Hi from Brazil. Looking for advice. - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 07:25:41 pm
content: Thought I should be polite and introduce myself.My name is James and I live in Rio, Brazil.Found this site after listening to an amusing Youtube rant in a car, about cheap USB scopes.Did search for a solution but found nothing.So, I have been offered a cheap Tektronix 2261 analogue scope but it apparently has a problem. It is also 600km's away, which makes hands-on testing impossible and the fella selling it knows little about scopes.When turned on, a single stationary dot appears on the screen without V or H sweep, but whose position can be adjusted via the pots.What I am wondering, is this likely to be a simple - ish repair (dodgy diode, caps, dry joint etc.) or should I just stay well away? Would I be correct in imagining this could be something to do with the horizontal sweep?It is going cheap and here in Brazil scopes don't come cheap and right now i certainly don't have the money to buy anything else even half-decent.Any help would be well appreciated.

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 07:53:51 pm
content: First thought - has he tried to adjust the sweep rate? Tell him to turn the horizontal sec/div knob clockwise a few clicks. It could be in X/Y mode.Other than that, the sweep is buggered. Could be as simple as a cable or chip out of its socket, or much worse.

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 08:02:10 pm
content: Thanks for that,I'd rather not give him hints to get it working coz he'll triple the pricebut what (in your opinion) could be the worst-case scenario possibility?Cheers.

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 08:06:07 pm
content: Quote from: Gazucha on August 05, 2013, 08:02:10 pmYeah, that is a risk. Get a picture of the front panel and look at the knob for yourself, then.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 05, 2013, 08:27:04 pm
content: It looks like you get XY mode when you turn the timebase fully counter clockwise, but it is hard to see:

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 08:41:08 pm
content: Just asked matey and he knows bugger-all about scopes. He bought two to sell on.The photo is unclear and he refuses to take another, but both the channels are set to gnd in the photo.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 05, 2013, 08:45:22 pm
content: Can you show or link to the picture?

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 09:09:33 pm
content: It's the one on the bottom...http://produto.mercadolivre.com.br/MLB-500951095-osciloscopio-com-defeito-_JM#questionTextPrice is about US$100

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 09:15:00 pm
content: here's a clearer image from ebay.. (different scope - same model)

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 09:25:36 pm
content: Another pic of the actual scope.

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 09:37:11 pm
content: Yeah, I can't see fck-all in the picture.

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 09:42:01 pm
content: This is the problem.Which brings us back to what could be the worst scenario?Obviously the best could just be set incorrectly?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 05, 2013, 09:45:32 pm
content: It looks like the timebase is not set at XY mode, it's more like 2 o'clock...

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 09:50:49 pm
content: Quote from: Gazucha on August 05, 2013, 09:42:01 pmLarge hammer to the sweep section. Every custom, expensive hybrid fried. All PCBs except the CRT driver and power supply removed and sold.More likely a loose cable, bad capacitor, or hell, the knob could be spun around and pointing to the wrong spot.It could beanything. How is the price? Might be worth the chance - I'd definitely go for it.

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 10:00:16 pm
content: US$100.But anything decent here will normally cost you $400-500 . . absolute minimum!If you fancy importing, the postage costs a bomb and import duty on ANYTHING electronic is between 60-100%

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 10:07:40 pm
content: Well, that's onlyslightlyextortionate...Here, considering it might be broken, I wouldn't pay more than $25 or $30! But if you say that's a low price where you live, it might be worth it. 20 MHz scopes aren't that complicated, there aren't too many things that could go wrong with it.

