Trace disappeared from scope

[windmill john]

Okay, this should probably be under beginners as I am and chances are I doubt with my beginner level, I’ll go in the scope, but as above, trace has disappeared.

Leader 1021, just purchased.
Last week, I was following a basic know your scope video.
I had the trace for a comfortable 10 to 15 minutes and then it went, as in it slowly faded out over about 5 to 10 seconds.
I’m pretty sure it’s not a setting as I was following the video, tweaking the square wave testing the probes.

I wasn’t happy with the probes as one was cracked and the innards were showing, so I turned off the scope, ordered some new leads and have just tried again; still no trace.

To add……….. there was a bit of burning smell this second time…….. now I judged the smell as not a serious smell,  it it wasn’t there the first time. My wife came in and said what’s that burning; there’s your benchmark….

Anyway, not totally sure why I posted as I’m too new to fix this I think. But posted in case someone said oh yes, this model normally has……

Depending what comes back, then I’ll either see if I can find someone local for a repair quote or bin…. As it’s a CRT, not too keen on fiddling, even if I have discharged it etc. Shame, as it looks a good scope and has invert for the second channel, which I’d read about with regards to a safety video.


Thanks all.

[807]

You have probably already tried this, but have you tried connecting the CAL output to CH2 to see if it's just a CH1 problem?

[AndyBeez]

The sync is set to TV-Horizontal - not sure if that will trigger when fed a 1Khz square wave on this vintage scope? For elimination, try coupling with DC. Otherwise power off and leave to cool down, see if the beam comes back.

[tggzzz]

Leader 1021, just purchased.
...
and then it went, as in it slowly faded out over about 5 to 10 seconds.
...
To add……….. there was a bit of burning smell this second time…….

Open it up and look carefully at each component - especially electrolytic and RIFA capacitors.

Measure the PSU voltages and ripple.

Given there's a dent on the case, perhaps the tube is fractured, letting the air in. If the dent wasn't visible before purchase, complain to the seller.

Keep your fingers away from the kV around the tube.

[wasedadoc]

Set the trigger mode to 'Auto'.

There is no need to connect the probe's earth clip when connecting the tip to the CAL signal.

[windmill john]

Thanks all.

I did try channel 2.

When I switched triggering to DC, I did get two dotted traces moving right to left approx 1 CM apart. When they arrived on the left, I then only got a large glow half off left of screen. Glow was about 3 to 4 CM across.
Fiddling with position I could move the glow up and down only, no other settings had any effect.
After a minute-ish, the trace disappeared.

Out of my depth now. I might take a look inside for obvious issues, caps etc and also ensure I discharge the tube first.

The dent was there in the photos when I bought it. It must have taken a lot of force. If nothing is obvious and I cannot find a local fixer, it may just be an art piece…

[Andy Watson]

If nothing is obvious and I cannot find a local fixer, it may just be an art piece…

Here is a link to poor but legible scan of the service manual.
https://www.opweb.de/english/company/Leader/1021
Whilst most of us have probably learnt our trade by making mistakes, inside an oscilloscope is not the best place to start! Take care.

Where is local? There may be some local help available.

[james_s]

If the trace gradually faded out then it's definitely an internal problem, probably a bad resistor or capacitor, possibly a solder joint or other loose connection. You (or somebody) are going to have to get inside it and have a look.

[tggzzz]

Was it purchased as "working" or not? If working, complain to the seller.

What is its provenance in terms of the previous user, when it last worked, where it was stored?

When I switched triggering to DC, I did get two dotted traces moving

So, the tube isn't the main problem.

right to left approx 1 CM apart. When they arrived on the left, I then only got a large glow half off left of screen. Glow was about 3 to 4 CM across.

There is life in the x-deflection circuit.

First debug the power supplies. Without that you will be chasing your tail.

Was the trace speed related to or changeably by the time/div control? If so then moving in the wrong direction is strange.

Fiddling with position I could move the glow up and down only, no other settings had any effect.

There is life in the y-deflection circuit and the input amplifiers.

After a minute-ish, the trace disappeared.

Is that a second time or what happened the first time you turned it on?

