have I blown up my scope tek 2246 - Page 1
Forum section: electronics / beginners

author: simusix
author_rank: Newbie
timestamp: March 29, 2013, 02:19:02 pm
content: hi group.Im new to this scope stuff, I was trying to measure voltage using voltmeterfuction on scope and no matter how I set scope up I keep getting overv indisplay where voltage should be?......any help appreciated.regards simon

author: GeoffS
author_rank: Unknown
timestamp: March 29, 2013, 02:22:49 pm
content: A few details of what you're trying to measure and how, would help.

author: simusix
author_rank: Newbie
timestamp: March 29, 2013, 02:42:40 pm
content: hi.was following this on u tubeand applying it to my scopeat first it show voltage then I changed a menu to peak to peak reading and and not matter what buttons I press it comes up with -overv or overv,cheers

author: kfitch42
author_rank: Frequent Contributor
timestamp: March 29, 2013, 03:13:19 pm
content: 0) Do you have a multimeter? Try measuring with that to check yourself.1) What are you trying to measure? A 9V battery like in the video?2) You might want to start by shorting the probe (connect ground lead to probe tip) and make sure you get 0V.3) Have you mucked with the volts/div dial on the channel you are using? You probably want to start with the HIGHEST setting and only move lower if needed4) What is the input coupling set to on the channel you are using (usually you can select AC, DC, or GND). You want DC for measuring a battery.

author: simusix
author_rank: Newbie
timestamp: March 29, 2013, 03:30:23 pm
content: hi thanks for your helpI aslso reset back to factory settings0) Do you have a multimeter? Try measuring with that to check yourself...... yes measures 8.2v1) What are you trying to measure? A 9V battery like in the video?......... yes it defelects beam up when connected to battery as video2) You might want to start by shorting the probe (connect ground lead to probe tip) and make sure you get 0V. still reads "overv"3) Have you mucked with the volts/div dial on the channel you are using? You probably want to start with the HIGHEST setting and only move lower if needed........... yes tried that4) What is the input coupling set to on the channel you are using (usually you can select AC, DC, or GND). You want DC for measuring a battery.... set to dc

author: simusix
author_rank: Newbie
timestamp: March 29, 2013, 03:43:57 pm
content: hiscreen look like

author: kfitch42
author_rank: Frequent Contributor
timestamp: March 29, 2013, 05:00:34 pm
content: Google for:tek 2246 operators manualandtek 2246 service manualone of those should have some troubleshooting info. You could also try the TekScopes yahoo group.http://tech.groups.yahoo.com/group/TekScopes/

author: Thor-Arne
author_rank: Unknown
timestamp: March 29, 2013, 07:33:12 pm
content: I think the scope is fine, it surely can handle a 9V battery. My guess is that you have changed some settings either in the menus or with the buttons. Try reading the user guide and use the recalibrate function in the menu.

author: simusix
author_rank: Newbie
timestamp: March 29, 2013, 08:43:28 pm
content: hiread 4 manuals today and there is no reference to "overv" anywhere. I have also carried out a ground test according to manual which shows which buttons must actuated to effect the voltage display test, when i did this display shows overv and a ground symbol next to overv .when i first connect 9v battery the display showed the volts but it now it does not.these sites mention the phrase overvhttp://www.edaboard.com/thread280962.htmlhttp://www.edaboard.com/thread270713.htmlthanks for continued helpregards simon

author: Thor-Arne
author_rank: Unknown
timestamp: March 29, 2013, 09:04:15 pm
content: Hm, is it the same if you use CH2 as measurement channel?I've tried to reproduce this but it works just fine here.

author: simusix
author_rank: Newbie
timestamp: March 29, 2013, 09:30:24 pm
content: higoing to do some logged testing tomorow (sat) and report backthanks for continued helpregards simon

author: Thor-Arne
author_rank: Unknown
timestamp: March 29, 2013, 09:37:23 pm
content: Do that.Also, check that the relays is responding when you push the coupling buttons.

author: simusix
author_rank: Newbie
timestamp: March 30, 2013, 12:32:18 am
content: hiI just bought this off ebay and came through the post, was well packaged, I was thinking maybe some componant/chip has come loose? i first powered it up for 1/2 hour measured the9v battery voltage and worked ok then came to measure a 1.5v battery thats when it stopped displaying voltageregards simon

author: Thor-Arne
author_rank: Unknown
timestamp: March 30, 2013, 01:30:39 am
content: It might be something has come loose or a relay being stuck, this is why I asked if you had tried another channel for the measurement.My guess is that if it is, it's probably something very close to the input since it otherwise would catch it in the self test.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 30, 2013, 04:44:59 am
content: Does the trace deflection correspond to around 8.2V?If,for instance,you have the 'scope volts/div set to 2V/div with the instrument set to DC input,you should see a deflection of just over4 divisions.I am not familiar with the 2246---are you sure that it will directly read the input voltage,or do you have to set some cursors to line up with the minimum & maximum of your deflection?

