Trio CS-1830 Oscilloscope

[ITAM805]

hi folks

my neighbour rescued the scope from a skip at work and asked me can I fix it

I fired it up through a lamp limiter and the panel led's came on and the tube lit up - but no trace. Then I tried it direct with the same result. I'm hoping/guessing it's a simple power supply problem, but will need some help as I'm out of my depth with such beasties.

Just found a copy of the service manual so that's a start!

Edit it's actually the operation manual but it has a schematic

Many thanks

[Phil G4SPZ]

It may be working. Many 'scopes blank the trace in the absence of any input to the Y amplifiers. Fiddling with the trigger controls might enable you to see the timebase running

If all stays dark, checking for the presence of EHT would be a start. I'm not familiar with this model, but you could be talking about three or four kV, so be careful!

[ITAM805]

Thanks Phil

happily you were spot on, it works! It needs a serious service both inside and out as you can see. The focusing is a bit vague and touching the sensitivity/timebase controls results in a loss of the trace completely. But at least there's hope!

[KeithsTV]

Phil's right. Many scopes have an Auto/Normal trigger switch. In Auto it will "self" trigger and display a trace but in Manual it will wait for a trigger input before it displays a trace. You will also have to set the trigger level and the channel it triggers from.

Keith

[Phil G4SPZ]

Originally Posted by ITAM805

...The focusing is a bit vague and touching the sensitivity/timebase controls results in a loss of the trace completely...

That's good news then! At least it's working. The symptoms you describe could just be due to dirty tracks on the rotary potentiometers and dirty switch contacts. Careful application of Servisol or similar contact cleaner will hopefully improve matters. The front panel looks very dirty and dusty so I expect that it had lain about for years before going into the skip, not a kind environment for any electronic equipment, so it's bound to require a bit of TLC now!

Good luck with it.

[Restoration73]

Similar to my 33 year old CS-1562 which still works perfectly. To get a continuous display
you need to pull out the trigger knob (Pull Auto) otherwise no display is visible with no input.

[Digger_2008]

Originally Posted by ITAM805

Just found a copy of the service manual so that's a start!
Edit it's actually the operation manual but it has a schematic

Hi,

I have a CS1820 waiting for an SM or schematic to appear. I suspect it is higly similar (same series) to yours. Could you please scan your 1830 schematic and send it to me?

Thanks!

Antonio Falcao
Brazil

[Radio Wrangler]

Just a couple of notes on driving and setting-up scopes:

Focus

There are usually two focus controls; the main, obvious one, and an "Astigmatism" control. This latter one is used to adjust the spot to be circular, but it interacts a lot with the main focus control. Put the scope into X/Y mode and use the X and Y shift controls to put the spot near the centre of the graticule, but off of the lines so you can see it fully. Set the brightness down so it doesn't glare. Alternate between the focus and astigmatism pots, adjusting for the smallest diameter spot. This doesn't always work. If so adjust the focus to get a large spot, adjust astig to get the spot as round as possible (rather than elliptical) then adjust focus for minimum size. Try moving astig a little to one side of this setting and readjust focus. Is the spot now smaller? if so try a bit more in the same direction and repeat until you've found the smallest you can get. If it got a little larger, try going the other way. Once you've done it a few times, it only takes ten seconds. If you haven't got good enough focus now and one pot is at the limits, suspect power supplies and the EHT divider chain. If the pots are in their active zones, then you may have a bad CRT, but check all the voltages before doing anything drastic. You'll need a high voltage probe for your meter.

Alignment:

Set the timebase running to make a line across the centre of the tube, and twiddle "Trace rotation" to get it parallel to the centre line of the graticule.

Triggered Timebases

Up to about 60 years ago, getting a stable trace on a scope was a lot of a fiddly job, and some waveforms you just couldn't sync properly to and you got multiple offset traces or rolling traces. Then Howard Vollum invented the triggered timebase. He first thought of selling it to an existing manufacturer and approached Bill Hewlett and Dave Packard. HP was too busy expanding into new microwave instruments to take on a whole new product area, so Howard was advised to start his own firm, and given guidance on how to do it. He named it 'Tektronix'. So Tek and HP started out as friends.

The triggered timebase does not scan, it sits and waits. Only when a specific trigger condition set by front paned controls happens does the timebase run for one scan only, then it goes back to waiting. The trigger event is a voltage set by a pot (can adjust across positive and negative values) and a direction (positive or negative-going set by a switch) then there are switches to select which channel, to apply AC or DC coupling, to add HF reject or LF reject filters. Until you get these set to suit your waveform - and the waveform has to do something to be able to trigger on, the oscilloscope plays dead.

This is NORMAL behaviour for a triggered timebase. Setting trigger controls blind is a devil of a job when you don't know if or what signal is there. So another switch 'AUTO' got added. It adds a timer. If the timebase hasn't scanned for a while, it fires off one anyway even if there is no trigger. An added wafer on the timebase speed switch sets the timer to suit that setting. So now you can see whether there is anything there, and can see what you're trying to trigger on. AUTO is the usual position for this switch which foxes a lot of people. If you're working with something a bit erratic as signals go, you may not want the auto runs cluttering up what you see, so select NORM and you only see real triggered traces. The picture clears up.

An awful lot of people think the NORM/AUTO switch should normally be set to NORM... and then think a scope is dead. It couldn't have been made more confusing intentionally.

There's one other mystery control; "Holdoff" Use this with NORM on digital or TV waveforms. It's another timer which disables triggering for an adjustable period after a scan. So you can set your timebase to run slowly such as triggering on TV frame rate (HF reject is usually pitched to let frame trigger but not line trigger start scans) and then you can on a posh scope, use a time delay knob - usually 10 turns - to trigger a second (faster) timebase to allow you to look at details within a TV line. The 10 turn delay knob allows you to scroll through line by line. Some TV signals have test waveforms inserted in certain lines during the (TV) blanked period. This is incredible, the first time you get it set up.

So, scopes can easily look dead just due to control settings. You almost have to coax them into giving a visible picture. People who don't know how to drive them often send them for repair or even junk perfectly good machines.

If you want a scope as a user rather than as a vintage exhibit; look for DC amplifiers and a triggered timebase. A dual timebase is nice but not essential.

Don't be scared off by a dual timebase model. Learn the switch and button positions to park the second timebase and use it as a single timebase machine, then when you're comfortable with it, then you can learn what you can do with both timebases active. It's worth learning, sometimes you need it.

Hope this helps a bit,

David

[John_BS]

David:

That's a really good, clear and concise explanation of time-base triggering: you should write a book!

John

[Radio Wrangler]

I did! I got asked to write a chapter for the ARRL Handbook and did the one on oscillators and frequency synthesisers. It's in all editions from 1995 onwards. It contains about as many words as a few detective novels, but a heck of a lot more diagrams

I'd got a lot out of an old (1956 edition) lent to me in the sixties, so the chance to give something back was rather special.

Anyway, I was a bit worried that many posts on here looked like people were being foxed by triggered timebases and I felt that a lot of the confusion was because no-one had ever explained properly what they did and why.

David

[tri-comp]

Hi,
Sorry, didn't notice this post/subject until today.

I have full service-manuals both for the 1820 & for the 1830 in pdf-format.
You're welcome to have copies. PM me with your e-mail addresses

Rgds,

/tri-comp