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oscilloscope question

D

Dave

Jan 1, 1970
0
I'd like to know what the minimum useful bandwidth is for an oscilloscope to
be used for general TV and audio equipment troubleshooting and repair. I've
stumbled across a 20MHz dual-trace scope at a second-hand store, it appears
to work and they only want $50 for it. The brand is "Leader" which I'm not
familiar with. Comments?
 
T

Tim

Jan 1, 1970
0
I'd like to know what the minimum useful bandwidth is for an oscilloscope to
be used for general TV and audio equipment troubleshooting and repair. I've
stumbled across a 20MHz dual-trace scope at a second-hand store, it appears
to work and they only want $50 for it. The brand is "Leader" which I'm not
familiar with. Comments?
Hmmm, I recall that Leader had a fairly good name in the past. And the
company I worked for bought me a 20Mhz dual trace model to do service
work on video equipment. Of course this particular unit maybe modified
or damaged in some way, but I would likely buy it if I knew it hadn't
been abused.

- Tim -
 
I

ian field

Jan 1, 1970
0
Dave said:
I'd like to know what the minimum useful bandwidth is for an oscilloscope
to be used for general TV and audio equipment troubleshooting and repair.
I've stumbled across a 20MHz dual-trace scope at a second-hand store, it
appears to work and they only want $50 for it. The brand is "Leader"
which I'm not familiar with. Comments?

About 10 to 20Mhz is adequate for most CRT TV diagnosis, in my experience -
the more experience I gained at servicing, the less I needed a scope to
diagnose most day to day faults. IMO it might be better to get by as cheap
as possible until you assess the requirements for servicing flat panel TVs,
there might be other instruments that prove more useful than a CRO.
 
N

N Cook

Jan 1, 1970
0
Dave said:
I'd like to know what the minimum useful bandwidth is for an oscilloscope to
be used for general TV and audio equipment troubleshooting and repair. I've
stumbled across a 20MHz dual-trace scope at a second-hand store, it appears
to work and they only want $50 for it. The brand is "Leader" which I'm not
familiar with. Comments?

An isolation transformer may well cost the same again.
For TV work and isolation transformer is first priority and then a 'scope.
Somewhere in the list comes an ELCB/RCCD/GFCI
Then a variac for diagnosing crowbar problems etc
 
D

Dave

Jan 1, 1970
0
N Cook said:
An isolation transformer may well cost the same again.
For TV work and isolation transformer is first priority and then a 'scope.
Somewhere in the list comes an ELCB/RCCD/GFCI
Then a variac for diagnosing crowbar problems etc

I've already got an isolation transformer and GFCI. What are ELCB and RCCD?

Dave
 
D

Dave

Jan 1, 1970
0
Dave said:
I've already got an isolation transformer and GFCI. What are ELCB and
RCCD?
Sorry, two seconds on my part answered my own question. Hate it when people
post lazy questions to newsgroups.
 
I'd like to know what the minimum useful bandwidth is for an oscilloscope to
be used for general TV and audio equipment troubleshooting and repair. I've
stumbled across a 20MHz dual-trace scope at a second-hand store, it appears
to work and they only want $50 for it. The brand is "Leader" which I'm not
familiar with. Comments?

20MHz is more than enough.


NT
 
C

Charles

Jan 1, 1970
0
Dave said:
I'd like to know what the minimum useful bandwidth is for an oscilloscope
to be used for general TV and audio equipment troubleshooting and repair.
I've stumbled across a 20MHz dual-trace scope at a second-hand store, it
appears to work and they only want $50 for it. The brand is "Leader"
which I'm not familiar with. Comments?

Offer them $35. Leader scopes are decent and the BW is fine for your use.
 
H

Heinz Schmitz

Jan 1, 1970
0
Charles said:
Offer them $35. Leader scopes are decent and the BW is fine for your use.

And have them add the schematics so you can repair it yourself.
Check wether Leader used any proprietary semiconductors and
wether the CRT has burnt in trace.
You may well want to check eBay for comparable offers, too.

Regards
H.
 
J

James Sweet

Jan 1, 1970
0
Heinz Schmitz said:
And have them add the schematics so you can repair it yourself.
Check wether Leader used any proprietary semiconductors and
wether the CRT has burnt in trace.
You may well want to check eBay for comparable offers, too.


More important than burn is to make sure the CRT can still produce a sharp
trace. It should only take a few minutes to plug it in and verify basic
functionality though. For 50 bucks it's hard to go wrong on a working 20 MHz
scope, that's more than enough scope for the average hobbyist.
 
F

Franc Zabkar

Jan 1, 1970
0
I'd like to know what the minimum useful bandwidth is for an oscilloscope to
be used for general TV and audio equipment troubleshooting and repair. I've
stumbled across a 20MHz dual-trace scope at a second-hand store, it appears
to work and they only want $50 for it. The brand is "Leader" which I'm not
familiar with. Comments?

I have a Leader LBO-514 10MHz scope. It seems to be adequate for most
jobs. I had to fix about 50 dry joints, though. If yours is anything
like mine, you will need to redo all the interconnects between the top
and bottom layers of each PCB.

- Franc Zabkar
 
L

Lionel

Jan 1, 1970
0
I've already got an isolation transformer and GFCI. What are ELCB and RCCD?

Other names for GFCI. They're called all sorts of different names
around the world.
 
D

Dave

Jan 1, 1970
0
Franc Zabkar said:
I have a Leader LBO-514 10MHz scope. It seems to be adequate for most
jobs. I had to fix about 50 dry joints, though. If yours is anything
like mine, you will need to redo all the interconnects between the top
and bottom layers of each PCB.

Yeah, another one of those unfortunate examples of the old axiom "there
ain't no such thing as a free lunch".
 
D

Dave

Jan 1, 1970
0
Dave said:
I'd like to know what the minimum useful bandwidth is for an oscilloscope
to be used for general TV and audio equipment troubleshooting and repair.
I've stumbled across a 20MHz dual-trace scope at a second-hand store, it
appears to work and they only want $50 for it. The brand is "Leader"
which I'm not familiar with. Comments?
When the scope is powered up, it has a white line which starts to cross the
screen from left to right. The line gets about halfway across, then
disappears and doesn't come back.

Does this mean the scope is disfunctional? I thought it should have a
steady horizontal line when it's turned on with no inputs.
 
B

bz

Jan 1, 1970
0
When the scope is powered up, it has a white line which starts to cross
the screen from left to right. The line gets about halfway across, then
disappears and doesn't come back.

Does this mean the scope is disfunctional? I thought it should have a
steady horizontal line when it's turned on with no inputs.

That depends on how the triggering is set.

You could be set for single sweep. It almost sounds like that and a slow
sweep at that.

You could be set for triggered sweep and not have a trigger.

You need to play with a properly working scope for a while to learn how to
use it and then you can test a questionable scope.






--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap
 
I

ian field

Jan 1, 1970
0
Dave said:
When the scope is powered up, it has a white line which starts to cross
the screen from left to right. The line gets about halfway across, then
disappears and doesn't come back.

The trace sweeps from left to right and should be blanked on the return
stroke.
Does this mean the scope is disfunctional? I thought it should have a
steady horizontal line when it's turned on with no inputs.

If the trace only goes half way across the screen try centering it with the
horizontal shift control.
 
H

Homer J Simpson

Jan 1, 1970
0
When the scope is powered up, it has a white line which starts to cross
the screen from left to right. The line gets about halfway across, then
disappears and doesn't come back.

The centering is set to the left.

Set all knobs to mid position and try again. Set Sync to Auto.
 
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