author: rf-loop
author_rank: Super Contributor
timestamp: March 30, 2013, 06:35:23 am
content: It have automatic measurements. I do not remember exactly if 2246 have also gated measurements but 2246A have.---------------For OP:If suspect inputs fails it need carefully look all voltage ranges (as described in serv manual) with enough good test generator. Yes for field quick check even battery can use.. and also of course scope own probe adjustment output.There need switch between V/div settings and watch carefully that always display is stable without drop outs / drifts. When relays go bad they may give very "fun" results.(specially watch these steps where attenuator/amplifier change relays position... this "truth table" is in serv manual)CH1 and CH2 both have 5 relays in input attenuator/amplifier circuit. These relays contacts may go bad. Not serviceable with any "contact spray trick". They need change if they are bad. And it need lot of work. But it can do.Very rare is relay driver array fail. Relays contact problem is more common after years of hard use.Also, selfcal do not always know relay is fail and then it may show very strange vertical levels.If internal adjustments are very badly out of order this automatic measurement do not work and may give what ever results also overv.1st suspect. Input relays!If trouble shoot this scope so that really want do some useful and not only hanging around there need Tektronix service manual.There is also very very good deep explanation how every circuit work. (Theory of operation).There is described test procedures and full detailed adjusting procedure (what really need follow tightly. There is not jokes, it just need follow exactly and if can not go over one step ok then need stop and repair problem and then start all agen.)When these scopes (2246, 2246A, 2247A etc) is in good condition they are really good and reliable professional analog oscilloscopes. They are far far over 2213/2215 "simple machines".2246-2247 fan is other case. And there can not reduce airflow for reduce noise. There can install better fan and isolate it from chassis. But airflow need be as original. And never install cheap entertainment device fan. One time fan fails you perhaps can pick-up scope to recycle or salvage some spare parts. (but this model thermal design is not so critical as 24xx models what can not run safe with case opened without external service fan)Power supply is also "weak". Some capacitors may fail after 20 years of use.1. Read user manual2. Read service manualbeforeopen it and never start adjust any internal adjustment before exactly know what it is and how it need adjust. This is much more complex unit than it looks like.Note: there is many differen versions and oldest 2246 may differ lot of.Also note this:

author: simusix
author_rank: Newbie
timestamp: March 30, 2013, 12:50:47 pm
content: hi peepsswitched on this mornlet it warm up for 30 minsoverv still shows after 30 minscarried out out all self tests and voltage calibrations (did all this yesterday as well....spent five hours playing with settings and buttons!!)overv not showing nowcarreid out performance ch1/2 voltmeter check ..(says check ground readout is +- 1.25 mv it is 0.00v on my scopeset chan 1 to 5v on volts/div and 2secs on vert/divthe trace dot moves from left to right slowlypreeded voltmeter button and set to dc on chan 1connected 9v battery to chan 1 it deflects up just under 2 divisions on screen (it deflected yesterday even when it showed "OVERV")it now shows correct voltage 8.3v on display (measured with mulitimeter as well 8.3v)carried out same procedure on chan 2 and all works ok.....butthe voltage wanders up to 10.5 volts and comes down to 8.v ..... does this a few times then settles on 8.3v (multimeter still reads 8.3v)also tried voltage reading on 1kHz 2v p-p square wave and voltage wanders about before settlinghave turned it off and over last half hours and stilll doing above but no OVERVas I,m typing this there is nothing connectted to scope its still in voltage measuring mode and voltage is fluctuating up to 10 volts on its own.if I touch probe to ground it pulls voltage down from where its wandered to (10.5) down to 0.00does not fill me with measuring confidencecheers simon

author: simusix
author_rank: Newbie
timestamp: March 30, 2013, 01:02:01 pm
content: hianother guy from another chat board has sent me thisYour second Edaboard reference is the answer to your problem. You need a servicemanual, look at the vertical inputs schematic. The scope is not getting itsvoltage reference so it can't calibrate. You either have the voltage reference(volt cal) signal missing (unusual),a bad relay K101 (common) or bad relaydriver chip U174, (fairly common). These are references to CH1, same applies toCH2. Depending on your ability with electronics. soldering etc, these are noteasy to service for beginners.I have a 2246a full service manual but not a 2246 manual is there a lot of difference?cheers simon

author: M0BSW
author_rank: Frequent Contributor
timestamp: March 31, 2013, 09:13:59 am
content: You should really send a message to W2AEW Alan on here he is the Tektronix Wizard

author: priya942
author_rank: Newbie
timestamp: October 30, 2013, 01:37:15 pm
content: I have an identical issue that remains unresolved after checking and re-checking everything. Same symptoms: signal gain drifts on Ch2, voltage measurement shows OVERV or -OVERV, but everything else works perfect. Tested the self cal signal and it is fine, relays are fine, replaced a bad U174 relay driver that literally caught fire and took the scope power supply with it.I think it is related to the hybrids that there is no easy repair for. I have thought about building a replacement hybrid daughter board with discrete components, but then decided that it was too much work.have you been able to resolve this and if so, what was the culprit?Thanks,Priya.

author: rexxar
author_rank: Frequent Contributor
timestamp: October 30, 2013, 04:24:37 pm
content: Have you looked at the service manual yet? It has a troubleshooting guide on page 6-5.Here's a link.The first rule of troubleshooting is "thou shalt check voltages". Check the power supply, then any local regulators you can find. If the power supply went way over voltage when it died, it could have taken all the local regulators with it.