Out of my depth now. I might take a look inside for obvious issues, caps etc and also ensure I discharge the tube first.

Depending on the circuit/tube, that can be non-trivial.

Make sure you know where the kV is to be found on the schematic, PCBs, other components - and keep your fingers away.

The dent was there in the photos when I bought it. It must have taken a lot of force. If nothing is obvious and I cannot find a local fixer, it may just be an art piece…

While renovating old scopes can be fun and rewarding, it sounds like - as someone that has never used a scope - you will be struggling to understand what it ought to be doing.

If that's the case, then you probably won't be able to do much more than a careful visual inspection and checking the power supplies.

[AndyBeez]

From your description, the prognosis is not so good. Not sure if the other guys agree, but I suspect something in the HT power supply, maybe even the HT transformer. The burning smell is always a red flag. This could just have been an incinerated insect, otherwise I might suspect a high voltage resistor, transistor or diode gone fizz. It's kinda working, but you'll need to ask your misses if she's taken out life insurance before you poke your fingers inside. You can always post internal photos here for an autopsy. I agree with @tggzzz - if this is unfamiliar territory, put this down to experience, and find another scope. Plenty of decent analog Hameg and Tektronix scopes on eBay for around the £150 mark. Petition the guys on the test equipment thread for their options! Try and buy from a fellow EE, rather than a seller who describes the scope as "working". Avoid dents

[tggzzz]

From your description, the prognosis is not so good. Not sure if the other guys agree, but I suspect something in the HT power supply, maybe even the HT transformer. The burning smell is always a red flag. This could just have been an incinerated insect, otherwise I might suspect a high voltage resistor, transistor or diode gone fizz. It's kinda working, but you'll need to ask your misses if she's taken out life insurance before you poke your fingers inside. You can always post internal photos here for an autopsy. I agree with @tggzzz - if this is unfamiliar territory, put this down to experience, and find another scope. Plenty of decent analog Hameg and Tektronix scopes on eBay for around the £150 mark. Petition the guys on the test equipment thread for their options! Try and buy from a fellow EE, rather than a seller who describes the scope as "working". Avoid dents

A rule of thumb for a working old analogue scope is £1/MHz.

Ignore any scope where you can't see a trace, and preferably see the cal out waveform or better.

If the OP is in the SW, I have several decent scopes I ought to sell 

[windmill john]

First let me say a big thanks to all contributors.

I am virtually brand new to electronics. Not a wuss, but always read of dangers first.
So, given the fact that I’ve never really circuit tested something more serious than my motorcycle’s wiring, I’ve decided not to delve inside.

Given the number of articles I’ve read of implosions, even though this isn’t a 60s tube and the more important fact that the top has had a serious belt, I’m staying away.

My fault for buying virtually the cheapest one on eBay. Yes the previous owner covered himself with the normal line: “I don’t know much about them but it turns on and I can see a line”….. caveat emptor……

I’ll close this off. I’ll carry on learning, but stay away from CRTs and try some simpler things first!

[james_s]

The risk of implosions is effectively zero, unless you remove the CRT from its protective housing and smack it with a hammer it is not going to harm you. CRTs made in the last 50 years or so all have integral implosion protection and a typical scope tube is far smaller than a TV tube and usually completely enclosed in a metal shroud to shield it from interference. There is some risk of electric shock, but that is pretty trivial to avoid. If you are really nervous, unplug the scope and let it sit for a few days, at that point everything will have fully discharged and it is safe for even a novice to poke around inside.

[Gyro]

From your description, the prognosis is not so good. Not sure if the other guys agree, but I suspect something in the HT power supply, maybe even the HT transformer. The burning smell is always a red flag. This could just have been an incinerated insect, otherwise I might suspect a high voltage resistor, transistor or diode gone fizz. It's kinda working, but you'll need to ask your misses if she's taken out life insurance before you poke your fingers inside. You can always post internal photos here for an autopsy. I agree with @tggzzz - if this is unfamiliar territory, put this down to experience, and find another scope. Plenty of decent analog Hameg and Tektronix scopes on eBay for around the £150 mark. Petition the guys on the test equipment thread for their options! Try and buy from a fellow EE, rather than a seller who describes the scope as "working". Avoid dents

I certainly wouldn't give up on that scope yet. Those old Leaders are nice little scopes - clearly not in the Tek league, but they also don't suffer from the problem of custom parts, in-house part numbers, or bleeding edge analogue technology. Just good basic engineering. I doubt the problem has anything to do with the dent (in fact it's a testament to the build quality that the tube is still intact). Just read and thoroughly understand the steps in the service manual before proceeding with appropriate caution.

