Oscilloscope probes to test standard plug outputs? - Page 1
Forum section: electronics / beginners

author: gjames
author_rank: Contributor
timestamp: August 22, 2022, 08:38:00 pm
content: I've tried to do a search but haven't found anything on this subject. So if I'm opening up something already discussed, please give me the reference and I apologize in advance.I'd like to use my oscilloscope to display signals coming out of analog synthesizer modules or other audio devices. The plugs could be banana, TRS, RCA, XLR, etc. I suppose I could just make plugs with exposed wires and use clips, but I'm worried that might wreak too much havoc on the probe's signal. I've been searching the net for probe tips using these plugs and the only ones I'm running across are for meters, not scopes.So, can anybody lend some advice or assistance here? Am I thinking like a newbie, should know better and just do it?Greg

author: inse
author_rank: Super Contributor
timestamp: August 22, 2022, 08:43:47 pm
content: For audio frequency, almost everything is allowed.Buy some BNC cables of double length, cut them in half and attach whatever you like.Just be careful if you want to watch more than one signal source, you might create ground loops.Amplifier outputs may not share a common ground, so probing both channels can create a short circuit.

author: ataradov
author_rank: Super Contributor
timestamp: August 22, 2022, 08:50:04 pm
content: The only ones that are readily available from your list is RCA. Their pinout is obvious and I think they are primarily designed for video surveillance systems. A lot of those strange adapters come from this area.For TRS there is no obvious pinout and XLR is far too marginal for existing solutions to exist.You don't need to have exposed wires, you can just make custom adapters with short lengths of connecting wire. This is probably the most optimal way of doing it.

author: SmallCog
author_rank: Frequent Contributor
timestamp: August 22, 2022, 09:51:15 pm
content: I'd choose a "standard" audio connector as an intermediary such as an RCA so you only need a BNC to RCA adaptor leadThere are countless audio adaptors available to convert between different connections. Use these to turn your XLR's or whatever into RCA's, then from RCA to your scope

author: gjames
author_rank: Contributor
timestamp: August 22, 2022, 10:26:30 pm
content: Thanks folks. This is basically what I thought in lieu of manufactured probe tips. So I get to do some more soldering!!!BTW: I have a Tek 2465B that's just been calibrated and I'm really excited to use this classic.Greg

author: tggzzz
author_rank: Super Contributor
timestamp: August 22, 2022, 10:37:54 pm
content: Quote from: gjames on August 22, 2022, 10:26:30 pmEnjoy using it, but beware of two weaknesses: the RIFA capacitors and the battery in the non-volatile RAM that contains the calibration constants. The original batteries had a lifetime of 10-15years; you can do the arithmetic.

author: gjames
author_rank: Contributor
timestamp: August 23, 2022, 02:07:59 am
content: Thanks for that. I've found a lot of info covering what you mention on this wonderful site (and you're in there too!):EEVblog #1203 - REPAIR: Tektronix 2465B Oscilloscope (YouTube)eevblog.com/forum/repair/tektronix-2465b-repaireevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown (This thread alone has been active for 4 years!).And quite a bit also on the Net.Several years ago ("BP" - Before Pandemic) I purchased a "survival kit" of components, including a couple of the the EPROMS. I actually have 2 scopes. So one can be in surgery while the other one works on the bench in the waiting room.Caps and RAM are definitely on my priority list.This site and all the contributors like you are making my retirement hobby much more enjoyable. Thank you.Greg

author: vk6zgo
author_rank: Super Contributor
timestamp: August 23, 2022, 03:17:53 am
content: Quote from: gjames on August 22, 2022, 08:38:00 pmIdeally, XLR are balanced, so you could, if you want to maintain balance, make a lead with two BNCs, one for each leg, with the outer part of the coax connector returned to the cable shield, & use two channels in the "poor man's differential" setup.Often, people don't bother, though.RCA to BNC adaptors are common, not so much TRS or banana plugs.There are plenty of cheapo BNC to alligator clip leads around---you could just ditch the alligators & replace them with banana plugs or whatever.If you are looking at something which expects a 600termination this complicates things, as they aren't a standard BNC terminator, so you would probably have to make one if you are fussy about setting the "correct voltage".A lot of more modern designs have very low output impedance, so will present "near as dammit" the same voltage to a 600as to much higher loads.

author: tggzzz
author_rank: Super Contributor
timestamp: August 23, 2022, 08:33:08 am
content: Quote from: gjames on August 23, 2022, 02:07:59 amAlsohttps://groups.io/g/TekScopesBe careful of the date of manufacture. Questionable whether it is worth replacing a 35yo battery with a 30yo battery! Also beware of outright fakes. Best technique is to copy the contents to somewhere safe, so you can "reuse" them in a completely different implementation. At the very least point make a video of the screen as you use the test routine to scroll through the contents.

author: gjames
author_rank: Contributor
timestamp: August 23, 2022, 03:00:25 pm
content: I bought all the parts from Digikey, so I hope there are no fakes.Greg

author: gjames
author_rank: Contributor
timestamp: August 23, 2022, 04:29:08 pm
content: "At the very least point make a video of the screen as you use the test routine to scroll through the contents."They were calibrated by Trescal. I live about 10 minutes from their facility, so its extremely convenient and I don't have to ship anything. They have a long-time Tech that loves to work on older equipment and it seems there are a fair number of people here that still have and use older gear.When I had the scopes calibrated (just last month) I got printouts of the calibration data. Is this sufficient?Also, I'm going to look closely at the EPROMs to see when they were manufactured. I'll let you know what I find.Thanks to everyone who's replied. All the comments are helpful.Greg

author: gjames
author_rank: Contributor
timestamp: August 23, 2022, 06:52:56 pm
content: The SRAMs I have are Dallas DS1225AD 1548D4 408585 from Digikey. They have never been used.

author: Robert763
author_rank: Super Contributor
timestamp: August 23, 2022, 07:46:04 pm
content: For BNC's most 'scope probes come with an adaptor. It's just a simple metal tube with slits in it. It fits on the ground part of the pobe tip and then goes into a BNC socket. The probe tip goes directly into the BNC center contact.

author: tggzzz
author_rank: Super Contributor
timestamp: August 23, 2022, 10:55:42 pm
content: Quote from: gjames on August 23, 2022, 04:29:08 pmNo idea!But then I've no idea how the crude screen dump relates to the contents of the RAM, only that if the "before" and "after" screen dumps are the same then the cal should have been transferred. I won't bother to try to figure that out until after I've had a problem, and then there will probably be a lot of "research" and/or trial and error.

author: gjames
author_rank: Contributor
timestamp: August 24, 2022, 06:26:57 pm
content: Your original suggestion to back them up is the most logical and surefire solution. So down that rabbit hole I go!.Greg