Leader LS8106 oscilloscope

[ultrasmurf]

Hi guys,

Wondering if anyone have the procedure on how to calibrate this oscilloscope ? Mine is off quite bad on the time/div, around 15-20%. And the voltage is off by about 10%. I'm using it just to view the waveform currently, but prefer it to be a little bit more accurate, maybe somewhere in 5% range.

[tautech]

I had hoped the manual might have schematics and cal procedures in it but no. 

http://www.eserviceinfo.com/downloadsm/65220/Leader_LS%208105-8106A.html

[ultrasmurf]

thanks for the manual.
anyone with any insight on howthe time/div generally calibrated in oscilloscope ? can i just rip it open and start changing any oscillator i can find ?

[dzseki]

Since both axises are off then I'd suspect a HV problem could that be?

[tautech]

can i just rip it open and start changing any oscillator i can find ?

Only is you really want to ruin it, so NO.

As dzseki has hinted the first thing to check is the PSU is within spec.

Often there's enough clues on the PSU PCB or other PCB's to indicate the correct voltages but you are "flying blind" without a service manual.
All the low voltages, say 30 and less should be within +- 0.1 V of spec with the exception of any that aren't regulated, they can be 2-5 V from spec.
All regulated voltages should have low ripple too, this can be checked with a DMM set to AC volts that will show the ripple riding on the DC rail.
That the amplitude and timebase are below spec suggests DC supply rail/s might be dragged low by a failing component, possibly a dried out electrolytic or a shorted tantalum cap.
Careful study of the PCB's might enable you to identify parts of the circuit to focus on but it's difficult without schematics and/or significant experience.
But regardless of having the service manual or not the PSU is the first thing to check and it must be correct as the voltages supplied are the reference/s for the scope inherent accuracy.
 
This doc from the sticky in the Repair board is of compulsory reading when attempting to fix CRO's.
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[tautech]

Spent a bit more time searching for a service manual without success. 

I'm thinking you'll need to contact the manufacturer and ask them for a copy of the Service manual and/or schematics.

Many are quite helpful and there's plenty of members that can guide you through the repair.
By all means link them to this thread.

[ultrasmurf]

Already emailed the manufacturer. Let see what kind of respond I will get.
Thanks for the tek basic troubleshooting manual. Good one.

On a side note, I was offered a used Agilent 54622A for ~USD150. No probe, missing handle, looks like it was attached to some machine as some sort of diagnostic panel. Not much testing can be done on site, it boots up ok. I read that Agilent release the latest firmware opening up all the option for this oscilloscope, and was thinking a good serial com port to transfer waveform is pretty handy and reduce my dependency on stable hand capturing waveform on a dimly lit room with old mobile phone... Read up on the service manual and calibration seems like a breeze... though there is no mention on how to check the internal calibration signal source validity.

Should I jump on this offer or just let it go to a more deserving soul ? I dont think I will ever use it to its potential, Im using oscilloscope just to see signal in the most conventional way and highest bandwidth I ever need will be 25MHz...

[singapol]

Hi guys,

Wondering if anyone have the procedure on how to calibrate this oscilloscope ? Mine is off quite bad on the time/div, around 15-20%. And the voltage is off by about 10%. I'm using it just to view the waveform currently, but prefer it to be a little bit more accurate, maybe somewhere in 5% range.

How do you know it is off? What did you calibrate it with or reference it to? LS8106 was their top model then. Are you basing your readings by the screen readouts?

For timebase setting read pg.22.

General setup pg.30.

Stated accuracy of scope is +/- 2%.

[ultrasmurf]

By comparing DC reading with multimeter reading reference voltage source. And by comparing reading of my freq counter reading a crystal oscillator. And it's by counting squares as well as cursor measurement on the osc screen.

I assume you are referring to the user manual ?
The user manual only cover how to operate the oscilloscope, not the nitty gritty procedure to calibrate the time base or the voltage.

[singapol]

By comparing DC reading with multimeter reading reference voltage source. And by comparing reading of my freq counter reading a crystal oscillator. And it's by counting squares as well as cursor measurement on the osc screen.