Jim Williams used to say that there were few better ways of learning stuff than from fixing test equipment.

[tggzzz]

My fault for buying virtually the cheapest one on eBay. Yes the previous owner covered himself with the normal line: “I don’t know much about them but it turns on and I can see a line”….. caveat emptor……

That phrase is irrelevant on fleabay! What matters is the "condition" field:
"Used" => it works as designed, and fleabay will support your claim
"For spares and repairs" => caveat emptor. I use this to describe the stuff I have flogged, but I also show many pictures of something operating normally, see attached photos.
Fleabay really needs a category "works well enough to be used, but some values may have drifted out of spec over the decades, so don't be a twat".

N.B. CRTs aren't the issue per se. I've bought and sold good things with CRTs on fleabay. Correct packing is important!

Best thing is to see the scope working, and fiddle with the controls. That means you can pay cash, avoid packing and shipping fees, avoid shipping damage, and check it.

BTW. Don't forget to include the cost of probes of the type relevant to how you are going to use it safely. FFI see https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

[windmill john]

Dog with a bone.... Too early to give up!...

I opened him up and the circuit board is very clean. As can be seen from the dust, this was either used upright, or stored that way for a long time.

Now, the biggest, ONLY...... worry for me is safety. It's been off 24 hours. Having read many things, bearing in mind it's has been off 24 hours. What might hold charge? I cannot see the anode. As some places say it might be underneath the tube. Can I discharge it some other way? I'm aware of making a discharge tool etc, just need to know where to stay away from.

The 'Danger, high voltage' sticker. Does that apply when off too?

In other words, if not connected, is there anything I should stay away from? Yes I'm new, but want to play safe obviously.

I have had two shocks in my life. One threw me across a lift and the other was touching a flash capacitor in a disposable camera. That gave me Six Million Dollar Man hearing for the next 15 minutes! I'd rather not suffer either again.



Thanks

[pcprogrammer]

Dog with a bone.... Too early to give up!...

  I know the feeling 

I opened him up and the circuit board is very clean. As can be seen from the dust, this was either used upright, or stored that way for a long time.

Most likely stored upright.

Now, the biggest, ONLY...... worry for me is safety. It's been off 24 hours. Having read many things, bearing in mind it's has been off 24 hours. What might hold charge? I cannot see the anode. As some places say it might be underneath the tube. Can I discharge it some other way? I'm aware of making a discharge tool etc, just need to know where to stay away from.

The 'Danger, high voltage' sticker. Does that apply when off too?

In other words, if not connected, is there anything I should stay away from? Yes I'm new, but want to play safe obviously.

When the power is of you only have to worry about residual charge on the tube itself. I think the connection is underneath the tube. There is a extra insulated wire running from the metal "high voltage" box in that direction, but it is not to clear on the picture.

The high voltage transformer is most likely in the metal box.

Can you post pictures from underneath, if that cover can be removed of course.

I have had two shocks in my life. One threw me across a lift and the other was touching a flash capacitor in a disposable camera. That gave me Six Million Dollar Man hearing for the next 15 minutes! I'd rather not suffer either again.

  I can relate to that. Had my fair share of shocks, but only once from a color tv tube. Luckily jumped across some plastic, but still hurt like hell.

[windmill john]

Thanks. It’s going to be tomorrow now before I can get the cover off, but I’ll post a picture when done.

[Bud]

Surely you start off by cleaning the dust off. The burning smell may had come from the dust burning on the CRT. Also plan to carefully unplug, contact clean and reseat all connectors. The one on the CRT back too.

