Tektronix 465B oscilloscope repair - Page 1
Forum section: electronics / repair

author: RetEngr75
author_rank: Newbie
timestamp: November 21, 2016, 09:55:05 pm
content: I just bought this unit on Ebay. I opened and read the manual about checking voltage and settings before powering up.I used oscilloscopes before but not this particular one. After the background read, I plugged it in.It came up with one horizontal line raster. I began to look at the controls for the 2nd channel and it went out,shut off no lights any where. I pulled the plug and checked the main 1 1/2 fuse and it was open.I then bought replacement fuses marked 1.5 amp but they opened as soon as I powered up.I tried a 2A fuse and it came up and I quickly shut it down hoping not to cause further damage.I am at a loss for the next step and appreciate any suggestions even repair locations near Bethlehem Pa.Rich

author: tggzzz
author_rank: Super Contributor
timestamp: November 21, 2016, 10:28:53 pm
content: Posting the same message in multiple places is bad etiquette. It can cause people to waste their time duplicating what other people have written.

author: David Hess
author_rank: Super Contributor
timestamp: November 22, 2016, 12:14:51 am
content: It might be a shorted solid tantalum capacitor however the fact that it blows the power line AC fuse probably indicates a more serious problem like a shorted rectifier in the power supply which may itself indicate a shorted input capacitor.

author: dan3460
author_rank: Frequent Contributor
timestamp: November 22, 2016, 01:37:44 am
content: +1, I have a couple of 465s. The power supply is probably the same. All of the ones that I have repaired, including the one that I have on my bench have had bad power capacitors.This old capacitors are big cans with several tabs for ground, the problem is that new caps are much smaller that the old ones and putting them back on the board is awkward as you need to make sure that you ground all the holes around each cap.In a forum, don't remember if this one or other, a member had made round circuit boards to mount the caps so it becomes really easy to mount them keeping all the holes grounded. Here is a picture of what I did. I still have some of the disks, I will order more in the future, I know that I have the gerbers somewhere if you want to order them.

author: David Hess
author_rank: Super Contributor
timestamp: November 22, 2016, 06:37:00 am
content: Those adapters for the metal can pinout are pretty slick but if I can get away with it, I just use radial or snap in capacitors and modify the board if necessary.One trick you can use if it will be convenient for the replacement capacitor to be the same diameter is to actually select it by diameter. As dan3460 points out however, modern capacitors have much better volumetric efficiency but this can somewhat be made up for by selecting a higher voltage capacitor than strictly necessary and this also has the advantage of yielding a higher ripple current rating although this is seldom needed with input capacitors.The included photograph shows where I did this and also the size difference between old can capacitors and modern capacitors.RetEngr75, given the symptoms you have and even though it will be a lot of work, I would at least check all of the input rectifiers and input capacitors for shorts. Both have been known to fail in the 465 series of oscilloscopes. A variac would be handy for testing at low line voltages.