still stands, for the cost of shipping (from Japan, but it's not toooo expensive for the slow option) plus a bit extra for some beers and the CRT board is yours.