I assume you are referring to the user manual ?
The user manual only cover how to operate the oscilloscope, not the nitty gritty procedure to calibrate the time base or the voltage.

Great but apart from frequency counter, a signal/function generator  would be helpful too. A proper scope calibrator from Fluke cost a lot of money even 2nd. hand. So the best thing is what is available online.
For voltage reference it's also best to diy a few voltage references from what is commonly termed reference
diodes. a pulse generator for timebase calibration can be useful. You can build this simple scope calibrator
from Ian Hickman's Oscilloscopes 5th. edition. on pg.46 using cmos digital ic. Cd4069 and a transistor.
From 1 Khz. - 1 Mhz. at 5V.

File is about 15Mb. Book gives a working knowledge that can be used to troubleshoot your scope.
http://diagramas.diagramasde.com/otros/Oscilloscopes_FifthEdition_Ian_Hickman.pdf

Edit: Although what I have suggested are only tools to generate signals. As to the accuracy of the signals
you can verify with your frequency counter (time base ) and multimeter (voltage) if it can measure true rms. Also note that scope maesures p-p (peak to peak) so you have to convert between the two using a formula to calculate. I believe there are online calculators. Note at best your multimeter can only go past a little over 1 Khz. or more 100Khz. if benchtop models at -3db. down.

To calibrate your scope would require a schematic or better a service manual that tells what to adjust and measure. If not available a service manual of a similar model or other brand scope would give you an idea of which circuit to adjust the trimpots. good luck. A scope is not an accurate instrument but if you want such accuracy just for knowledge you have to go into volt- nut or time- nut territory..haha. Cost money too.
 
PS: To give you an idea of how a similar readout scope like hitachi V1065A but without auto measurement
is calibrated have a look at the service manual: File size is 11.5 Mb.

http://elektrotanya.com/hitachi_v-1065a_v-1060_v-665a_v-660_sm.pdf/download.html

[tautech]

Unless you've tweaked a few scopes before don't consider trying without a service manual and some accurate references.
Even those that are familiar with any particular scope wouldn't dream of attempting scope without a manual unless it was extremely basic and this Leader is not.
After checking the PSU was OK and there was no silly faults, resocket all connectors and ICs there's not a lot more other than signal path tracing to find a crook stage.
But be patient and Leader might send you the manual or a member might see this thread and offer a copy.

[ultrasmurf]

Opened it up, while trying to refer to 1021, 516, and 8022 service manual. Nothing seems close enough to it... No obvious power supply issue, no burnt mark anywhere... In fact it looks surprisingly clean and good considering that I obtain this, used, more than 10 years ago and never attempt any cleaning or opening.

And after reading all the service manual it seems that different time base has different vr to adjust. So true enough, my time base >1us is accurate enough for me. Within 2-3% of my "ref" signal all the way to 1MHz. Only when selecting <1us I see the 10-15% error (my previous 20% is a little bit too exaggerated). And error % is quite consistent for all selection below 1us.

[tautech]

Hey a thought, are the front panel variable pots for amplitude and time base in the uncal position?

[ultrasmurf]

Nope.. it's in the cal'd position. It shows up in the "cursor" measurement immediately when they are not in the cal'd position.

[ultrasmurf]

Got the service manual from Leader...  I didn't expect that they will release the service manual to individual. Anyway, waiting for their reply as to whether they allow me to post it here.

[tautech]

Got the service manual from Leader...  I didn't expect that they will release the service manual to individual. Anyway, waiting for their reply as to whether they allow me to post it here.

Hopefully its a PDF and they don't mind if you upload it to one of the free file repositories so others can have access to it too.

[ultrasmurf]

Got a reply from Leader Japan, they ask me not to upload the service manual. Anyway, they seems to be helpful, so by all means try to reach them if you need the service manual.

I sent email request to both US as well as Japan office, both gave me the manual.

Anyhoo, got mine "calibrated" to within 5% on the time base (only on 1 of the setting while other 2 goes within 1%) and within 1% on the voltage division. I guess I have some dried up or reduced value capacitor that I need to hunt down to get the time base to within 1%, since one of the adjustment cap is not able to fully compensate the time base.