Re: TDS540 Calibration Procedure??

Denis Cobley <denis.cobley@...>

I have some bad news then.
Without a Tek Scopecal ATE system or the software + all the required test
equipment specified in the manual you have no chance.
Even with this you will have an uphill battle.
The first step in all these cals is to run the SPC - if this fails it
normally will bug out of the cal process.
The SPC only does DC gains & balances/offsets - it is NOT a calibration -
that is why it's called "Signal path compensation".
If it was a self cal the Tek would have called it that (some scopes do have
that capability like the 11K series).
I have been involved in many repairs on this product with the Tek ATE which
you can force past the SPC pass requirement. In almost every case you then
end up with a power up failure and / or a Cal failure on the cal status
This is because you actually have a fault but it is more a degradation of
performance of the digitiser ASIC for a channel.
The message is "Dac Value out of bounds" which means the unit cannot get the
adjustment to pass and meet the engineering limits Tek set on the DAC number
for a particular adjustment (normally 700-4500 or similar - varies from
model to model) that is stored as the corrected value for that function.
Good luck going forward - you will need it.
As a general warning to all on the list - buying any TDS500 (or most TDS
scopes) if they show acquisition failures then you had better be prepared to
lose all your money because other than leaky caps you have a low chance of
completing a successful repair (passes all daigs and cal with a clear error
log). I would insist on a picture of the error log if I was buying to use it
as a scope (I often buy for parts).
If the error log was clear, it passed SPC and showed all passed on the cal
status then you are reasonably OK (other than it is out of support and Tek
have no parts if you could afford them)
If Tek had an exchange acquisition board it could cost about $2000+ a full
cal after fitting it.
Working TDS scopes are a great scope - faulty ones are not.
Denis Cobley

----- Original Message -----
From: "gettingalongwouldbenice" <>
To: <>
Sent: Friday, August 20, 2004 10:59 AM
Subject: [TekScopes] Re: TDS540 Calibration Procedure??

--- In, "Denis Cobley" <denis.cobley@n...>
SPC has to pass before you attempt any cal adjustments - if SPC
failed then
you still have a 95% chance of a hardware problem.
You seem to have a DAC problem.
snipped very helpful input.

Thanks for the suggestions. I'll go see if I can figure out
what's happening in the DAC system.

Let's look at the SPC logically. Since I don't have any real facts,
that's all I got. My understanding is that SPC can compensate
for minor temperature variations in the calibration. If it would
pass with ANY or CORRUPTED calibration data, there'd be no need to
ever (externally) calibrate the unit. It would just self-cal and meet

I propose that a badly miscalibrated unit might fail SPC???

If the calibration constants are so far out that the minor tweeking
of SPC couldn't fix it, one would need to (external) recal to get
things back into the ballpark.

Remember that I've got two acquisition boards with the same symptom
on all 8 channels. And that the boards have been swapped around and
the calibration constants blown away. The control board probably
isn't even sure whether it's a 520 or 540.

Now, if you'd said that it has to pass power on self test before
attempting calibration, I'd agree. It does pass that test.

Bottom line is that eventually I'll need to calibrate the system.
Where can I find the calibration software? I tried to look in
the tekscoparc group, but the moderator either isn't paying attention
or doesn't want me in there. :-(

I do have a working TDS540, but I'm unwilling to swap boards into there
until I have the calibration issues resolved. I already got two
bad scopes...I don't need three ;-)

Thanks, mike

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