Advice requested for minor repairs on Tektronix 465 scope - Page 1
Forum section: electronics / repair

author: handyguy
author_rank: Newbie
timestamp: January 19, 2019, 06:03:28 pm
content: Hi all,I have some basic repairs I am considering for my newly acquired mostly functional 465, serial# >250000.1. CH2 vertical attenuator cleaning (50mv/100mv/200mv setting shows a nearly flat line until the scope is warm) - Could anything else cause the 'flat' line?2. CH1 X1 volts/div bulb replacement (assuming it’s not a transistor; the X10 bulb goes on when probe contacts are shorted)3. Most pots are sticky and make fine adjustments difficult (clean the sealed pots; suggestions are to back off the screws or drill a hole)Items 1&2 require removal of the Vertical Preamp board. A few items in the TEK service manual are of concern for my average soldering skills!• Unsoldering (a previous repairer soldered them in!) the delay line from the back of the board (is this needed? – one could possibly maneuver the board out for cleaning the attenuator and accessing the bulb fixture)• Unsoldering the coupling capacitors from the front panel BNC’s. There are some small resistors and limited access in there. This worries me the most.• There is also some bodgy wiring with red/clear tape to prevent shorts from the resistors to the attenuator covers. Is this TEK original? Can someone supply a photo of what it should look like?Thoughts?

author: rhb
author_rank: Super Contributor
timestamp: January 19, 2019, 11:04:04 pm
content: You should ask on the Tek mailing list, TekScopes on groups.io. Make sure you read the manual thoroughly *before* working on the attenuators. Do *NOT* spray them with tuner cleaner.Reed Dickinson is on the groups.io list and refurbishes Tek scopes and sells them on eBay. He can advise on retensioning and cleaning contacts. Closing the switch on a piece of bond paper and pulling it through is a safe method and 99% isopropyl a safe solvent.If the scope has been in a humid climate the transistor leads tend to corrode in the sockets. They often need to be wiggled a bit, i.e. pull almost out and push back in a couple of times.I had a delay line fault on mine. When I went to resolder a resistor it fell completely out of the board on to the bench.The retired Tek service guy I went to for advice before starting on repairs on mine clapped his hands against the opposite sides of the scope and beat on the edge of the frame with a small piece of broom handle or such to check for intermittent connections of which I had many. But it also verified that the scope was basically functional except for a dozen or so broken solder joints and other intermittent connections.You will probably find more faults when you go through the full calibration procedure. I highly recommend getting one of Leo's 40 pS pulsers from leobodnar.com. I'd offer you a Tek 106, but shipping would probably be prohibitive and it would probably need TLC. I'm in central Arkansas, USA.A cracked solder joint in the vertical amplifier signal path would make contact once it warmed up a bit. So that's a high probability explanation. Identify the signal path for CH2 and gently flex the board with a bamboo chopstick or similar while it is in the flat line state. That will verify the cracked solder joint hypothesis.

author: handyguy
author_rank: Newbie
timestamp: January 19, 2019, 11:55:47 pm
content: Thanks for your reply; I did post on groups.io, but had no response after several weeks.

author: PaulAm
author_rank: Frequent Contributor
timestamp: January 20, 2019, 01:12:52 am
content: Post again. I usually look at anything with 465 in the subject line and I don't recall seeing it go by.Cleaning the attenuator contacts is very fiddly work but can make a real difference.

author: rhb
author_rank: Super Contributor
timestamp: January 20, 2019, 01:13:57 am
content: I don't recall seeing it. Did it actually get propagated?You might have asked the question in such a fashion that no one had a clear notion of the question. 465 posts are pretty common.

author: handyguy
author_rank: Newbie
timestamp: March 06, 2019, 06:33:50 am
content: Thanks, i have re-posted with a clear question.