[free_electron]

-cough- - hack- -cough cough- , remove the dust bunnies -cough-.

i'm having an asthma attach just looking at the pictures...
that's most likely where the smell came from...

[james_s]

I don't see any large capacitors in there so yeah, pretty much just the tube itself and it's *probably* fully discharged by now but it's always prudent to treat it as though it's charged, don't touch the anode connection unless you have to. A tube of that size is not going to hold all that much of a charge anyway, I've been zapped by CRTs a handful of times and it's like a large static electricity shock when you touch a doorknob or something on a dry winter day, it's annoying but not nearly as painful as a mains voltage shock which is much lower voltage but has a lot more current behind it.

I'm surprised that the tube is exposed to the degree that it is, do be careful not to strike the funnel with anything, it's thick glass there's no reason to tempt fate.

[Gyro]

Being a 20MHz scope, the acceleration voltage is 'only' 2kV. This will limit the amount of stored energy in the CRT relative to the ~20kV of high performance scopes. The cathode and grid etc. are biased negative by 1900V like most scopes (beware), but there won't be a final anode cap or PDA. [Edit there isn't even an external aquadag coating on the tube bell to act as an EHT capacitor plate with the internal coating, so the CRT itself isn't really capable of storing any charge].

It would be good to see a photo of the PSU PCB on the bottom side of the case. A burning smell hopefully translates to something looking burnt. The isolated CRT filament and HT voltages are all driven from transformer T601 and all voltage multiplier parts are discrete, so unless T601 itself is fried, there's nothing that can't be fixed. It could be one of the multiplier diodes or capacitors shorted, but at this stage, it could equally be something as simple as a shorted bridge rectifier or the PSU PCB.

Most troubleshooting can probably done with the scope cold and a methodical search for shorted parts, starting in those areas. It would also be worth re-seating the connectors on the TO220 transistors / regulators on the dusty rear panel, which could definitely do with a vacuum (preferably with the aid of an air blower and a soft brush).

...
I'm surprised that the tube is exposed to the degree that it is, do be careful not to strike the funnel with anything, it's thick glass there's no reason to tempt fate.

With a low voltage tube like that, there isn't as much need for the bell to be screened. Magnetic shielding is limited to the tube neck. Likewise there is no need for side pins for the deflection plates. Everything can go in through the tube base PCB (Y plates on the white (old 300R antenna feeder cable) ribbon.

[windmill john]

Thanks all. Don’t worry, the dust will be banished.

Gyro, James, just to clarify, as tomorrow will be at least 48 hours cold, am I “totally” safe?
If it’s just the anode, can I discharge that?

Re cleaning, can I clean/remove all connectors at the rear safely?

[Gyro]

I would say, yes, you are safe, but caution should always prevail! Check all capacitors, at least any that are marked above [Edit: 1kV ok, let's make it 400V] in the parts list with a DMM on voltage setting. They are all low value ceramics though, so even the act of measuring them will discharge them if they aren't already. The CRT used on that scope has no inherent charge storage mechanism (no 'glass capacitor' made up of inner and outer coatings).

Yes, with the scope cold, there is no problem with removing the rear panel connectors (other than forgetting their position and orientation!). It does make the parts very easy to replace if faulty.

Again, pay very close attention to the service manual, block diagram and schematic. As I mentioned above, you can probably pretty much achieeve your task with short circuit checks on likely components, tedious but safe. Once you have (hopefully) found something, check for colateral damage (eg. the driver transistor for T601), and perform voltage checks specified in the service manual (apart from the -1900V one).

Let's see what you find first anyway. If it helps, I would far rather be debugging and fixing that scope than a Tek.

[james_s]

Thanks all. Don’t worry, the dust will be banished.

Gyro, James, just to clarify, as tomorrow will be at least 48 hours cold, am I “totally” safe?
If it’s just the anode, can I discharge that?

Re cleaning, can I clean/remove all connectors at the rear safely?

You're never totally safe, you could drop it on your toe, or prick your finger on something sharp, or trip and fall on it, but I would say the risk of receiving a dangerous shock from it after even just a few hours is negligible. Be careful, respect it, but don't fear it.