Fix an old Tek 475, or buy a 2246A/2247A ? - Page 1
Forum section: electronics / testgear

author: techydude
author_rank: Unknown
timestamp: September 25, 2013, 01:32:52 pm
content: Hi guys,I have an old Tek 475 scope (2ch, 200MHz ?, probably early-80s birthdate) gifted to me 10+ years ago, & sitting disused ever since, and was probably unused for most of the decade before that by its original owner (ie. no TLC / repairs / calibration) in 20+ years. I've tried using it a couple of times recently, but it's pretty crappy (not the 'scope, just its current performance!) - most of the switches & dials are very noisy, and just tonight it looks like the horizontal sweep appears to have stopped workingNow I'm reigniting my old career in electronics, I have a need for a scope. Back in the day I had a 2246 (or 2246A) where I worked, which was just lovely. I don't have the $ ready for the $1-2k for a Rigol 2xxx DSO yet, but I'm also in the same camp as Dave in thinking it's a good idea to have a decent analogue scope on the bench alongside a DSO anyway. My interests span not just microcontrollers & basic digital, but "analogue" (nothing terribly exotic) & power electronics (switch-mode PSUs & motor drives etc), & looking to poke around in decent speed FPGAs too. Not really into radio/video.So I'm wondering, should I:(a) get this 475 fixed / cleaned / calibrated, and if so, what's that likely to cost? how much can I do myself? etc (remembering, I don't have any other scope to use to fix it)or(b) spend $300-500 on a 'known good' 2246A/2247A on eBay (closer to $400-500 for the 2247A, &/or if shipped from US), & put the 475 on the back-burner as 'something to play with' at my leisure to get it back to health?or...?Appreciate your thoughts.Anthony.

author: VA3SU
author_rank: Newbie
timestamp: September 25, 2013, 06:09:28 pm
content: A scope on ebay that is "known good" is a crap shoot if you ask me. Lots of good scopes on there but you get what you get. I worked for 30 years with many of the best scopes money can buy ( at Raytheon) and I could not be happier with my rigol DS2072 for what I need a scope for here at home.Save your money and get a DS2072 or one of the other faster scopes in their lineup if you need the speed, more than one way to do that also...Then fix the 475 and sell it on ebay as know good.Regards,Kevin

author: JonnyBoats
author_rank: Regular Contributor
timestamp: September 25, 2013, 07:41:08 pm
content: If it were me I would at least open the scope up and clean it. Spraying contact cleaner into the switches may help alot.If that doesn't work you wouldn't be out much money

author: Marc M.
author_rank: Regular Contributor
timestamp: September 26, 2013, 03:14:11 am
content: Quote from: JonnyBoats on September 25, 2013, 07:41:08 pmDo not use contact cleaneron these scopes! It will damage the PC Boards. You can use it on the switches that are not mounted on the boards. The vertical amplitude and horizontal time base switches are cam switches which depress very fragile gold contacts mounted directly on the board. Tek recommends using isopropyl alcohol as a cleaning agent. It is time consuming and delicate work requiring disassembly/removal of the entire front panel. Once apart, I slid strips of copier paper dampened with alcohol between the contacts while gently depressing the upper contact to clean them. I repeated the process until the paper came out clean. The contacts are very fragile and easily bent/distorted so great care must be exercised during the process. The other common issue with the Tek 4x5 series is caps failing. Many owners replace the filter caps right off the bat. The several I worked on didn't show abnormal ripple in the supplies so I didn't replace those. The units I worked on all had a number of failed tantalum caps. These things are filled with them! Fortunately, the power supplies are very well protected preventing any failed caps from Chernobyling and damaging the board and/or associated components. Once they have been repaired, they are some of the best portable analog scopes ever produced and in my opinion, well worth the effort to repair.

author: PaulAm
author_rank: Frequent Contributor
timestamp: September 26, 2013, 01:06:58 pm
content: Most of the noise in the pots can be handled by rotating them through their range a hundred or so times.The attenuator and timebase contacts are as Marc said. They should be cleaned only with isopropyl alcohol and a tiny piece of copier paper. You can get to the attenuators without taking too much apart.The filter caps are a widely known problem. Not really a surprise I suppose, the scopes are 30 years old. Probably a moderate level repair, but not really too bad. Lots of writeup available if you want to see what's involved.

author: mazurov
author_rank: Frequent Contributor
timestamp: September 26, 2013, 04:04:27 pm
content: This is how I clean contacts in my 475A( see attached picture ). I first raise the contact using the corresponding control, place a piece of paper underneath then lower the contact and pull the paper out. I use Caig DeOxit, doesn't seem to make any damage, for 5+ years now.If you're doing any line-powered circuits I suggest keeping this scope - no modern instrument will give you the input range of 50mv - 100V per division (with 10x probe).

author: mzacharias
author_rank: Frequent Contributor
timestamp: September 27, 2013, 10:54:51 am
content: Quote from: mazurov on September 26, 2013, 04:04:27 pmI would love to see more pictures detailing the procedure for dis-assembly and for cleaning these switches. My 465 is good, but I would love to learn some of the old Tek tricks.

author: techydude
author_rank: Unknown
timestamp: October 03, 2013, 06:59:37 am
content: Thanks for all the feedback guys, most appreciated.OK, I'll keep the 475 for a fixeruperer project, I should have a bit of time before the year is out to do that.For complicated financial reasons, springing for a Rigol DS2xxx isn't a near-term option, so I'll probably do the crap-shoot thing on a 2246A... wish me luck! lolAnthony.

author: techydude
author_rank: Unknown
timestamp: October 10, 2013, 12:50:15 am
content: P.S. the DS1000Z range just came onto my radar in the last several days, and the Money Fairy paid me an unexpected visit, so I'll hopefully have a DS1074Z in my hands by the end of next week! It is with both trepidation & The Warm-Fuzzys that I look forward to bringing the 475 back to scratch now

author: madshaman
author_rank: Frequent Contributor
timestamp: October 10, 2013, 01:00:21 am
content: 475 is a really nice scope :-)