Tektronix 465B Faulty Trigger Switches - repair advice required - Page 1
Forum section: electronics / testgear

author: dicky96
author_rank: Regular Contributor
timestamp: July 16, 2019, 10:39:58 am
content: Hi guysUnfortunately my Tektronix 465B oscilloscope has got damaged in transit from the UK to Gran CanariaThe most 'sticky out parts' on the front panel are the little switches in the centre of the Trigger level knobs and these got bent. I couldn't move them or rotate the trigger level controls so I managed to bend them almost back straight again so I could could operate the trigger levels.Now I have a couple of problems. Channel 2 almost works OK. I can sync on trigger OK, but the centre switch that selects + or - edge feels sloppy when I switch it and has no effect. The scope is always triggering on the rising edge.Channel 1 is worse. It will not sync on trigger and both the trigger level and the +/- edge switch will turn all the way round, They kinda 'click' into position at the end of the normal rotation range but then you can turn them again in the same direction.Looking on ebay it seems these scopes are no longer available at almost giveaway prices, a few years ago it seems you couldn't easily sell them (I bought my other analog scope, an LG OS-5020G 20MHz with built in function generator, fully working and good cosmetic condition for just £20 at a radio rally). That doesn't seem to be the case anymore? Anyway I would really like to fix my 458B as I am kinda attached to it - I've had it since 1993 - and prefer to use it over the LG and even my Rigol DS1052e!So is it gonna be simple/easy to fix, and how do I go about it?Rich

author: PaulAm
author_rank: Frequent Contributor
timestamp: July 16, 2019, 01:40:50 pm
content: Those controls are getting hard to find but you should check with Qservice or Sphere and see if they have any in stock. Get the part number from the service manual and do a search; they also show up on ebay when somebody is parting out a scope.I've had more than 1 scope damaged like that in shipment. The front covers are useful to prevent that kind of damage but they never seem to stay with the scope. There should at least be a couple inches of high density foam to protect everything in shipping.

author: Old Printer
author_rank: Frequent Contributor
timestamp: July 16, 2019, 01:49:25 pm
content: What Paul said plus, I would identify the switches/pot you are pretty sure are bad and find the service manual for your scope and get parts numbers. Then check other similar scopes 465, 475 etc and see if the same parts were used in other scopes. When you know what the range of scopes is you can look for a donor. In the US there are a lot of dead or dying 465-475-485 scopes around, the problem is shipping cost. Artek will have the SM if you don't already have it, with a scope that age you will need it eventually.

author: med6753
author_rank: Super Contributor
timestamp: July 16, 2019, 02:41:43 pm
content: If you get in a real bind and can't find replacements in the EU I do have a 465B parts mule that I'm willing to part out but shipping to Spain might get expensive.

author: dicky96
author_rank: Regular Contributor
timestamp: July 16, 2019, 07:03:20 pm
content: Thanks guysI downloaded the manual PDF from elektrotanyaThe faulty switchThe faulty parts are 25 and 26 in the attached pic (figure 2.5) but I can't find the part number in the pages and pages of parts tables as the Acrobat search facility does not work - presumably because the pdf was scanned as an image not a documentChannel 1 - 25 and 26 don't work and feel physically broken insideChannel 2 - 25 does not work (feels physically broken) but 26 is OK and the scope will trigger on rising edge only

author: med6753
author_rank: Super Contributor
timestamp: July 17, 2019, 12:32:45 am
content: From the way you describe it....no Trigger on channel 1, partial Trigger on channel 2 it sounds like your Source switch (27) is broken too. I would check the condition of that switch.

author: dicky96
author_rank: Regular Contributor
timestamp: July 17, 2019, 08:22:47 am
content: Sorry I think I described it wrong. The trigger switches (27) both feel OKTo clarify.....I tried to sync channel 1 triggering on channel 1 - no syncI tried to sync channel 2 triggering on channel 2 - this worked but always on the rising edge - slope switch setting has no effect.I didn't try triggering one channel using the other channel (or anything else) as the trigger sourceI'll try that this morningbest regards.

author: dicky96
author_rank: Regular Contributor
timestamp: July 17, 2019, 11:12:14 am
content: Sorry my error, med6753I can sync on both channel 1 and 2 using either channel as the trigger source - but only on the rising edge regardless of the position of the slope switch which now feels more like a sloppy switch lol.The B dly'd trigger level and slope switches just rotate all the way round with an obvious 'indent' at either end of the normal rotation range. I'm not sure how to use the B trigger unless I read the manual - I never actually needed to use it before. But it needs repairing for sure.I am fairly sure everything else is OK, I just need two of the 25/26 switch assembly from a scrap scope. They should be small and light to post. Are they easy to change , once the covers are off?@PaulYes it is an old scope, I bought it in 1993 at a radio rally but it was second hand then. I guess its from the 80s or even the 1970s!best regardsRichard

author: med6753
author_rank: Super Contributor
timestamp: July 17, 2019, 12:19:59 pm
content: The slope/level switch and pot for both the A trigger and Delayed trigger are standard pot/switch assemblies with wires soldered to them. Once the knobs are removed it's a nut to remove them from the front panel.If you can't get them over there PM me and we'll talk.

author: bd139
author_rank: Super Contributor
timestamp: July 17, 2019, 12:49:52 pm
content: med nudged me on this thread. I have a complete scrap 465 and 475 here. Can probably pull the bits off if you need them and sendPM me if interested.