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 10:23:43 pm
content: For example, there is a Tektronix 475 on the same site for $550 There's a couple of antiques from the 60's/ early 70's for $200 but most things decent sit around $700.We have sun, beaches and good food, but Brazil is actually still very much a third world country!Thanks for your input.I'm gonna try and knock the price down.

author: Stonent
author_rank: Super Contributor
timestamp: August 05, 2013, 11:42:49 pm
content: Best I can say is flip both channels to GND put it in something other than XY mode and hope there are lines.I got a used scope the other day that I wasn't sure if it was working, the horizontal position was all the way to the left and the trigger was set to max so I couldn't see anything until I messed with those.

author: ivan747
author_rank: Super Contributor
timestamp: August 06, 2013, 01:47:25 am
content: Quote from: Gazucha on August 05, 2013, 08:02:10 pmMake him move the dot into a line and then tell him that is a fault

author: Unknown
author_rank: Unknown
timestamp: August 06, 2013, 02:24:24 am
content: Quote from: Stonent on August 05, 2013, 11:42:49 pmYeah, but as I say, if matey see's this working then he will literally triple the price. He has refused to lower the price...I had actually been hoping someone had experience with a similar 'single dot' on the screen and a possible solution. Ideally with a Tektronix 22xx series.I'm more than happy to solder and replace standard components but don't have much experience working with CRT's.How many of you would risk buying a scope with a single - yet movable - dot on the screen?

author: c4757p
author_rank: Super Contributor
timestamp: August 06, 2013, 02:27:13 am
content: I would, but then, I repair them often. There are many, many things that could make this happen, especially if the seller's being uncooperative and won't help you figure it out. There's a fairly large amount of circuitry between the position controls and the CRT, though, so if they are working I'd say that the majority of the scope is probably working. Do you have anybody nearby who could help you figure it out?

author: Unknown
author_rank: Unknown
timestamp: August 06, 2013, 02:51:00 am
content: No-one nearby no, but I already downloaded and had a look through the Tektronix 2261 service repair manual, which goes into fine detail.By my limited reckoning;1) It turns on and we have a dot on the screen.. so the gun is firing..2) The spot's vertical and horizontal positions can be adjusted via the pots... so it's not totally unresponsive.3) Unless there is some irreparable component on or before the CRT, it should be realistically fixable.In the service manual, one line that caught my eye was something along the lines of 'no dot movement if diode "xyz" had failed' but at the time I was still asking the fella questions, so didn't dwell on it.This is the risk, it could be just a diode or burst cap etc. or could it be the CRT?Then again, do these scopes have a lesser-spotted Lemurian, Polyphase-discombobulator buried in there somewhere? Burned out and irreplaceableI wanna buy a scope, not a door stop!

author: c4757p
author_rank: Super Contributor
timestamp: August 06, 2013, 02:55:09 am
content: Nah, it's not the CRT. It's only got a few functions: horizontal, vertical, blanking, andgoddamn working. Clearly all of those work!Like I said, a 20 MHz scope is a simple device. I haven't seen the schematics, but it's got to be much simpler than my 150 MHz and 400 MHz scopes (which have lots of custom parts). The key is whether or not you have the skills to figure out what is wrong with it. Whatever it is will be easy to fix, though.

author: Unknown
author_rank: Unknown
timestamp: August 06, 2013, 03:41:27 am
content: Cool, that's what I wanted to know...I have 30 years as an electrical engineer, also studied basic electronics at college back in the day and regularly build/experiment with basic power/frequency/radio circuits or repair equipment by replacing standard components.The service manual can be printed out and who knows, maybe its just a dry joint?Very humid in Brazil. You would not believe what happens to our electronic devices!Thanks for the input.Now for the hard part........

author: G7PSK
author_rank: Super Contributor
timestamp: August 06, 2013, 08:02:46 am
content: If you get you can then post pictures here there is sure to be some one to help you, plus we all learn at the same time.

