Trio Osilloscope

[Graham]

I have a 20Mhz O-scope, that I use very occasionaly (I'm a hobiest) .
I've had it for about 10 years and it has proved very reliable and
still gives a nice bright crisp display. I was using it the other day
and I noticed a very slight wobble in the trace, so I hooked it up to
the calibration loop on the front. I then saw that it was about 10%
out on the timebase calibration (yes I did check the cal knob). I'm
not really worried about the wobble and I've compared the voltage cal
to that of my 2 DMM's and it seems spot on. But how do I check the
frequency cal. Neither of my 2 meters have frequency on them and I
don't trust the knob on my fuction generator or the cal point on the
scope. So what's the best way? how close could a crystal oscilator get
since I have a few knocking around. I don't want to pay to get
calibrated since that will cost more than the scope is worth.

Many thanks
Graham

PS anyone got a service manual / schematics for a Tek 7603?

 

[Sam Goldwasser]

Line voltage, 50 or 60 Hz depending on where you live.

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[Jim Yanik]

I have a 20Mhz O-scope, that I use very occasionaly (I'm a hobiest) .
I've had it for about 10 years and it has proved very reliable and
still gives a nice bright crisp display. I was using it the other day
and I noticed a very slight wobble in the trace, so I hooked it up to
the calibration loop on the front. I then saw that it was about 10%
out on the timebase calibration (yes I did check the cal knob). I'm
not really worried about the wobble and I've compared the voltage cal
to that of my 2 DMM's and it seems spot on. But how do I check the
frequency cal. Neither of my 2 meters have frequency on them and I
don't trust the knob on my fuction generator or the cal point on the
scope. So what's the best way? how close could a crystal oscilator get
since I have a few knocking around. I don't want to pay to get
calibrated since that will cost more than the scope is worth.

Many thanks
Graham

PS anyone got a service manual / schematics for a Tek 7603?

Analog scopes typically have a 3% 'accuracy' for timebases.Xtal oscillators
are far more accurate,even the cheap TTL clocks for PCBs are 0.1%;all you
need is 4x better.Nut's and Volts magazine had an article a few years ago
on how to buid an inexpensive scope timebase calibrator using a TTL
oscillator and some CMOS dividers.Electronic Goldmine USED to offer a kit
for it.

TEK 7603 is a good scope,pay attention to the solder joints on the PS
regulator PCB power transistor studs.They crack from temp cycling and cause
problems. The chrome plating on the brass studs prevents good wetting of
the pin.I used to sand off the pin's plating,and resolder them.

 

[Graham]

Analog scopes typically have a 3% 'accuracy' for timebases.Xtal oscillators
are far more accurate,even the cheap TTL clocks for PCBs are 0.1%;all you
need is 4x better.Nut's and Volts magazine had an article a few years ago
on how to buid an inexpensive scope timebase calibrator using a TTL
oscillator and some CMOS dividers.Electronic Goldmine USED to offer a kit
for it.

TEK 7603 is a good scope,pay attention to the solder joints on the PS
regulator PCB power transistor studs.They crack from temp cycling and cause
problems. The chrome plating on the brass studs prevents good wetting of
the pin.I used to sand off the pin's plating,and resolder them.

Great, I shall see if I can dig it up. My real problem is I have no
reference, so how do I know that a 1mhz is 1mhz. I have a couple of
TTL blocks laying around...... I'm not after pin point accuracy, but
if I can get 3% that would be nice.

My TEK is a recent purchase, it all lights up but has no beams. I
haven't gotten round to looking inside yet so it might be something
simple (probably not!). I shall have a look the studs though, sounds
like it would worth doing even if that isn't the fault. any other
tips?

Many thanks
Graham

 

[Graham]

On 26 Jan 2004 15:17:05 -0500, Sam Goldwasser <[email protected]>
wrote:

That's an idea, but I didn't think that line frequency was that
acurate. I'm in the UK, I'm sure I remember something like +-3% for
mains frequency? I think I'll go down the TTL crystal route mentioned
in the other post since I have a few of those on hand.

Many thanks

 

[Sam Goldwasser]

On 26 Jan 2004 15:17:05 -0500, Sam Goldwasser <[email protected]>
wrote:

That's an idea, but I didn't think that line frequency was that
acurate. I'm in the UK, I'm sure I remember something like +-3% for
mains frequency? I think I'll go down the TTL crystal route mentioned
in the other post since I have a few of those on hand.

Over here, long term accuracy is close to an atomic clock.

Short term I don't know but I'll bet it's much better than 1 percent.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.