Farnell analogue oscilloscope timebase issue - UK Vintage Radio Repair and Restoration Discussion Forum

mpegjohn · 23rd May 2018, 12:31 pm

Dear all,
Last night my trusty Farnell 2 channel analogue oscilloscope decided not to be trusty anymore.
I just get a dot in the middle of the screen, and it does not scan. So I am guessing that the timebase is not running anymore.

The thing cost me £50 off ebay about 7 years ago, so I can't complain.
I just thought I would ask if anyone has ever fixed one of these with this problem, and if it is a simple fix.

It is a solid state thingy.

I don't have the model number with me, but when I get home tonight I will post it.

Thanks,
John.

Argus25 · 23rd May 2018, 11:58 pm

Most scopes have an X-Y mode that switches off the timebase, sometimes its selected when rotating the timebase control anticlockwise and sometimes with another switch too. If the scope was working when you put it away last and now its not, it is possible it is just oxidised switch contacts. Try exercising the switches that put it into X-Y mode.

However, especially if it failed on the fly, it could be any other number of failures in the power supply to the X amplifiers or the timebase or a component failure in there. If that is the case, you will need the manual/schematic to fix it most likely. A clue would be if the Y amp was still working, most likely then the power supply (that is probably common to the X and Y output amp) is ok.

It pays to have the manual and schematic for every piece of test equipment in a workshop as one day they always come in handy. It reminds me of a sage remark from a workshop owner I knew; I asked about a piece of equipment there and said; "have you got the manual ?" he replied; "I never get into bed with any equipment without the manual"

Sometimes people wait for an item of gear to fail before they attempt to get the service manual or schematics, but it is better the other way around.

sentinel040 · 25th May 2018, 5:41 pm

When working for a large provincial newspaper we had a small Farnel scope in the “stretchmaster” length control panel for the pre-print colour unit and it blew up the time base output transistors a few times. I think you need the manual, unless you fancy a bit of poke and hope. Good luck.

Regards
Ian

Diabolical Artificer · 26th May 2018, 6:56 am

What model is it? I have a manual for a couple of Farnell scopes.

Andy.

23rd May 2018, 12:31 pm	#1
mpegjohn Hexode Join Date: Aug 2013 Location: Chichester, West Sussex, UK. Posts: 270	Farnell analogue oscilloscope timebase issue Dear all, Last night my trusty Farnell 2 channel analogue oscilloscope decided not to be trusty anymore. I just get a dot in the middle of the screen, and it does not scan. So I am guessing that the timebase is not running anymore. The thing cost me £50 off ebay about 7 years ago, so I can't complain. I just thought I would ask if anyone has ever fixed one of these with this problem, and if it is a simple fix. It is a solid state thingy. I don't have the model number with me, but when I get home tonight I will post it. Thanks, John.

23rd May 2018, 11:58 pm	#2
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Farnell analogue oscilloscope timebase issue Most scopes have an X-Y mode that switches off the timebase, sometimes its selected when rotating the timebase control anticlockwise and sometimes with another switch too. If the scope was working when you put it away last and now its not, it is possible it is just oxidised switch contacts. Try exercising the switches that put it into X-Y mode. However, especially if it failed on the fly, it could be any other number of failures in the power supply to the X amplifiers or the timebase or a component failure in there. If that is the case, you will need the manual/schematic to fix it most likely. A clue would be if the Y amp was still working, most likely then the power supply (that is probably common to the X and Y output amp) is ok. It pays to have the manual and schematic for every piece of test equipment in a workshop as one day they always come in handy. It reminds me of a sage remark from a workshop owner I knew; I asked about a piece of equipment there and said; "have you got the manual ?" he replied; "I never get into bed with any equipment without the manual" Sometimes people wait for an item of gear to fail before they attempt to get the service manual or schematics, but it is better the other way around.

25th May 2018, 5:41 pm	#3
sentinel040 Hexode Join Date: Feb 2007 Location: Near Lichfield, Staffordshire, UK, most of the time and Crystal Palace, S London, some of the time.. Posts: 330	Re: Farnell analogue oscilloscope timebase issue When working for a large provincial newspaper we had a small Farnel scope in the “stretchmaster” length control panel for the pre-print colour unit and it blew up the time base output transistors a few times. I think you need the manual, unless you fancy a bit of poke and hope. Good luck. Regards Ian

26th May 2018, 6:56 am	#4
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Farnell analogue oscilloscope timebase issue What model is it? I have a manual for a couple of Farnell scopes. Andy. __________________ Curiosity hasn't killed this cat...so far.