author: Unknown
author_rank: Unknown
timestamp: August 11, 2013, 01:41:04 am
content: Update...After matey with the Tektronix 20Mhz 2261 being unhelpful (and 7 hours drive away), I had the idea to just have a check through the local small-ads and found a fella with a 60Mhz Tektronix 2213A for about the same price (and 1 hour away). This scope had been sitting for almost 3 years.To cut a long story short, when I got there today, we couldn't get any trace unless we pushed 'Beam Find', but that was it. So anyway, I was saying, "no thanks," when he suggested I take it anyway and try to fix it. If I succeeded, then to pay him 'something'.So here I am, with a now working 2213A by my side , but it is not quite 100%.It started functioning after I held the 'Find Beam' for a few (4-5) seconds. It was then left on - with just full screen-width traces for about 20 minutes, until the two running lines went super bright and only appearing just either side of the centre. It was also VERY hot in the high-voltage section so it was left to cool down.It has now been running - out of it's case- with a waveform for well over half an hour, with no recurrence (and much cooler HV section) - and it wasn't necessary to hold 'Find Beam' on startup.The Trigger pot control knob has also been knocked and snapped at some point ( TT p/n 311-2178-00) and this looks like an interesting job, just to get in there to change it, but hopefully I'm wrong.Other than that, I am well chuffed. This bloke will probably accept $30-40. I have already found the pot and now just waiting to see if there is a dry joint somewhere.Any 2213A experience suggestions would be well appreciated.

author: Kremmen
author_rank: Super Contributor
timestamp: August 11, 2013, 01:35:28 pm
content: Oh just pay the man $30 and do what you can with the scope. Even if you ultimately fail to make it work right, the experience would be worth a measly thirty bucks. And as they say - once you are committed, it tends to focus the attention nicely...

author: ivan747
author_rank: Super Contributor
timestamp: August 11, 2013, 01:59:03 pm
content: Congratulations, I consider that a win!Why? Because you are getting *something* for $30 bucks in a country where one of these costs $500. Even it it is not working completely, the worst fix would cost maybe $100, probably. Not $500.

author: Unknown
author_rank: Unknown
timestamp: August 11, 2013, 02:31:11 pm
content: Thanks for the replies.The scope was left on, measuring frequencies, for several hours without any relapse, so I am reckoning that it's not actually brokenand was just playing up after being abandoned so long.Gave it a good clean and it has come up great.Turns out the postage for the potentiometer is 3 times the price of the pot, so I wrote to Tektronix here in Brazil asking if they don't have one laying around. We?l see? (It's a 311-2178-00 if anyone has one?)And seeing as I am looking at a few hours work and perhaps $40 for the part I shall give the man another $40, as he wouldn't care if I told him it was frazzed and that I'd binned it.$40 here, is a lot of money to some people. I wish I could give him more butp.s. reckon working on it with my tongue in the correct position and with one eye closed was the clincher (so thanks Dave).

author: Shock
author_rank: Super Contributor
timestamp: August 11, 2013, 06:23:00 pm
content: burn the dust away with brute force

author: Vorlon
author_rank: Newbie
timestamp: June 27, 2014, 02:10:32 pm
content: Quote from: Gazucha on August 06, 2013, 02:51:00 amWould you please share the link where you downloaded the Tektronix 2261 service repair manual?I need a copy of that manual.Thanks.

author: Unknown
author_rank: Unknown
timestamp: June 27, 2014, 02:46:20 pm
content: Hi Vorlon,been looking for the 2261 manual in my various back-ups but no joy yet. Should be there somewhere.Was there a particular section you wanted to look at?And as for an update to everyone for the original thread, after a good dusting off, warming up and drying out, the 2213A came up a treat (think you say 'Beaut' in Oz) and has been working perfectly ever since.So thank you everyone who contributed earlier in the thread!

author: Vorlon
author_rank: Newbie
timestamp: July 22, 2014, 04:51:20 pm
content: Hi Gazucha,I hope you can find the manual. A friend wants me to repair his scope and I'll need the manual.Thanks.

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2014, 07:50:46 pm
content: Quote from: Gazucha on August 06, 2013, 02:24:24 amThere are a bunch of different things that can cause this and many are repairable but without testing it is not possible to say just from a photo. For instance the horizontal deflection plate leads could be disconnected, the horizontal amplifier could be damaged, or the sweep integrator could be stuck do to leakage or some other problem. Maybe the sweep is not triggered and the blanking in broken.QuoteThe 2 channel Tektronix 22xx series of oscilloscopes include like three different families which are similar enough to share service instructions but it is not clear how this 2261 is related.QuoteI would not unless service documentation is available but I am in the US. Here there are lots of inexpensive alternatives for similar used CRT oscilloscopes.