Tektronix TDS 684B,  Your experineces with this model? - Page 1
Forum section: electronics / testgear

author: StrayElectrons
author_rank: Contributor
timestamp: January 25, 2025, 12:10:28 am
content: I'm seeing so many 684B's on the ebay, many sellers does not clarify why it is not working or not turning on.I tried to search for some thing about this model, Tektronix TDS 684B, but not much detail about how to deal with these issues.Also what about reliability?I already have tried to search on this board too, not much.Thanks and cheers,

author: srb1954
author_rank: Super Contributor
timestamp: January 25, 2025, 07:34:02 am
content: These models store the firmware in Dallas battery backed memory, which will likely require replacement if the Dallas chip is more than 10 years old. The original Dallas chips are now unobtanium but there is a seller on eBay that makes functionally equivalent replacement modules.The electrolytic caps in the PSU should be checked and recapped if necessary before powering on. On some versions of the PSU a faulty electrolytic can cause a chain of failures of components in the PSU. Some models have RIFA caps in the PSU and these should be replaced on sight.The CRT displays in older models may be a bit tired and have a dim display or burn marks on the CRT. Chances of getting a new replacement CRT are slim but there are available LCD modules that replace the entire CRT subsystem.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 25, 2025, 11:15:37 am
content: I agree with all srb1954 said. These TDS 500/600/700 series scopes are good machines, if a bit large, once a little maintenance is done.kellyjo_13 is the seller on ebay with the replacement NVRAM chips. I can vouch for the quality, I have them in my TDS784D and TDS794D and they work great.https://www.ebay.com/sch/i.html?_nkw=Tektronix+TDS784D+700x+600x+DS1486+and+DS1250YI am currently designing my own versions of both chips, the designs of which I'll release on these forums once they are working.Check your power supply for Rifa caps (there will be 4) and replace C17, if present (Usually on the older revision PSU's used in earlier scopes like the A and B series), see the image below for details.Also, the A and B series scopes usually need all new SMD capacitors on the top Processor board, and the bottom Acquisition board, so be prepared for that too.The capacitors are practically guaranteed to leak sooner or later, so it is a definite requirement to be done.

author: Curve514
author_rank: Newbie
timestamp: February 11, 2025, 01:42:04 pm
content: I was just starting to think the same thing... It seems no one has released schematics yet.I could see a solution using 2 stacked PCBs to avoid having the DIP pins protruding the surface one. That would leave room for two cr2032 smt holders and the (normal) batteries directly in contact with the top PCB. Both PCBs could be soldered together with castellated solder points (only B+ and B-).Quote from: TERRA Operative on January 25, 2025, 11:15:37 am

author: nctnico
author_rank: Super Contributor
timestamp: February 11, 2025, 08:19:24 pm
content: Quote from: StrayElectrons on January 25, 2025, 12:10:28 amI'd stay clear from these. As these series have no peak-detect mode, they are of little use as a general purpose DSO as aliasing issues will bite you sooner or later. The color display may not be for everyone, I get an instant headache from the 'nucolor' display system. And the displays are prone to failures so replacement parts are hard to get. Another problem is that these scopes can't self calibrate.All in all, if you want 1GHz bandwidth, look for an older Lecroy or Agilent model. Preferably one with an LCD screen.