开云体育

Hi all,

I acquired a nice & functional set of these recently. The only "flaw" so fare is an error message of the current amp due to an empty battery.

I asked myself whether this battery holds critical data (calibration or such) or if the values retained are merely the results of the degaussing & normalizing action and as such are renewed whenever I press the button. To my surprise I could not find any manual of the 503B that includes circuit diagrams. I checked Artek Manuals, no luck either. I found a more complete service manual somewhere, but without the circuit diagrams!

Reading through what I got about the AM503B, there is mention of the A6302 probe having an offset adjustment for itself. Now I do have 2 other A6302's but they only work in AC. One has a hole for the adjustment screw, the others (including the one I got with the 503B) do no seem to have this adjustment. Again, search for service manuals WITH circuit diagrams was fruitless. All I got were rather detailed dismantling instructions...

Anyone has a link to some source or can provide schematics for these units? Is there something special about the AM503B or the A6302 so Tektronix decided not to provide complete service information?

Thanks & cheers
Martin

Hi Martin,

Unfortunately there is no circuit diagram for the AM503B. But you can use the AM503A. Not all diagrams are the same, but this should be enough to get you started.
Attached is a link to a description of how the AM503B can be calibrated without a GPIB board. The exact process is described in the service manual.

/g/TekScopes/message/183508?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Acreated%2C0%2Cam503b%2C20%2C2%2C0%2C81840398

Best regards
Rico

The battery backed memory in the AM503B is for cal constants in the various ranges, front panel settings for recall when power cycled, and the serial number too.
Ideally the clamp and AM503 are 'tuned' to each other to provide maximum bandwidth, Tek provide information of bandwidth limits with and without the matching in the respective manuals.

There are instructions on how to calibrate them on Tekwiki:



But as mentioned by Rico, the closest schematics available are the AM503A. They come from the era of board level repairs, rather than the component level repair of earlier equipment.
However, the schematics aren't needed to calibrate the unit.

For those clamps that don't read DC, they may have faulty hall effect sensors in the pickup coil, which would mean new pickup coils are needed if that's the case.

One day I'll have to finish the batch file I was making to help make reprogramming the cal constants into the AM503B easier using a BusPirate. Just another project on the long list of stuff to finish....

We have had all three types and all the various probes.

The AM503 503A and 503B are very different and TEK never released a AM503B service to my knowledge.

The backup batter should be easy to find an replace.

Cal may require more details. Rico's note link?

If the probes have no DC response it is a failed or damaged Hall effect in the clamp and you see only the AC signal.

The probes are typically impossible to fix. The adjustmens may also be inside the probe case and not all exposed.

If the probe was off epay and seller said it was good, it probably is not and should be returned.

Bon chance,

Jon

Merci Jean-Paul,

The AM503 503A and 503B are very different and TEK never released a AM503B service to my knowledge.

OK... pity!
I was surprised as I repaired / serviced some advanced TM5000 modules recently, that also have computer control but with complete service documentation available.

The backup batter should be easy to find an replace.

Sure. For the CAL constants, does that mean they are lost and have to be re-fixed after replacement? Acutally, the error message is "NV-Ram failure". But I also saw the "Lo" sign in the readout, so I guess its just the battery that is unable to hold data in the NV-Ram.

Acutally it seems to be a V-Ram... (volatile) ;-)

The probes are typically impossible to fix. The adjustmens may also be inside the probe case and not all exposed.

I was puzzled since there are A6302's with the hole for adjustment and others without. Does that mean the adjustment is inside, but only accessible when dismantling the probe??

cheers
Martin

On Thu, Nov 4, 2021 at 11:27 AM, Martin wrote:

I was puzzled since there are A6302's with the hole for adjustment and others without.
Does that mean the adjustment is inside, but only accessible when dismantling the probe??

The early A6302 has no hole and no trimpot. Instead it has a selected resistor inside (still exactly as in the P6302).
See the manual 070-02897-00 at Tekwiki.

W.r.t. AC only, you might verify at the (disconnected) probe plug that you see resistances of several hundredths of ohms (but below 1 k IIRC) between any two terminals of the Hall sensor (A, D, E, F). In a probe with hole the trimpot is also wired between A and D but has larg(er) resistance.
Albert

To all,

I just uploaded a couple of extra documents that might prove handy for the AM503B.
“AM503B, AM5030, A6300 067-0270-00 Verification & Adjustment Kit 070-9352-01.pdf” instruction manual.
“AM503B - AM50XX Declassification Document rev4-1.doc” a MS Word document dated November 4, 2021. Interesting date since I first came upon it in March of 2019.

To drill down on AM503B documents in the Files section of this site be sure to enter the search term in quotes (i.e. “AM503B”) in the search field.

Enjoy.

Greg

Hi Greg,

thanks for the files. In essence, according to the "declassification document", I could just take out the battery and setup the AM503B each time I use it.
Thats wouild not be a big deal: connecting the probe, selecting A/div and doing the degauss. All things I have to do anyway.

The amp seems a little bit over-engineered at that point.

cheers
Martin

In the old probe without the hole there is a select on test resistor inside to help null the offset on the hall device. It can be set to either a positive offset or negative by moving one of the terminals.
There is also an adjustment on the AM503X that can also be used. If due to age, the 503X can not compensate for the offset, the resistor can be changed.
I usually use a resistor at about half of the original with a pot in series at about 2X the original. With the AM503X offset set to center, adjust the pot connected to the probe to null. If needed move the terminal to the opposite polarity or change the pot or reduce the resistor value as needed. When done measure the resistor and pot (in series) and the value should be close enough for the offset in the AM503X to take over.
This will only help if there is a constant offset. It can not compensate for a probe that has a hall sensor that is drifting over time.

ed

Hi,

However, this document does not mention that removing the batteries will also lose the calibration constants for the AM503B.
These are set to the default value after a "cold start" (without battery).

best regards Rico

On 8. Nov 2021, at 17:07, Rico Sonderegger <rico.sonderegger@...> wrote:
...removing the batteries will also lose the calibration constants for the AM503B.

Rico,

is this documented somewhere? I guess this happens when I have to change the battery!
How can I put these values back, or is there a way to save them?

cheers
Martin

Hi Martin,

Here is the document that we created.

/g/TekScopes/files/AM503B%20Calibration%20without%20GPIB/AM503B_AM5030%20Calibration_V01.pdf

If you have any questions or need additions, we can add to this document.

Best regards
Rico